The corrosion properties of Spacelab structural alloy - ESMAT

Transcription

ESA STR-212
May 1984
The corrosion properties of
Spacelab structural alloy
aluminium 2219 - T851
B D Dunn
European Space Research and Technology Centre
Noordwijk, The Netherlands
european space agency / agence spatiale europeenne
8-10, rue Mario-Nikis, 75738 PARIS CEDEX 15, France
ii
ESA STR-212 (May 1984)
Copyri ght CD 1984 European Space Agency
Approved for publication:
28th February 1984
Edited by: W.R. Burke
Published by: ESA Scientific
and Technical
Publications
Branch, ESTEC, Noordwijk (NL)
Printed in The Netherlands
ISSN 0379 - 4067
Pri ce code: C2
CORROSION PROPERTIES OF AL 2219
-
iii
T851
ABSTRACT
The
main
structural
aluminium
alloy
Pressure
The
2219.
Shell
atmospheric
material
and the
corrosion
corrosion
selected
for
slip
planes
surrounded
galvanic
must
high
depleated
With
service
demonstrate
be finished
finishes
the
that
with
are
various
all
space
expected
to
have
been
the
CuAlz
oxidised
survive
subjected
salt
of CuAlz
(e.g.
rise
to
which
to
avoid
Spacelab
are
localised
will
the
Alodined)
in order
along
particles
refurbished,
the
to
solution.
weldments,
possibly
to
alloy
involving
and can give
paints
wrought
intermetallic
of
Modular
resistance
programmes
precipitation
and
approved
of
from
the
oxidised.
forms
chloride
exception
chemically
a poor
% sodium
in copper
life
has
is
the
or chemically
test
Large
project
throughout
applications
strength
by a region
during
and
in 3.5
boundaries.
Spacelab
As 2219
anodised
2219
and grain
corrosion.
Anodised
always
the
extensively
stress-corrosion
immersion
its
for
structure.
systems
and
re-inspected
results
is
Spacelab
derives
used
Igloo
it
the
or alternate
2219-T851
is
protection
surface-corrosion
spray
It
chosen
be
test
surfaces
corrosion.
10-year
life
requirement.
2219-T851
in the
(TIG, electron
form of forged rings,
rolled plate
beam and repaired)
has successfully
and welded plate
passed
standard
stress-corrosion
tests.
Samples were stressed
in the short transverse
direction,
at 75 per cent of the 0.2 per cent proof stress,
for a period
of at least
30 days. For comparative
purposes
(equivalent
to AA 2024) was simultaneously tested
the ESA stress-corrosion
requirements.
the
alloy BS L 93
and observed to fail
ESA STR-212
iv
(BLANK PAGE)
(May 1984)
CORROSION PROPERTIES OF Al 2219
- T851
v
CONTENTS
1
GENERAL
INTRODUCTION
2
SURFACE
PROTECTION
3
STRESS-CORROSION
LITERATURE
4
EVALUATION
1
3
TREATMENTS
CRACKING DATA FOR 2219 AS REPORTED IN THE
13
OF THE CORROSION RESISTANCE OF ANODIC AND CHEMICAL
CONVERSION COATINGS ON NONSTRESSED ALUMINIUM
5
4.1
Introduction
4.2
Description
4.3
Experimental
4.4
Results
4.5
Conclusions
EVALUATION
2219 SAMPLES
13
of test
samples
procedure
14
15
and discussion
17
23
OF THE CORROSION RESISTANCE OF PAINTED AND CHEMICAL
CONVERSION COATED SAMPLES OF NONSTRESSED Al 2219 WELDMENTS
6
13
5.1
Introduction
26
5.2
Description
of
5.3
Preparation
of samples
5.4
Test
5.5
Results
5.6
Conclusions
test
programme
samples
6.2
Test
6.3
Results
6.4
Conclusion
30
34
INTERGRANULAR CORROSION TESTING
Introduction
27
28
and discussion
6.1
27
37
procedure
37
37
38
OF WELDED PLATE
37
26
vi
7
8
9
ESA STR-212
(May 1984)
METALLURGICAL EXAMINATION OF 2219 - T851 IC. RING SAMPLES (THICK
PLATE) AFTER STRESS-CORROSION TESTING
38
7.1
7.2
Introduction
38
Material
details
38
7.3
Method of examinati
on
7.4
Resul ts
7.5
Conclusions
METALLURGICAL
39
40
40
EXAMINATION
OF 2419
- T851
ROUND TENSION BAR SAMPLES
(LARGE FORGED RINGS)
AFTER STRESS-CORROSION
8.1
Introduction
43
8.2
Material
8.3
Experimental
8.4
Resul ts
8.5
Conclusion
data
43
procedure
44
45
50
STRESS CORROSION OF 2219 - T851 WELDMENTS
9.1
Introduction
51
9.2
Test procedure
52
9.3
Results
55
9.4
Discussion
71
9.5
Conclusions
76
ACKNOWLEDGEMENT
APPENDICES
77
TESTING
74
51
43
1
aluminium-copper-magnesium
The
the
GENERAL
AA 2000
series
used
extensively
alloys
2618
spacecraft
high
were
for
and
alloy
is
aerospace
structures.
have
Its
wrought
and
been
when good creep
chosen
in the
In
for
strength
alloys
belonging
to
1920's
and have
been
decade
the
the
last
advanced
was required
aircraft
and
together
with
properties.
a heat-treatable
1954. It provided
industry
( 2600 C-30oo C) propert i es
alloys.
wrought
developed
strength/elongation
The 2219
(silicon)
initially
2219
projects
INTRODUCTION
weldability
we 1ded
wrought
with a material
exceed i ng those
is excellent.
2219
are
also
alloy
developed
by Alcoa
in
having
elevated-temperature
of
a 11 other
a 1urnin i urn
The mechanical
exce 11 ent
at
properties
temperatures
of both
down
to
-2500 C.
As with all AA 2000 series alloys, 2219 has somewhat less resistance
to
atmospheric
corrosion than the lower strength Al-Si-Mg (AA6000 series)
and Al-Mg (AA 5000 series)
wrought alloys.
Inhomogeneities
frequently
initiate
localised surface corrosion attack and for maximum resistance
to corrosion
the composition of each aluminium alloy must be kept as
homogeneous possible.
This principle
applies to all the AA 2000 series
of alloys, of which 2219 is typical.
percent by weight) of 2219 generally
of aluminium
Table 1.
in
the
cathodic
The high copper content
depresses the electrode
(more
noble)
direction,
as
(5.8 - 6.8
potential
shown in
From both a mechanical-strength
and an optimum corrosion-resistance
standpoint
it is essential
that,
during alloy fabrication,
copper
should be fully dissolved into the aluminium. It is the solid-solution,
or homogenising,
treatment
that dissolves
the copper, and this
is
performed
in the temperature
range 53P C:tP C. Cooling from th i s
temperature must be rapid to prevent the formation of the intermetallic
2
compound CuA12 at the grain boundaries.
intermetallics
do form
at
adjoining
volumes of alloy
corrosion
attack.
grain
If excessive
boundaries
depleted
they
in copper,
numbers of CuAh
are
and this
surrounded
will
by
facilitate
The selection
of a main structural
alloy for the European Space Agency
(ESA) Spacelab project was made in the mid-70's.
A decision to select
the alloy
2219 was based on the need for
a material
having
an optimum
combination
of properties
including
those of mechanical
strength,
fracture
toughness
and res i stance to general corros ion and stresscorros ion crack ing. Thi s materi a 1 was commerci ally
and plate, extruded rod and bar, it could be forged
avail ab le as sheet
and made available
as Alclad
information
sheet
and plate.
TABLE I
Group
No.
-
A wealth of 2219 property
COMPATIBLE COUPLES FOR BIMETALLIC
Metallurgical category
EMF will tend to corrode
end form
. calomel
--
Gold, solid or plated; gold-platinum allovs; wrought platinu81
+0-15
2.
Rhodium plated on silver-plated copper
+0'05
3.
Silver, solid or plated on copper; high silver alloys
4
Nickel. solid or plated; monel metal and high-nickel:copper alloys; titanium
- 0.15
5.
Copper. solid or plated; low brassesor bronzes;silver solder; German silver;
high copper-nickel alloys; nickel-chromium alloys; austenitic high
corrosion-resistant steels
- 0.20
6.
Commercial yellow brasses and bronzes
-0.25
7.
High brasses and bronzes; naval brass; Muntz metal
- 0.;30
1.
O.
8.
18% chromium type corrosion-resistant s' :cls
-0.35
9
Chromium or tin plated (non-porous) metals, 12% chromium type
corrosion-resistant steels
-0045
10.
Tin-lead solder, solid or plated; Terne plate
-0.50
11.
lead, solid or plated; high lead alloys
- 0.55
22 i'1_:
12.
Duralumin type aluminium wrought allOYS'
13.
Iron, wrought, grey or metalleable; Armco iron; plain carbon and
low alloy steels
- 0.70
14.
Aluminium, wrought alloys other than Duralumin type; aluminium
case alloys of the silicon type
-0.75
15
~Iuminium,cast alloys other than silicon type; cadmium platings
(generally not approved for space-use)
- 0.60
-
~-0.80
16.
Hot dipped zinc plate (generally not approved for space-use)
- 1.05
17.
Zinc, wrought: zinc-base die casting alloys; zinc plate
(generally not approved for space-use)
-HO
18.
Magnesium and magnesium-base .lIoys, cast or wrought
- 1.60
NOTE:
Many of the less
Maximumpotentia' dlff....nce for
electrode
and...
oxi..
noble metals
CONTACTS
Compatible coupl..
EMF betw_n
Th. metal. havingthe g,..ter "8OMI".
was in
AI
Non~cI..nroom
0.25V
any.ronment
I
0,5 V
BI
CI_n-room or hermetlcall,
' ...Iad environment
!
!
I
I
I
I
I
I
j I
!
I
shown in this
I
I !
I
I
tabulation
require
additional protection from general surface corrosion in the
form of platings, conversion coatings, anodic films, paints,
etc.
CORROSION PROPERTIES OF Al
existance
and although
-
3
T851
the majority
was also made available
to utilise
this alloy.
Several
2219
emanated from the United States
by European users
types of corrosion
characteristics
who had only recently
had been established
it
begun
for the
2219 alloy. General surface attack and pitting
corrosion were not
considered difficult
to control,
so by far the greatest
importance was
attributed
fact that
to
this
the control
of stress-corrosion
cracking.
Despite
alloy has been designated as having a high resistance
the
to
stress-corrosion
cracking when in the T6 or T8 condition,
it can, if
incorrectly
worked or heat treated,
have an increased susceptibility
to
all types of corrosion
(see NASA MSFC Spec 522A and ESA PSS-01-736).
A general
prequalification
suitabil ity of 2219 alloy
programme was undertaken
cast, wrought and fabricated
to assess the
in Europe for
the Spacelab Project.
This paper summarises a part of that programme
which evaluated the surface and stress-corrosion
resistance
of samples
of 2219 processed into Spacelab hardware configuration.
Some of the
Space 1ab we1dments are high 1i ghted in Figures 1 to 7. NASA has a1so
utilised
aluminium alloy 2219 extensively
(Figures
8 to 10).
2
SURFACE
PROTECTION
in the Space Shuttle
vehicle
TREATMENTS
The corrosion
protection
of 2219 can be greatly
variety of surface treatments.
improved by a wide
Those chosen for use by ESA projects
are summarised in Table II. The
Alclad forms of 2219 have a very high inherent resistance
to corrosion
and may be used without
the application
of further
protective
coatings.
The most effective
protection
against
stress-corrosion
cracking of machined structural
parts is obtained by the application
of
an epoxy-polyamide
the alloy.
paint
to
shot-peened
or electroplated
surfaces
of
4
ESA STR-212
TABLE II
ALCLAD
-
PRODUCTS
(May 1984)
SURFACE TREATMENTS FOR THE ALLOY 2219
A core
of 2219 sheet material
is
sandwiched
between thin
sheets
of
either
pure aluminium or 7072 alloy,
then hot rolled to effect bonding.
Surface
has a high resistance
to
corrosion
and is sufficiently
anodic
to the 2219 core to afford
electro-chemical
protection.
MECHANICAL FINISHES
Sand blast i ng or shot peen i ng gi ves a
rough matt finish which causes
surface of 2219 to be under s 1i ght
compression.
This may slightly
reduce
suscept i bil ity to general and stress
corrosion but must be covered with an
organic coating.
ANODISING
Anodic coatings formed by electrolysis
in sulphuric
acid or chromic acid
baths. Sulphuric acid provides
thickest
and most corrosion protective
finish (2 to 25 ~m depending on
anodising time) for 2219.
CHEMICAL CONVERSION
COATINGS
Processes
provide
protection
excellent
ELECTROPLATING
2219 can be immersed in sodium zincate
of controlled
composition.
This
is
a satisfactory
base for
depositing
finishes
of copper
then nickel,
chromium, gold, silver,
etc.
PAINTING
Oil and oxides on 2219 must be removed
by dipping
2219
in solvents
then
such as Alodine and Irridite
only
temporary
corrosion
on 2219. They are an
base for paints.
phosphoric
acid (room temperature).
Surface can be mechanically
treated,
primed with a conversion
coating or
special
primer,
then painted
with
epoxy
polyamide
or polyurethane
resins.
2219
-
T851
5
I
-l~
I I (",j
,~
-;~:J~:-~-~
--
N' !
c-q
I
,-in
;
~
r
S
a
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M
I
iil
t--
o
~
~
/
'1
'
~
I
co
N..
':T
m
I
co
I'
I'm
~
M
N
N
I'co
N
':T
I'
':T
M
,
N'"
61
7-
J~'-=cor
LD
LD
M
':T
mo
co':T
..-
N
N
M
co
I'
r- (l) o~£ L--i
1
>I
co.
I'
co
M
N
~1
0
--
>-
:E
:E
~o
zo~
w
u;~
Zo...
W(J)
~(J)
o~
...J...J
...JZ
4:::>
Figure
1
-
Spacelab
Short
Module,
physical
dimensions.
TIG welding
processes were used to weld panels and rings for Modular Pressure Shell.
Base material is 2219 T851 (plates and rings), filler metal is 2319 (to
QQ-R-566) .
Thicknesses of weld configurations
are:
weld 4 mm
Cone
Cylinder - Longitudinal
Circumferential
weld 4 mm
-
Longitudinal
weld 7 mm
Circumferential
weld 7 mm
6
ESA STR-212
(May 1984)
"
./
.,,/'
--'
/"
/
/.;
,/"
/
/"
r',,('/
\
\
\
\
I
\
\
'
\
\
DESCRIPTION
\//
,
\
\
\
\,
\
1
PRIMARY
STRUCTURE
2
SECOND.
STRUCTURE
3
COVER
4
MOUNTING
5
FEEDTHROUGH
6
SEAL ASSEI1BL Y
STRUCTURE
PLATES
\,
\
\
\
Figure 2 - Igloo Structure Lay-Out and Equipment List, fabricated
2219-T851. Both primary structure
and cover welded by Electron
Process.
from
Beam
-
7
T851
..,.. iii' -
"'"
Figure
3 - Aft end cone showing
the fire
extinguisher,
hand rails
foot support.
Circumferential
and longitudinal
TIG welds are arrowed.
panels
are chromic
acid anodised;
ground,
polished
and brush Alodined.
and
All
8
Figure
waffle
ESA STR-212
4 - Cone
pattern
shell panel showing the numerically
controlled
seam TIG welds.
and location of longitudinal
(May 1984)
machined
-
9
T851
,
\
i
Figure 5 - Detail of waffle structure
and interpanel
weld zone. Surfaces
were chromic acid anodised
and the area to be welded was masked
approximately 20 mmwith special tape. This post-welded surface was later
brush Alodined.
10
ESA STR-212
(May 1984)
,#
Figure 6
check-out
-
General
building
view of Spacelab
at KSC.
processing
area
in the operation
and
'.
Figure 7 - Early on-board activities
during the Spacelab 1 - mission.
Crew members Robert Parker and Ulf Merbold carrying out a
"ballistocardiography"
investigation
(November 1983). The brush Alodined
weld zones on the aft end cone are arrowed. Post-flight
inspections
of
these accessible
surfaces showed no evidence of degradation by corrosion.
- T851
11
ORBITER
Figure
8
-
2219
is
a major struct ural
material
O
t
for the NASA Orblor.
ESA STR-212
12
~
~
.
(May 1984)
.::::::{~
"~':;-~'
Figure 9 - Crew module weld locations on Orbitor. Material is 2219 in the
following
tempers:
parts requiring
little
or no metal forming - T87;
severe doub 1e contour - T62; and sing 1e contour - T851. Tempers are
described in Appendix II.
INTERTANK
LH2TANK
lO2 TANK
Figure
Boosters
10
-
The external
(recoverable
aluminium alloy
in the
after
Tank shown above,
- T87
parachuting
condition.
into
and the
two Sol id Rocket
2219
the ocean) utilise
-
STRESS-CORROSION-CRACKING
3
IN
Several
2219
of
have
Appendix
the
reproduced
1. For
a further
original
EVALUATION
DATA
2219
FOR
graphs
from
the
explanation
and Tables
literature.
of
this
related
They
data,
Panel
REPORTED
to
are
the
alloy
presented
reference
must
in
be
papers.
OF THE CORROSION RESISTANCE
OF ANODIC AND CHEMICAL
CONVERSION COATINGS ON NON-STRESSED ALUMINIUM
4.1
AS
THE LITERATURE.
important
been
made to the
4
most
13
T851
2219 SAMPLES
Introduction
samples and a weld sample of Al 2219 were received
from
Air
Italia
(AIT) for corrosion testing.
The panel samples had been chromic
acid anodised and the weld sample Alodined. These surface finishes
were
proposed as a means of protecting
the structure
of Spacelab against
general
corrosion
from the sheltered
environment
afforded
by the
mechanical ground support equipment (MGSE).
The current Natural and Induced Environment Specification
states that
Spacelab shall be capable of tolerating
the following conditions
during
non-operational
storage
Temperature:
Humidity
Pressure
phases on the ground:4" C to 5SOC;
10% to 90% RH;
Ambient.
Except under emergency conditions,
exposed to uncontrolled
terrestrial
This chapter
investigate
protection
concerns
an experimental
Spacelab equipment
environments.
not
be
programme which was undertaken
to
the corrosion
susceptibility
finishes
for the high strength
will
of the proposed
surface
structural
alloy Al 2219.
ESA STR-212
14
4.2
4.2.1
Description
(May 1984)
of Test Samples
Anodised Samples
Four anodised samples were submitted.
Each had been cut from the same
large test panel of 2219 in the T851 condition.
Pretreatments
and
chromic acid anodic oxidation
were according
to the contractors'
specifications.
The test panel was a preproduction
of the core shell
having the waffle pattern shown in Figures 4 and 5.
As one d imens i on of th i s pane 1 exceeded the depth of the anod i sing
tank, it was impossible to oxidise completely in one step. The vertical
panel was therefore
partly submerged into the chromic acid electrolyte
and anod i sed, then 1i fted out and rot ated in order to anod i se the
untreated surfaces.
The mid-plane of the panel was consequently exposed
to two anodisation
treatments,
the last of which produced a dark
immersion-line
stain
been identified
according
First
over the panel
width.
to the following
anodisation
The submitted
had
sketch:
Anodised once
(lst) .
no. 0 (not used)
n""
I
samples
I
L-J
Immersion line
stain from
2nd anodisation
Anodised twice
Second anodisation
L-J
no. 1
J
n
L-J
Anodised once
(2nd)
I
4.2.2
Welded and Alodined
As-received
7 mm plates
- T851
15
(Treatment
were cleaned
1200) Sample
with Freon TF. 20 mmwide surface
bands adjacent to the plate edges to be welded were prepared by buffing
and re-cleaning
in Freon TF. The plates were then TIG welded, using a
filler
rod of Al 2319. These welds were later shaved, etched,
dye
penetrant-tested
recleaned
and chemical
conversion-finished
with
Alodine 1200. They are
Figures 1 and 3.
4.3
Experimental
4.3.1
representative
of
the
cone
welds
shown in
Procedure
Visual Inspection
All surfaces
were examined under a binocular
microscope.
Certain
aspects of the anodised and Alodined finishes
were viewed in detail
with a Reichert
4.3.2
projection
microscope.
Thermal Cycling of Anodised Finish
One small (16 cm2) specimen was carefully
sawn from an area of the
panel which had received a double anodisation.
to the copper heater plate of a thermal cycling
low outgassing
thermal cycles
This piece was attached
equipment by means of a
high thermal conductivity
silicone
paste. Following 100
between -15<PC and +10CPC, under a vacuum of 10-6 torr,
the sample was re-examined
at x600 magnification
for
signs
of surface
crazi ng.
4.3.3
Surface
Surface
Roughness of Anodised Samples
roughness
measurements
4.3.4
Corrosion Resistance
a) All
submitted
samples
were made with Talysurf
were scribed
with
equipment.
a "standard"
scratch
by
16
means of a constant load applied via a diamond pyramid indentor.
depth of the scratch was such that it would just break through
anodised
finish
b) All panels
and reveal
and plates
to provide
five
the underlying
were carefully
rectangular
attached
to each surface
edges of the test pieces
test
to the scratch
Self-adhesive
for traceabi 1ity
were completely
numbers were
purposes.
The bare cut
masked with impervious
shellac.
Once the masking varnish had dried, the test
distilled
water and dried with a soft cloth.
each
the
2219 alloy.
cut transversely
pieces.
The
pieces were washed in
Four test pieces from
sample
were then subjected
to a 5% salt
spray test
accordance with ASTM B 117 except that the exposed surface
inclined approximately 6 degrees from the vertical.
in
was
The remaining "as-received"
test pieces were kept in a desiccator
(containing
silica
gel) for control
purposes.
Test pieces were
withdrawn from the salt spray chamber at intervals
of 7, 14, 21 and
30 days. After exposure, they were thoroughly cleaned with distilled
water, dried and stored in a desiccator.
c) At the
end
photographed.
of
the
30-day
exposure
Every
surface
was
against
standards
accept/reject
criteria
test,
all
closely
test
examined
pieces
and
were
compared
(visual
aids)
which
identified
certain
(i.e.
the specimen panels shall show no more
than a total of 5 isolated spots or pits, none larger than 1/32 inch
in diameter,
in a total of 30 square inches from one or more test
pieces).
The surfaces adjacent to the "standard scratch" lines were
examined separately.
d) The peel or pull-off
was assessed
e) Sections
strength
by a method utilising
were carefully
marked for further
bakelite,
of coatings
ground
adhesive
sawn from several
metallographic
and polished
after
the 30-day exposure
tapes.
test
pieces
examination.
to
1/4 Jlm finish
which had been
They were mounted in
and viewed with
Reichert
projection
microscope.
Photographs
of the as-polished
microsections
were taken at various magnifications
up to xl000.
Occasionally,
polarised
light
was used to highlight
certain
intermetallic
phases.
a
-
4.4
and Discussion
Results
4.4.1
Surface
The
17
T851
as-rece
Inspection
i ved
surface
finishes.
network
of
surface
crazing
test
of Protective
pane 1s were
The
crevices
anodic
and
or
Films
noted
film
pit
to
is
seen
marks.
It
micro-cracking
have
rough,
to
is
be
loured
in
a fine
covered
noted
became
grey-co
that
visible
no
additional
after
temperature
cycling.
4.4.2
Pits
The
on Surface
rough
surface
highlighted
in
non-exposed
test
betweeen
by the
the
appearance
Figure
alloy
11.
and
that
by the
following
The
material
is
particles
having
which
potentials
of
the
enhances
of
microscopic
for
been
between
local
and
instance
their
were
are
is
anodised
far
to
in excess
that
anodic
have
many pits
treatment
wi 11 account
the
of
measured
extend
paths
that
is
depths
of those
tunnel-like
explained
sample
a microsectioned
from
measured
noted
narrow,
into
such
as that
submitted
sheet
by a chemical
etching
for
surface
5 - 8 ~m which
the
deep
of
intermetallic
strung
particles
have
by
experiments
to
matrix).
The
etch-cleaning
an uncontrollable
electro-chemical
surrounding
12.
surfaces.
parallel
to
a composition
of
to
Intermetallic
aluminium
undoubtedly
by the
between
corrosion
pure
procedure
manner
cells
out
exhibit
and -0.53V when coupled
-0.84V
in Figure
are
These
shown
in
a distribution
contain
direction.
etch-pitting
details
Sample
reasoning.
lengths
alloy
shows
pretreatment
to
has
as-received
values
to the
noted
sheet-rolling
the
The contractor
th is
Anodised
pits
as it
prior
pits
seen
Several
by following
in Figure
process
particles
of
which
technique,
had been deoxidised
(i.e.
11
piece.
Talysurf
arrowed
CuA12
IIAs-receivedll
30 and 40 ~m. These
aluminium
the
of
formation
exposed
particles
of
CuA12
are
18
ESA STR-212
"'~-
Figure11
(May 1984)
-
- Topography of anodised
depths may reach 40 microns.
surface
of as received
material.
Pit
12 - Microsection
made through region shown in figure 11.
Photographed
with polarised
light to reveal opaque anodic film and copperrich inclusions.
(xlOOO)
Figure
-
4.4.3
The
Thickness
of.Protective
appearance
of
distinguish
by
light.
The
was
under
polarised
consistent
to
around
light
the
The
thickness
(Figure
of
of
of
assessed
from
Talysurf
-
I
I
I
Panel
film
12.
Anodised
twice
Visual
overall
of
Inspection
the
visual
appearance,
inspections
view
of
a) The anodised
corrosion.
could
not
Actual
values
in
results
Depth
The
even
these
pieces
anodic
after
test
are
A120g
to have
a
protective
be
noted
films
completion
determined
for
the
are
shown
Average
100
50
7
Exposure
to Salt
following
Spray.
exposure
tests
pieces
possess
of
III.
Line
7.5
5.0
2.5
maintain
were
ON 2219
(~m)
to
surface
in Table
Centre
of
by
4.2.1)
Paragraph
(~m)
Following
corrosion-resistance
noted
as a continuous
sketch
Max.
spray
incident
microsection
is
Open Pit
once
salt
thin.
(see
13. Alodined
I
the
tilted
layer
present
Average
no.
Anodised
Results
slightly
white
to
semi-opaque
SURFACE ROUGHNESS OF FINISHES
II.
4.4.4
the
difficult
pit.
panel
traces.
TABLE III
is
was too
test
using
The anodic
Alodine
it
was
observing
the
12).
of each
the
each
I
ISpecimen
for
2 ~m and
because
roughness
cross-section
techniques
method
profile
microsectioning
in
be photographing
thickness
film
film
metallographic
suitable
found
Layers.
anodic
normal
most
layer
the
19
T851
are
shown
is
shown
of
test
pieces
to
in
Table
IV.
The
in
an excellent
their
the
Figure
13.
resistance
to
original
30-day
exposure
yellow-grey
to
salt
20
ESA STR-212
RNODiSED
ONCE
RNOOiSEDT\.Ii CE
2
1
0 7- 14 21 30
-
13
-
7
I
I
14- 21 30
I
J
0
exposures
0
I
RNOOiSm TWiCE
(imj;OW mARk\)
Figure
(May 1984)
\JElOfD-
7 14 21 30
Overall
view of test
of up to 30 days.
0
pieces
RLOOiNE 1200
I
4
7
14- 21 30
following
salt
spray (ASTM B 117)
spray.
Discoloration
structura
1 ri b of
pattern
shown
corrosive
in
have
the
there
of
run
5.
attacked
the
from
salt
no marked
It
These
with Alodine
*
1200
of
the
pieces
(Alodine
exposed
side
Corrosion
corrosion
is
test
following
the
waff 1e
absence
the
products
sites
interesting
to
corrosion
of
of
seen
and
slightly
note
that
the
weld
are
first
in
seen
7-day
Figure
13
discoloured
7 days,
after
metal
surface
or
RESULTS FROM TEST PIECES
EXPOSURE TO SALT SPRAY
DAYS
4. Welded plate finished
part
1200)
EXPOSURE
3. Top part anodised
twice; bottom part
anodised once (first
treatment) with
imnersion line
ri bs form
beneath
coated
FOllOWING
2. Anodised twice
directly
the
TABLE IV - VISUAL INSPECTION
1. Anodised once
(2nd treatment)
area
confirmed
preferential
SPECIMEN PANEL
an
Microsectioning
test.
large
surface.
1.
on the
spray
several
to
area.
and conversion
remaining
is
spec i men no.
in this
be partially
period
confined
Figure
attack
b) The welded
to
is
21
- T851
NUMBEROF CORROSION SITES
EXPOSED SIDE UNDERSIDE AlONG SCRATCH
a
7
14
21
30
20 *
>50 *
>50 *
a
a
7
14
21
30
a
a
a
a
a
a
a
a
a
a
7
14
21
30
a
a
a
7
14
21
30
a
10
a
*
a
a
a
a
10
>100
complete
complete
a
a
a
a
a
a
a
1
a
a
a
a
1
1
a
a
a
a
a
a
a
a
2
2
a
a
20
>100
complete
5
complete
complete
complete
a
Only in position
B, under rib (gas bubbles released
during
anodising
had
become trapped
under this
protrusion
and prevented
adequate
build-up
of
anodic layer).
These ribs are part of the core shell panel which has a waffle
structure as shown in Figures 4 and 5.
22
its
heat-affected
zone.
General
surface
corrosion
ESA STR-212
(May
1984)
is evident
after
two
weeks and this becomes a complete surface network after three weeks.
The remaining test pieces which received
a 4-week exposure to salt
spray were seen to be totally
covered in white and dark-grey powderlike corrosion products.
c) The score lines which were made to expose a thin
aluminium alloy
on each of the test
pieces
line of unprotected
were examined after
the test
under a microscope.
As listed
in Table IV minute pits only were
observed within the scratches
of the anodised test pieces after three
weeks of exposure to salt
were readily attacked.
4.4.5
spray.
However, scores
on the Alodined
sample
30 days of salt
spray
Adhesion Test Results
Each of the
pieces
that
test i ng was submitted
had been exposed
to the
adhes i on test.
to
The resu 1ts
showed all
anodic fi lms to have passed this test,
being fully adherent to their
substrates~
The adhesive tape was noted to readily remove the surface
corrosion
4.4.6
products
and remaining
Metallographic
The surfaces
of test
cross-section
are
The cross-sections
parallel
to the
film on the Alodined
sample.
Results
pieces
identified
which contained
features
by the box markings
to be examined in
shown in Figure
13.
of each mounted sample are made in a plane which is
rolling
direction
of the plate
and normal to the
surface which was exposed to the salt spray. Figures 11 and 12 clearly
highl ight the very rough appearance of the surface.
An account of the
mode of pitting
was given in Paragraph
4.4.2.
The chromic acid
excellent
protection
anodising
produced an adherent
oxide film with
even after 30 days of exposure to the salt spray.
The results
in Table IV show the poor corrosion
listed
the Alodine 1200 sample. Although general
surface
apparent on this plate,
no deep pitting
of the parent
observed
from any of the microsections.
Corrosion
cavities
resistance
of
corrosion
was
metal could be
were seen on
-
the
surface
and
and
15).
path
to
of
the
These
weld
metal
corrosion
a maximum
fronts
depth
of
23
T851
its
are
heat-affected
noted
162 ~m after
to
zone
follow
30 days
(Figures
14
an intergranular
of exposure
to the
salt
spray.
It
is
films
likely
that
is
due
to
complex-oxide
the
4.5
4.5.1
the
the
layer
2219 Al
poor
corrosion
presence
and that
of
of
copper
this
will
any
requirement
chemical
conversion
dispersed
prevent
in
complete
the
thin
passivation
of
surface.
Conclusions
In
the
absence
of
resistivity
of
high
Type
it
is
2219,
involving
the
spray
(i .e.
without
strength
that
submission
ASTM-B-l17)
of
for
finishes
This proposal
an
test
will
for
the
of
a)
All
spray tests
of the
in Paragraph
The Alodine
test
method,
a standard
weeks
(336
screen
10-year
particular
salt
hours)
materials
Spacelab
and
life.
Spacelab environmental
4.1,
in
and the findings
agreement
with
of
those
showed:
anodised
surface corrosion
salt spray.
b)
two
suitably
The results
of this evaluation
are
previously reported in the literature.
The salt
to
corrosion
in
accelerated
is based on the existing
requirements,
as outlined
this evaluation.
the
alloys,
samples
a period
corrosion,
protective
defining
structural
suggested
resultant
their
4.5.2
resistance
samples
following
exhibited
resistance
good
a 4-week (672 hours)
1200 samples
did
not
satisfy
the
exposure
to
to
MIL-C-5541
requirements
for chemical conversion coatings (i.e.
7 days salt
spray). General surface corrosion
and crevice corrosion
in the
weld
heat
affected
unrestricted
paint
or resin
zone
Spacelab use.
coating.
renders
It
this
finish
unsuitable
would be a suitable
for
base for a
24
\
.\.
#
.
"\
.
.
A
- As received
(0 hours)
,
"
»
,.A.
.'"
. l P"
"
.'
.t'
\
"
\"'"
~.
B
-
14 days exposure
(336 hours)
adhering
product
\ , >...
."
""
?,,'
(
".r
/:
. ('.'~ .,
...'
...
'~j'
.
. ~ ~ .~
'..,
. . )\ . f/If'
~
-;'"
c.. ~
,~.",'
,\.
,
')
r.
'
;
'"
.
,
J
-.
j t.
\.
.-
i>
/"
,. ,\
.l' \ .
.f.. :.
f
P
'
. , .'w<. . .
I""
.
d
corrosion
. . , '.r
I
'
./
~
.'
'
'\
C
..t
"
,"',
!
",
-
30 days exposure
(720 hours)
Figure 14 - Photomicrographs made in the weld metal of the plate sample
which had received an Alodine 1200 surface treatment.
Depth of corrosion
after 30 days exposure to salt spray is 45 ~m. Micro-structure
is as-cast
divorced Al-CuA12 eutectic
(x430).
,
-
25
T851
'--......
~
A
- as received
I
B
-
.-
(0 hours)
.
30 days exposure
-(720 hours)
Figure 15 - Alodined surface above the weld heat-affected
corrosion after 39 days is 162 ~m (x430).
zone.
Depth of
26
(May 1984)
ESA STR-212
4.5.3
The anodic finish was unaffected
by 100 thermal
-150:>C and 100:>C at a pressure of 10-6 Torr.
4.5.4
The excessive
surface
roughness
Al 2219 sheet resulted
cleaning treatment prior
cycles
of the submitted
between
anodised
from an incorrectly
applied
chemical
to anodisation.
Chemical attack of the
surface had been enhanced by the inhomogeneous distribution
of
undissolved
CuA12 particles
within the microstructure
of the
alloy.
Evaluation
of those
they are considered
5. EVALUATION
OF THE
samples was, however,
to represent
CORROSION
interesting
as
a worst case condition.
RESISTANCE
OF PAINTED
AND CHEMICAL
CONVERSION COATED SAMPLES OF NON-STRESSED AL 2219 WELDMENTS
5.1
Introduction
Following the corrosion tests on Al 2219 described in Chapter ~, it was
proposed that the standard salt spray test method, as prescribed
by
ASTM-B-117, would suitably
their protective
finishes.
for a period
of two weeks (336 hours)
of at least 10 years.
pass this test readily,
from general
weld heat
screen Spacelab
Exposure of test
surface
affected
assess
structural
materials
and
samples to the salt spray
should represent
a Spacelab
life
Whereas anodised Al 2219 samples were seen to
the Alodine 1200 samples were noted to suffer
corrosion
zones.
this
It
designed
to
corrosion
reported
and not the effect
in Chapters 7-9.
and crevice
should
material's
corrosion,
be noted
that
these
susceptibility
of
stress
particularly
tests
to general
corrosion,
which
in
were
surface
will
be
investigation
aimed at studying
two protective
finish
The present
systems which were proposed for the non-anodised
surfaces
present
in
the vicinity
of Al 2219 plate weldments. Ideally,
protective
should be reasonably
transparent
in order that
in-service
inspection may be conducted for flaws,
proposed finishes are: -
including
fatigue
finishes
visual
cracks.
The
- T851
- Alodine
1200,
maintenance
-
brush-applied
routine;
in,mind the requirements
found that
transparent
Cuvertin
paint.
Description
of test
as a
cur i ng protect i ve 1ayer to the
for space materials,
a computer search
001* would be the most suitable
*Cuvertin 001 is manufactured
of Dus se 1dorf.
5.2
to the weld area every two years
App1i cat i on of a room temperature
Alodined weld.
Bearing
27
under licence
candidate
for
a
in West Germany by Henkel
samples
One Al 2219 welded plate (330 x 200 x 7 mm) in the T 851 condition was
forwarded for testing.
This plate had been TIG welded across its centre
line, using a filler
rod of Al 2319. The weld bead had been shaved,
etched,
dye penetrant-tested,
recleaned
and chemical
conversionfinished
5.3
5.3.1
with Alodine 1200.
Preparation
of samples
The welded plate was cut into 9 strips
the weld. The machined
painted
with a liberal
5.3.2
running perpendicular
to
edges of these samples were carefully
coating
of Cuvertin
001 to prevent
unwanted corrosion of these surfaces
to the salt spray environment.
during
The nine
three
Table
V.
samples
were divided
into
subsequent
groups
exposure
according
to
28
ESA STR-212
(May 1984)
TABLE V - DESCRIPTION OF SAMPLES
SAMPLE NO.
*
DESCRIPTION
OF FINISH
1,
2 and
3
*
Control
coating
4,
5 and 6
*
As samples 1-3, but restored
with fresh
Alodine
1200 at 3-days
intervals
during
the salt
spray exposure.
7, 8 and 9
*
As samples
Note:
Samples
Refurbishment
second
converted
free"
Each
returned
to the
Painting
of
001
clear
gun
to
a nominal
at
room
performed
on samples
extremes
hardware.
on the
5.4
Test
The
samples
before
the
until
first,
chemically
a "waterbreak
and
bru sh
Alodine
was
app 1i cat i on
and
is
a treatment
which
provides
to
limits
applying
Cuvertin
cured
the
and
the
was then
vacuum
defined
ESA Specification
100 cycles
to
performed
were
be
to
for
assess
the
for
to
by
effect
of the
applied
purposes
and
was
temperature
chosen
the
7
in PSS-01-702.
encountered
properties
by spray
PSS-01-704
between
temperatures
environments
also
by diluting
The paint
within
corrosion-resistance
s imul ate
Spacelab
of
space
finishes.
Programme
were
any salt
5% salt
exposed
the
corrosion
by
the
50 llm.
of
This
were
after
vacuum.
toluene
3, 6 and 9 for
The tests
out
under
001
20% with
values
thermal
cycled
paper
re-a 1od i ned
+6CP C and -lCP C. These
extreme
all
Cuvertin
abrading
8 and 9 was achieved
thickness
under
with
original
cabinet.
temperature.
Cycling
until
then
paint
outgassing
Thermal
vacuum
7,
by
carborundum
and
spray
polyurethane
acceptable
the
240 grit
s amp 1e was
samples
painted
thermally
periods
obtained
salt
with the
degreased.
4, 5 and 6 was carried
with
was
but
later
inspection
surfaces
removed.
days
samples
third
surface
1-3,
3, 6 and 9 were
of
and
samples finished
of Alodine
1200,
numbered
spray
spray
surfaces
for
exposure
traceabil
ity
(Figure
16).
They
accordance
with
ASTM-B-117
test
in
were
inclined
approximately
were
6
then
photographed
subjected
except
degrees
to
that
the
from
the
-
29
T851
y.,
~",~~,..~,!$>'
.(tj"f'¥.A.
_pI"
Figure
-
16
~;AA$)1h
"h,.;!'tf
~"''''>'\.t~
lir't,c
.~
.'.
'..'~
1"'"
1J~!)
Samples in the as-prepared'
state,
prior
to salt-spray
tests.
2
~
wnw
SM'ltS
AlOOlN£
1200
SNOPlU--
II'.Ift'OIOIIr1
wmt ALCnIHE 1200
noon it:. 1200
c~:n:[J
1t'''H
Qi(}.\,U<lt !Xt
Figure 17 - Samples after 14 days exposure to 5% salt spray test.
(Note
that
thermally
cycled
sample no. 3 has retained
its golden brown
appearance
whereas samples nos. 1 and 2 have faded and are more
corroded)
.
30
ESA STR-212
(May 1984)
vertical.
The panels were inspected before the salt spray exposure, at
three regu 1ar i nterv a 1s dur i ng exposure and aga i n after comp1et i on of
the test.
As suggested
was chosen
accept/reject
in Chapter 4, a 2-week (336 hours) exposure to salt spray
as the test
duration.
The inspection
criterion
for
was that, after the 336-hour exposure, no specimen should
show more than a total of 5 isolated
pits or spots, none larger than
1/32 inch in diameter,
in a total
of 30 square inches.
Areas of
corrosion occurring within 1/4 inch of the edges of each specimen would
be ignored.
On completion of the final inspection,
certain
samples were submitted
to metallographic
inspection.
Microsections
were made across typical
pits
and,
after
polishing
and etching
in Keller's
reagent,
photomicrographs
were taken on a Reichert
projection
microscope.
The
full
test
5.5
Results
5.5.1
programme is detailed
in Table VI.
and Discussion
Thermal Cycling Prior
to Salt
Spray
No samples were seen to have become cracked,
crazed, delaminated
or
otherwise
degraded as a result
of the thermal cycling under vacuum
exposure.
5.5.2
Salt Spray Test
The samples are shown in Figure
inspections
listed in Table VII.
a) Control
samples (nos.
Rapid degradation
1
-
17 and the
results
of the
visual
3)
of the Alodine
1200-finished
samples
results
in
severely
discoloured
surfaces
after
the 14-day exposure.
The
excessive number of corrosion
sites is cause for this finish to be
unsuitable
for the proposed total Spacelab life of 10 years. These
results
confirm the findings of Chapter 4.
-
It
is
interesting
cycling
under
than
the
remained
spray;
samples
colour
after
is
known,
nos.
in
it
this
CONTROL
SAMPLES
(Alodine
1200)
2
3
is
x
from
that
denser
thermal
corrosion
sites
less
This
final
deep
the
underwent
sample
exposure
brown
spray.
to
chromate
by the
salt
straw
for
this
finish
Dissolution
of
chloride
or
ions
is
PLANNING OF TEST PROGRAMME
6
PAINTED
SAMPLES
(Cuvertin 001)
STEPS
7
8
9
1) Preparat
x
x
x
2) Painting
x
3) Thermal
x
x
x
x
x
x
x
x
x
x
4)
x
x
x
x
x
x
x
x
x
5) Salt
x
x
x
x
x
x
x
x
x
6)
x
x
x
i on
Cycling
Inspection
exposure
spray
on day 3
Inspection
7) Restoration
x
x
x
x
x
x
x
x
x
8) Salt
x
x
x
x
x
x
x
x
x
9)
Inspection
x
x
x
10)
Restor
spray
at i on
x
x
x
x
x
x
x
x
11)
Salt
x
x
x
x
x
x
x
x
x
12)
Inspection
x
x
x
13)
Restorat
spray
x
x
x
x
x
x
x
x
x
14)
Salt
x
x
x
x
x
x
x
x
x
15)
Inspection
x
x
x
exposure
on day 7
x
x
a pale
conversion
presence
also
to
The reason
and more tenacious.
film
RESTORATION
SAMPLES
(Alodine
1200)
5
the
to the
assumed
-
3, which
samples.
after
exposure
modified
4
treated)
1 and 2 changed
and has become
of
no.
considerably
colour
3 days'
but
sample
(heat
TABLE VI
1
that
supports
brown
only
is modified
breakdown
vacuum,
non-cycled
deep
not
to note
31
T851
exposure
on day 10
i on
spray
16) Metallographic
inspection
exposure
on day 1
32
ESA STR-212
(May 1984)
- VISUAL INSPECTION RESULTS FROM SAMPLES
TABLE VII
AFTER EXPOSURE TO SALT SPRAY
SAMPLE NO.
EXPOSURE NUMBER OF CORROSION SITES
DAYS
EXPOSED SIDE UNDERSIDE
,
;
ALODINE
1200
1
3
7
10
14
2
3
7
10
14
.,
3
i,
3
7
10
14
>
2
4
50
100 (*)
0
3
7
7
>
3
'5
50
100 (*)
0
3
7
28
0
7
10
50
0
0
2
2
(,
RESTORATION
SAMPLES
PAINTED
SAMPLES
*
70% of
4
3
7
10
14
- 4
6
20
53
0
0
0
3
5
3
7
10
14
3
2
20
58
1
1
1
1
6
3
7
10
14
4
10
20
52
7
3
7
10
14
0
0
0
0
0
0
0
0
8
3
7
10
14
0
0
0
0
0
0
0
0
9
3
7
10
14
0
0
0
0
0
0
0
0
surface
area
covered
in corrosion
'.
0
0
1
3
products
-
markedly
reduced,
unmodified
A1C13
film
corrosion
These
samples
corrosion
visually
more
produced
by the
Painted
the
samples
the
salt
by
of the
The
of
a blend
of
These
are
the
than
the
1 and 2).
are
at
having
Table
bay
cleaned
more
quite
away
so
and
presumably
as
which
is
However,
well,
and any pitting
application
VII).
to
leave
does
surface
a
commence
conversion
confined
to the
areas
7-9).
group
passed
environment
to
the
except
of the
should
test
for
sharp
under
aluminium
alloy
corners
be radiused
as,
otherwise,
layer
of
throughout
underlying
the
that
test,
chromated
unaffected
seepage
noted
thick
and remained
slight
be
sufficiently
transparent
5.5.3
(no.s
It
need
a
(see
1200. The corrosion
due to exposure
section
sites
periodical
in this
paint.
the
weld.
spray
coating
nos.
test
finish,
Alodine
Samples
All
the
the
Al(OH)3'
fai 1 the
corrosion
products
acceptable
and
of
6)
to
the
corrosion
formation
17 (Samples
corrosion
held
by
away from
c)
of
has
because
noted
the
water)
-
4
and
with
in Figure
(nos.
were
refurbishing
in
seen
number
retarded
rapidly
soluble
samples
permitted
dissolution
progresses
products
b) Refurbished
is
whereas
(normally
33
T851
thus
all
corners
they
and
will
paint.
The
facilitating
by
the
edge
through
changes
in
not
be covered
paint
remained
visual
inspection
aluminium.
Metallography
surfaces
of
cross-section
a plane
normal
very
are
which
to
non-exposed
test
is
the
sides
little
pieces
identified
parallel
surface
of
pitting
chromate
conversion
on
to
specimens
the
was
are
Sample
its
finish
contained
in Table
which
corrosion.
shallow
which
no.
underside
was not
VI.
features
direction
exposed
detected
to
the
VII
observed
18)
are
of
in Table
2 was
(Figure
be examined
The microsections
rolling
noted
to
and
by optical
the
salt
spray.
have
to
support
the
made in
plate
to
in
and
The
suffered
thin,
microscopy.
very
intact
The
34
exposed
side
of this
sample was noted to exhibit
19, 20 and 21) in both the parent
pits
they
(May 1984)
ESA STR-212
metal
deeper
pits
and weld pool.
(Figures
Only isolated
were observed on Sample no. 3 which had been thermally
cycled,
were similar
to those shown in Figures 19-21. The refurbished
Sample no. 5 was also noted to support a cleaner surface and, although
pits were observed in cross-section,
they were wide-mouthed, presumably
due
to
Paragraph
protection,
the
intermediate
abrasive
treatments
described
in
5.3.2.
The Cuvertin
001 paint
system
afforded
good
being an effective
barrier
layer of 45-50 ~m. The principal
disadvantage,
characteristic
remain effective
recommended for
are not expected.
5.6.1
systems,
is that
they
will
not
once mechanically damaged. Their use is therefore
only
applications
where considerable
traffic
or abrasions
Thi s paint
Alodined plate finish.
to cause micro-crazing
5.6
of paint
can be seen to have adhered
Thermal cycling and salt
of the cured paint.
we11 to the.
spray were not observed
Conclusions
The results
indicate
that non-stressed
Al 2219 weldments are
best protected from general surface corrosion by a paint system
applied to a chromated aluminium finish.
The recommended paint,
Cuvertin
001, is acceptable
from an outgassing
remains
optically
transparent
environments.
This will facilitate
the welds.
point
of view and
after
exposure
to the test
periodic visual inspection
of
5.6.2
As reported in Chapter 4, the Alodine 1200 again failed to pass
the 14-day exposure to salt spray. It also failed to satisfy the
MIL-C-5541 7-day exposure to salt spray.
5.6.3
Although the "restoration"
treatment
failed
the test
programme,
this system may be suitable
for easily accessible
non-stressed
weldments
on Spacelab.
Possibly,
after
careful
visual
inspection,
a decision
to refurbish
flight
hardware might be
approved, thus permitting
removal of corrosion products, Alodine
and pits by abrasion,
followed by the re-application
of fresh
Alodine 1200. Figure 7 illustrates
the location of some easily
accessible
weld zones.
-
- T851
Figure 18 As-polished
section showing the underside surface
sample no. 2 At this magnification
the exceedingly
thin
chemical conversion finish cannot be detected in cross-section
35
of Alodined
«
0.2 ~m)
(x400).
Figure 19 - As-polished section of the exposed face of Alodined sample
no. 2. Pits are noted to be 15 ~m deep (x400).
36
..
..
'
<,)'.
.
..
~
~"4
~
"'
Figure 20 - As in Fig. 19, but etched with Keller's
grain structure in a region of the parent metal. Pits
reagent to reveal
have a depth of 12
JJm(x400).
,
i
,
,-.~7!:':::. J ',', \ . -, .
,~,r
'~-,
t
11,
,"""
<.
..~
\
'~,'
~">,
(x400).
.
-""',,.-;.
,,;',
-y. .~-~
"""
,-
,,<"
?
\
i ~.
..
Figure
)
,'"
-, ~ .'"
\, ),' /~o
.-';;
4...'\. ,
'\
21 - As Fig.
,
~
J
.
~
. .'
:.. ~ 1-"..
'l.
¥
20 but in weld pool.
Pits
have a depth of 10 JJm
- T851
2219
37
6. INTERGRANULAR CORROSION TESTING OF WELDED PLATE
Introduction
6.1
A rapid
test
to
assess
intergranular
corrosion
Test
Std.
Method
Specification
of
Incorrect
the
observed
Test
The
samples
can
the
be
test
of
large
and
provide
the
identified
in
Military
as to
structure
welding
to
in Federal
U.S.
of
that
particles
exfoliation
of
the
the
2219.
schedules
intermetallic
if
alloy
a control
grain
undesirable
CuAlz
2219
is detailed
822.1)
within
and
welded
stress
will
content
of
along
surface
is
exposure.
consisted
of
procedures
pre-etched
in
with
2219-T851 plate TIG welded
2319 filler
alloy.
Each sample
to
4 mm thick
an
a so 1ut i on
condition.
made up of
Al
of
Samples
sod i urn hydrox
were
i de
then
immersed
dissolved
in
to
produce
in
a corrosive
was
a un i form
medium
:
57 g
Sodium
10 ml
Hydrogen
1 1
Distilled
The temperature
After
test
of
Procedure.
standard
was
The
formation
after
6.2
time
(method
treatments
boundaries
surface
1516
copper
solution
grain
absence
no.
the
susceptibility
in the
MIL-H-6088E.
homogeneiety
promote
the
chloride
peroxide,
water.
of the
corros
i ve med i urn was 30
0
C
!
5
0
C and immers i on
6 hours.
exposure
the
samples
were
to ascertain
metallographically
visually
whether
examined
or
not
and
then
intergranular
prepared
corrosion
had occurred.
6.3
Results
No intergranular
of
these
samples.
corrosion
Very
metal well away from
was found
slight
pitting
to
have
corrosion
the weld pool and its
taken
place
appeared
heat-affected
in
any region
in the
zone.
parent
(May 1984)
ESA STR-212
38
6.4
Conclusion
From
these
findings
performed
7.
it
was
assumed
that
the
welding
had
been
correctly.
METALLURGICAL EXAMINATION OF 2219-T851
PLATE) AFTER STRESS-CORROSION TESTING
7.1
process
IC'
RING
SAMPLES
(THICK
Introduction
Stress-corrosion
Alcan
Booth
tests
Sheet
Ltd.
been machined
from
105
test
mm.
The
constant-strain
in
up
75% of
for
Although
only
rings
three
the
0.2%
these
plate
under
required
30 days.
two
still
intact
plate
size,
from
each
7.2
Materials
7.2.1
on the
were
carried
of different
consisted
each
proof
out
fifteen
of
which
G38-73.
stress
2219
aluminium
alloy
by
on samples
which
had
thicknesses,
of
ASTM Method
as
i.e.
'C'
rings
was
stress
The stress
determined
35,
and
three
corrosion
levels
in
80 and
the
were
set
transverse
thicknesses.
exposure
test
The constant
out
specimens,
with
cracks.
were
plates
a 30-day
remained
tests
samples
accordance
direction
carried
The
tension
tested
at
were
for
strain
to
48 days
tension
Eventually
testing
was the
without
after
have
86 days.
been
developing
specimens
one specimen
submitted
were
broke
Three
requirement,
of
after
IC'
to ESA for
'C'
stress-corrosion
all
the
the
unbroken
after
69 days,
the
ring
the
other
samples,
one
examination.
Details
Cast Analyses (weight per cent)
PLATE SIZE
(mm)
Cu
Mn
Mg
Fe
Si
Zn
Ti
Zr
V
80 & 105
6.3
0.28
<0.1
0.12
0.07
0.03
0.07
0.14
0.09
35
6.5
0.28
<0.1
0.12
0.07
0.03
0.07
0.14
0.09
-
CORROSION PROPERTIES OF A1 2219
7.2.2
Heat Treatment
Pre-heat
for ro 11i ng
Solution
heat treatment:
Control
: 24 hours at 500-52c? C.
<63 mm4 hours >63 mm8 hours at 530-54c?C.
Stretch
Precipitat
: 1
ion treatment:
-
Tensile Properties
I
IP1ate
Size
Test Direction
I
I
I
I
I
I
I
(mm)
I
I
I
80
35
I
7.3
Stress
Transverse
I
II
I
I
374
I
I
I
I
I
I
I
454
8.5
I
462
9.0
I
474
I
10.0
I
Method of Examination
Samples were cut from each of the three
clear,
I
I
I
II
%
I
I
348
I
I
(N/mm2)
(N/mm2)1
362
Elongation
UTS
I
I
I
105
%
0.2% Proof
I
I
2
18 hours at 172-17]0 C
7.2.3
I
39
T851
cold-setting
and then mounted in a
epoxy resin.
The mount was ground and polished
a Reichert
conditions.
IC' rings,
projection
The etching
to a 0.25 ~m finish
microscope
was carried
HF
1. 0 m1
HN03
2.5 m1
HC1
1. 5 m1
H2O
95.0 m1
then examined under
in both the polished
and etched
out with Kellar's
reagent,
i.e.
The resulting
'smutting',
common with alloys containing
copper, was removed in a 50% solution of nitric acid.
large
amounts of
40
7.4
Results
7.4.1
Metallography
present
revealed
on
any
difference
size
7.4.2
in
to
that
generally
pitting
that
instances
was
mainly
7.5
Conclusions
From
this
required
corrosion
probable
in section
is
resistance
takes
that
the
the
rather
on tension
form
than
the
one
the
corrosion.
corrosive
with
and compression
(See
Fig.
clear
only
plate
On the
attack
faces
only
was
exhibited
occasional
that
stress-corrosion
failure
an intergranular
faces,
occasional
the
attack
instances
of
24).
the
2219-T851
cracking.
of predominantly
ultimate
of
Compression
with
quite
to
from
obv i ou s
pits.
attack
it
no
were
example.
laminar
transcrystalline,
evidence
was
attack
stressing
predominantly
both
intercrystalline
corrosive
pitting.
cracks
there
a typical
tensional
of wide-based
th at
aspects
wide-based
was
samples,
the
various
under
of
of
stress-corrosion
and
22 shows
detail
that
s amp 1es
extent
Figure
were
no
that
the
the
23-25
On all
of
another.
Figures
faces
the
(May 1984)
ESA STR-212
transcrystalline
condition
would
weakening.
alloy
possesses
Also,
since
pitting,
be due to
the
it
a reduction
is
-
41
T851
~
~ ~
H
~
>1
~
Q
@
U)
Figure
plate.
22 -x 11 cross-section
of "C" ring
manufactured
from
35 mm thick
42
ESA STR-212
Figure 23
-
As Fig.
22 but
Figure
24
-
Example
of
intergranular
corrosion.
(x4000).
Figure
25
-
Example
of transgranular
corrosion.
(x400).
etched
to reveal
microstructure
(May 1984)
(x45).
8.
METALLURGICAL
EXAMINATION
(LARGE FORGED RINGS)
8.1
- T851
43
OF 2419- T 851
AFTER STRESS-CORROSION
ROUND TENSION
BAR SAMPLES
TESTING
Introduction
(SCC) tests
Stress-corrosion-cracking
on samples
have been performed
of
2419 aluminium forged rings in the T 851 condition. This material was
produced and tested by Thyssen HenrichshUtte.
The test method followed
ASTM specification
G38-73 (for C-rings), stress consideration,
stressing
methods, machining, surface preparation
and inspection being as specified
although round tension bars were employed instead of C-rings.These
tests
were performed on six samples from the remainders of the three Thyssen
pre-production
rings. These 4 m diameter rings were the largest to have
been made in Europe from a high-strength
aluminium alloy.
The stressed
to alternate
solution
duration
test
samples were subjected
immersion in a salt
151b for an agreed
according to Fed. Test Method Std. no.
of 30 days. No sample failures were noted after
30 days and
after
an extended
period
the exposed pieces
were taken from
environmental
chamber and submitted to ESA for metallurgical
analysis.
8.2
Materials
8.2.1
Data
Chemical Composition
RING No.
3580
256
2814
Spec.
Limits
are
the
2219
2419
5.8
5.8
COMPOSITION PER CENT
Mg
Zn
Ti
Cu
Si
Fe
Mn
6.4
6.8
6.8
0.07
0.08
0.08
0.13
0.16
0.16
0.29
0.31
0.31
0.01
0.01
0.01
0.03
0.04
0.04
0.08
0.07
0.07
0.20
0.15
0.30
0.18
0.20-0.40
0.20-0.40
0.02
0.02
0.10
0.10
0.02-0.10
0.02-0.10
- 6.8
- 6.8
CHEMICAL COMPOSITION OF RINGS AND SPECIFIED
V
Zr
0.10
0.09
0.08
0.14
0.13
0.13
0.05-0.15
0.05-0.15
0.10-0.25
0.10-0.25
VALUES
44
ESA STR-212
8.2.2
-
Heat
Treatment
: 430-39CPC (roll
Forging temperature
- Heat
: Solution
treatment
forging).
heat treat,
Quench time,
533°C ~ 5°C (10 hours).
90 seconds.
Quench medium, water.
Cold stretch,
2-3%.
Precipitation
harden 175°C
8.3
8.3.1
Experimental
Stress
(May 1984)
+5°C
(30 hours).
Procedure
Corrosion
Cracking
(SCC) Test.
Round tension bars were machined from the six samples (two samples from
three different
locations)
taken from the three pre-production
rings. The
machined specimens, having a 6 mm diameter, were stressed
perpendicular
to the grain flow of the forged rings, and held at a constant strain.
The
specimens
were stressed
to
which is 75% of the material
for the applicable
thickness
of 262 N mm-2 (i.e.
The stressed
a level
as defined
in ASTM-Method G38-73,
yield strength
in the tangential
of each ring; this was determined
196 N mm-2 perpendicular
to grain
specimens had been exposed to a solution
direction
to be 75%
flow).
of 3.5 percent
NaCl
for a duration of 30 days by alternate
immersions of 10 minutes in the
solution
and 50 minutes out of the solution
(according
to Fed. Test
Method 151b). No failures
occurred
after
30 days, so the test
was
extended providing for a total
exposure
after 39 days, another after 75 days.
8.3.2
Metallographic
The as-tested
photographed.
they were:
of 80 days.
One sample failed
Examination
specimens were removed from the corrosion
rig
and
Two samples were submitted for metallographic
examination,
a) Sample fractured
after
39 days.
b)
No fracture
on removal
8.4
8.4.1
after
from
The
45
exposure
under
load,
but
this
sample
by
the
broke
device.
environmental
test
laboratories
showed
successfully
completed
The first
in the
electrolytic
or
insulation
between
The
after
solution
test
have
No
shown
cracks
into
CuA12
during
that
paths
fo 11 ows
both
of
particles
metal.
forging
relationship
be
of
The
were
to
is
was
visually
be masked
expected
by
to be a
this
to
to
the
the
present
heat
to the
during
massive
of
80-day
network
dissolve
up
and
CuA12 particles.
of
part i c 1es
shown
to
up by
the
high
completely
These
redistributed
in a displaced
result
boundari
network
of
from
es
the
pitting
treatment.
solidification
their
of
that
are
to
were
pitting
structure
fact
solution
grains
SCC
localised
owing
exist
during
elongated
to
which,
broken
the
to
inclusions
the
they
that
grain
unable
been
but
treatments;
to
coarse
was
formed
failed
the
large
no doubt
fine
the
CuA12
alloy,
treatment
39-day
attributed
highlights
of
show the
was confined
unrelated
Most
have
originally
and
could
solid
forging
The
which
identical
adj acent
saturated
had
lack
The test
samples
28-31
as predominately
content
the
the
fixture).
surfaces
film
Figures
attack
were
samples.
light
the
in
32 clearly
Figure
copper
to be due to
by
test
30
alternate
exposure.
failed
grey
which
pitting.
corrosion
the
a microstructure
and laminar
polarised
75 days'
all
a light
The corrosive
within
the
total
this
caused
26 and 27 show these
identified.
ion
believed
after
and A1C13.H20.
sample
corros
T 851 condition
39 days'
and
after
of
debris,
sections
material.
sample
Thyssen
no failures
after
corrosion
occurred
The cross
The
in the
(i.e.
(Thyssen
bimetallic
of A1203
sample.
SCC test
occurred
surfaces
corrosion
to
AA 2419 Alloy,
the
NaCl
Figures
mixture
the
performed
80 days.
fracture
identical.
the
that
fracture
stopped
results
failure
immersion
following
8.4.3
T851
Results
days).
8.4.2
80 days'
clamping
-
2219
the
cast
subsequent
have
1 itt
1e
ESA STR-212
46
(May 1984)
8
!~/.:p
FlA<. T",fE'j)
S,
)A"f
\4N)~t-
lo~,»
E1-.POS~~E'.
Wi
tll,
A<.T"«.t
€-Xl'os,,:,I..£
5fCc.tC,EN
nOM
Figure 26
Figure
27
-
-
Fracture
Af:,'E(.
Ii tii~
'-\Nj)Et't..
~(\)\(E:
ON
g f>
)I\y
LoA})Il£MOVf'\L.
CI.AM'P.
Exposed specimens, as received from Thyssen.
surface
of sample which failed
after
39 days (x12).
Figure
-
T851
28
-
47
As polished.
'". .
r. .. ...
~
<.
,-
-'
'..
>
~.""'"
,
.,.
.
~
}
.
,
.
)
29
-
Detail
..
,N
"
.
]..
from Fig.
..
...
,..,.
J',
J
Figure
..
28 adjacent
. ~
to fracture
MICROSTRUCTURE OF 39 DAY SAMPLE
surface
(x125).
48
(May 1984)
ESA STR-212
Figure
.-,
30
-
- As polished
.'
'f
80 days sample.
..
~.;
~"
#..
h
"
jJ,
Figure 31
(x125).
-
,:'
J..'
As Fig.
,/I
~.
''',
;.
..'
:
,~
Y'
II
~,
(x12).
r
1
':I:~
30, but etched;
...
'~
. ....
"'"
showing general
pitting
corrosion.
. CORROSION
..
PROPERTIES OF Al 2219 - T851
49
,r
-# .....
~?t
,
..
'~
JI'
.".
.A
,1
~
.
'If
y.
,.~
-
_.
]I::
,/
~
B
Figure
32 - Detail
from
39-day
sample
near
fracture
polarised
light.
The colour
photograph
(8) reveals
the
inclusions
as bright
orange.
surface
arrowed
using
CuA12
50
In salt
solutions
these
particles
causing
the surroundinq
mechanism (i.e.
CuAlz is
alloy matrix).
The test
critical
pitting
sustained
8.5
8.5.1
will
behave as minute
cathodes
material
to corrode
by a galvanic
electro
positive
with respect
to the
samples will
naturally
fail
once a
depth is reached
by the remaining
and the applied
cross-sectional
stress
cannot be
area.
Conclusion
Aluminium wrought alloys
are most susceptible
to stress-corrosion
cracking when stressed at right angles to the direction
of working
(i.e.
in the short transverse
direction).
This is probably because
more
grain-boundary
cracks
propagate
area
of
come into
machined so as to expose this
8.5.2
The results
of this
test
the
play.
elonqated
The present
most susceptible
along
samp1es
grain
which
had been
direction.
show that AA 2419 in the T851 condition
is essentially
immune to stress-corrosion
conclusions were drawn in Chapter 7 for plate
8.5.3
grains
The long-term mode of fai lure of these
result
from
microscopic
galvanic
copper-containing
intermetallic
particles
crackinq.
material.
Similar
samples is assessed
to
corrosion
between
and the alloy matrix.
-
2219
51
T851
9. STRESS CORROSION TESTING OF 2219-T851
9.1
WELDMENTS
Introduction
Welded
samples
weldments.
that
all
were
made
in-line
Identical
materials
destructive
tests
representative
of
flight
with
and process
made
on
hardware
Chapter
concerns
various
forms
of
short
transverse
the
first
were
used
to ensure
samples
would
yield
results
those
The
work
stress-corrosion
welded
2219-T851
production
parameters
material.
constant-load
Spacelab
reported
testing
alloy
made
in
carried
to
this
out
standard
on
company
practices.
Unwelded
over aged AA 2014) were
alloy
susceptible
control.
A
The samples
2219-T851
to
specimens
performed
corrosion
assigned
2219-T851
filler
AA 2319,
weld
Processes
were
those
in Fig.
As
A,
but
with
no post-weld
bead
had
as a
for
the
a matching
heat
treatment
been
machined
off.
modular
pressure
shell
Pass TIG welded
repaired
Metal
matching
before
according
was removed
followed
removal
of
from
by further
to
initial
a
standard
weld
TIG passes
pool
with
a
filler.
Single
pass
plate.
The process
the
be used
bead.
by machining,
2219-T851
to be an
1.
Double
practice.
J
could
7 mm plate
with
The
slightly
codes:
TIG welded
applied.
to
was thought
that
following
pass
weld
C 2219-T851
the
As A, but
as this
and one
Single
shown
B
in parallel
stress
were
BS L93 (equivalent
from
Igloo
electron
structure
beam
procedure
shown
(EB)
welded
was that
in Fig.
2.
5 mm thick
employed
for
52
E
(May 1984)
ESA STR-212
BS L93
90
thick
mm
transverse
S1.
BS L 93
The welded
proof
samples
stress
25% and 75% of the
transverse
samples
to be tested
Procedure
The
general
test
PSS-01-737
specimens
to
a
60
short
mm2
cross-
a 36 mm2 area.
level
of 75% of the
be stress-corrosion
of this
follows
of
in 3.5% sodium
provide
tested
material
control
a
basis
tested
for
alloys
susceptibility
is
assessed
the
specimens
of
metallographic
specimens
to
corrosion
or
in Figures
d imens ions
of the
flat
carried
over
0.2%
at 15%,
in the
short
by
out
were
thirty
tensile
tests
Metals
to the
from
stress
of
exposure
same environment
in
the
test.
the
unstressed,
stressed
corrosion
independantly
immersion
hours)
compare
and
Stress
stress-corrosion
days
to
to
alternate
(720
stressed
microsections
occurring
of
assessing
survive
between
ESA specification
under
exposed
in
exposed
in
a thirty-day
comparison
of
distinguish
pitting
were
that
examination
detailed
Susceptibility
specimens
of
strengths
that
the
chloride
susceptibility
SAMPLES
were
The tests
Unstressed
sizes
having
at a stress
stress
procedure
Crackingll.
conditions
The
having
in
as supplied.
IIDetermination
Corrosion
shown
taken
direction.
Test
to
As E, but
0.2% proof
9.2
period.
area.
weldment
The BS L 93 unwelded
Samples
direction
sectional
were
of the
plate.
residual
and
intergranular
The test
rig
33 and 34.
of
the
stress
as-rece
i ved
corrosion
GAUGE LENGTH
(mm)
plate
samp 1es
specimens
determi
by
and unstressed
and
stress.
The
ned
the
overall
which were:
WIDTH
(mm)
THICKNESS
(mm)
END SECTION
(mm)
A, B, C
50
10
7
50 x 30
J
50
5
5
50 x 25
E
28
10
6
30 x 25
ST
28
6
6
30 x 25
is
-
53
T851
I
I
I
Figure
control.
33 - General
Test facility
view
of
is at the
stress-corrosion
tests
and
BNF Metals
Technology
Centre.
unstressed
54
. Figure
load
ESA STR-212
34 - General
stress-corrosion
photograph
testing
(May 1984)
showi ng 1aboratory
set-up for constant
at the BNF Metals Technology Centre.
55
CORROSION PROPERTIES OF Al 2219 - T851
The
average
at
proof
0.2%
of three
tensile
the
stress-corrosion
which
reference
values
specimens
to
corrosion
test.
The
of
tests.
tensile
be tensile
loaded
in
ESA PSS test
for
the
stressed
corresponding
at
by
The
of
with
on
desiccator.
metallographic
were
samples
be
of
conducted
and
day
removed
removal
from
all
were
then
in
the
in accordance
with
stress-
specimens
to
the
automatically
together
with
salt
environment,
the
were
the
washed
in
of the
salt
and corrosion
air
and
stored
tested
and
subjected
warm
tensile
with
in the
specimens
most
provide
according
then
to remove
dried
days
was recorded
period,
stresses
comparison
in triplicate,
failure
After
for
an
from
the
springs
were
sample
establish
thirty
out
to
were
examination
to
calibrated
scrubbing
They
would
surviving
They
type
and elongation
carried
thirty
gentle
The
tests
sample.
the
them.
values
time
samples.
end
warm water
9.3
tension
unstressed
the
products
were
each
These
after
tests
procedure.
for
strength
tested
stress-corrosion
being
and
was established
stress
the
ESA PSS test
in
a
to
procedure.
Results
9.3.1
Results
Specimens
loaded
A8,
to
specimens
5 and
AI,
'Type
9 and
75% of
6 were
specimens
for
set
occurred
tested.
in
proof
i.e.
during
115
the
unstressed
had not
test
tensile
in
kgf
period.
jigs
tensile
mm-2).
No failures
specimens
tensile
corrosion
obtained
controls.
test
2219 Specimens.
stress
N mm-2 (11.7
30-day
been
the
stress
control
The broken
A4 and A8 which
fitted
average
3,
Pass TIG welded
up as unstressed
A9 and 10 and the
tensile
10 were
the
2 and
AI Single
tests
of
the
The stressed
together
tested
were
then
Table
VIII
and
on
Specimens
A4,
loaded
specimens
A5 and A6 were,
specimens
and
therefore,
with
specimens
metallographically
examined.
The
full
results
photomicrographs
were
observed
affected
zone
are
shown
given
in
in any of the
(HAZ)
or the
Figures
in
35 and 36.
specimens,
parent
plate
either
material.
the
samples
No stress-corrosion
in the
weld
pool,
and
cracks
the
heat-
56
(May 1984)
ESA STR-212
-Ie
ee
00
.~.,...
V)
I-.J
:::>
V)
w
c:::
IV)
w
Iz:
a
......
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ex:
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LC)
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c..!J
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co
ex:
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a
c:::
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a
c:::
c:::
a
u
I
V)
V)
W
c:::
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ex:
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c:::
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:::> :::>:::>
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:::>
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w
c:::
~.......
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000
c. c. C.
X xx
Q)Q)Q)
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c..!J
z: z:
00
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c:::
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ex:LC)
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NOO
o:::t .-t
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Iz:
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~.-t
o:::t LC) \.0
ex:ex:ex:
ex: ex: ex:
- T851
57
..."...
Figure 35a)
surfaces.
-
Sample A4 unstressed
control
..,-~..
showing general
pitting
over
'\"
Figure
35b)
- A4 as
polished
in HAZ, general
exfoliation.
---.---------
Figure 35c)
exfoliation.
-
A4 as polished
(x29).
in parent
metal,
general
pitting
and some
ESA STR-212
58
(May 1984)
..~.
""~,,,...
'.
~
.~.~~-,.;~
~.
~..-::'~~'." )- ." -,- r '- :'-.
~.. -~.. .~,/~."~.~
I> F
""..
. ., ,.
-
"
.,..
~""~~~'::".:'~i-~:}
.
"
..
..
.'"
. .~
iIt
-'
. f.-..""
: ..""- ...'
.~-:.
, '.
.,\.
/ ",,A.'
- -
:.
,'.. "
'.
.::-~'~:
~
.
~
t,~: .
...
.,..,.,.,.
"
.,..
.
~~~~
~\.~'.
';"~'''V~ ,.y.~"
.:1"'-"'''-~~:'"
=r~
-
\
~
.-'.-"
...
~
..,' . .'.
"'" ..!.#._~
'"
-.
'. . . -
I' ~,'"
4>
...-
. ",
.r
".
A4 worst intergranular
corrosion
and exfoliation
Figure 35d)
to weld pool in HAZ, maximum depth is 208 ~m. (x120).
~"
~
. ,I ". '..
~
-;
.. .
adj acent
..
.~.
.
'.....
.,I
~
,
,"
'....
~ .--:
,. " . ..~
-
Figure 35e)
~m (x120).
A4 worst exfoliation
.' ~J.'
,,,.
.
-
in parent
;,.. .':-"
... .
..
:-'. ... ..'"
. ...
;.
'
meta1, maximum depth
".
is 430
-.
-
59
T851
J
,. ~. .
.:
..;r I~ ",'
,
"""!,:l:'''':':
~,-~
Figure
36a)
pitting
over
- Sample
surfaces.
A8.
Stressed
corrosion
sample
.'
,:f,
J.
.: 1','
/
"''''oi;
.', .
.'-f"'. .. ...
showing
,,
Figure
36b)
-
A8.
Pit
and intergranular
crack
in HAZ.
(x29).
Jf'
. .
Figure
36c)
-
A8.,Pit
and intergranular
crack
in HAZ.
(x29).
general
60
'.
, .,
- .
"-
...
.) -
(
. '.", ---~
A8. Deepest pit
Figure 36d)
llm. (x120).
- ..-.
..
. ..
,
' ..
- ~.
~...~..
.
""
..
~ 'io
~ "'~'
C"
>
..
-,.:--:
'"
.
-
'.->s.. .
Figure
36e)
"
('"
...
"
,.;
to weld pool.
.
.. .". ..
.. .
"
A")"':~.,-".
,
_:
.'
t"
~'.-,.,
~~:~;-.,-.:..,..."3 -:..~."
. ,
,'rO'
'.
,""'" '\.,1
" "':
<. .
'.."
c-., .
.."
-. ""..
-.- ..'~' '.,' '#
Depth is 542
,
-,
,
~-':'
.-
'..
~.'-
t,,!,,',.#o
.-
,
in HAZ adj acent
.
~
- A8. Deepest pit in parent materials
~_.
..
- :'.,..... . ,
is 208 llm. (x120).
9.3.2
Results
The
stress
the
stress-corrosion
See Table
level
for
'Type
at
specimens
61
T851
B1 Double
was held
IX and Figures
-
Pass TIG welded
112 N mm-2 (11.4
occurred
2219 Specimens.
kgf
during
mm-2).
the
No failures
30-day
test
of
period.
37 and 38.
.,<,.
Figure
depth
37a) - B4 worst
is 192 ~m. (x120).
Figure
37b) - B4 worst
364 ~m. (x120).
intergranular
exfoliation
corrosion
in parent
seen
metal,
in
the
HAZ,
maximum
depth
maximum
is
62
ESA STR-212
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38a)
intergranular
Figure
-
63
T851
B8, Adjacent
to weld
pool
corrosion in HAZ is 375 ~m. (x120).
the
depth
maximum
of
,.
Figure 38b)
(x120).
-
B8. Exfol iation
in parent
metal
has
depth
of
280 ~m.
64
9.3.3
ESA STR-212
Results
for
(May.1984)
'type C' Repair Welded 2219 Specimens.
The stress
level was held at 123 N mm-2 (12.5 kg mm-2). No failures
the stress-corrosion
specimens occured during the 30-day test period.
See Table X and Figures
39 and 40.
TL
TR
BL
BR
Figure 39a) - Sample C4. Unstressed control
reveal positions
of weld pool and HAZ.
TL = TOP LEFT
BL
= BOTTOM
of
LEFT
sample sectioned
TR
BR
= TOP
(x6.5)
to
RIGHT
= BOTTOM RIGHT
~
Figure 39b) - Sample C4. Detail
Depth is 250 ~m. (x120).
of corrosion
pit
present
in weld pool.
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T851
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66
Figure 39c)
intergranular
-
Sample C7. Detail from Fig. 39a) Position TL. Worst case of
cracking in parent metal. Depth is 166 ~m. (x120).
TL
TR
BL
BR
Figure 40 - Sample C-4, stress-corrosion
positions
of weld pool and HAZ. (x6.5).
TL = TOP LEFT
BL
=
BOTTOM
LEFT
test
piece
TR
BR
sectioned
to reveal
= TOP RIGHT
= BOTTOM RIGHT
-
9.3.4
Results
The
stress
the
stress
See Table
for
level
corrosion
'Type
JI
was held
Single
at
- Sample J7,
of weld pool.
Figure
position
41
Figure
reveal
42 - Sample J7,
position
of weld
Pass
EB Welded
136 N mm-2 (13.9
specimens
XI and Figures
67
T851
occurred
during
2219.
Kgf
the
mm-2).
30-day
No failures
test
of
period.
41 and 42.
unstressed
(x6.5).
stress-corrosion
pool.
control
test
test
piece,
piece
sectioned
(x6.5).
to reveal
Sectioned
to
68
(May 1984)
ESA STR-212
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9.3.5
Results
for
The 75% of 0.2
(25.4
Kgf
proof
are
presented
E and STI Short
stress
All
stress
Metallography
and the
proof
mrn2).
0.2
'Type
samples
failed
samples
BS L 93 alloy.
(ST 1 to 3) were
the
30-day
period.
survived
the
30-day
test
XII.
revealed
stress-corrosion
stress
transverse
within
in Table
25% proof
69
T851
samples,
cracks
as shown
-.
held
The
at 249.5
N mm-2
25% and
15% of
exposure.
to
exist
in Figures
in
The results
both
the
75%
43 and 44.
.';'
~
. ",'~."
,-
... :.,
'-","
~.,..~
~
~-
"
Figure
( x50 ) .
43a)
-
Pit
at
surface
with
---
SC crack
.....
.,.,
-.r~
.
t'~~
Figure
43b) - Detail
of tip
of crack
below
from fig.
(sample
.
'it'
--"'"
43a.
(x500).
ST1,
75% PS).
V)
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0
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(May 1984)
ESA STR-212
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~V)
LLJ
0::
z: I::
00
-.J
LLJ
V)
N
I
~oo:t oo:t oo:t oo:t
V)
LLJ
.........
z:
-.J
c(
U
V)
......
:I:
U
LLJ
.
E
~E
N"""'"z:
::E
0
. . .
N LO oo:t
X
LLJ
-.J
ex:>
c(
. .
:::SN LO
oo:t \0
o..M M
+J
. . . .
oo:t \0 r--. N
MNMM
MMMM
. .
Oor--.
I:: 0...-4
\0 \0
MM
I
/\.
-
1::=
(])
r.,...
~VI
I::
(])
-. .
0'1 oo:t
:::s \0...-4
N LO
o..M N
+J
-
r--tex:>
0.. \0
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+oJ
~"C
.
0'1...-4
1::= =
.""
0
0:
I::
I::
4-=
I
I
I
1'0
(])
LLJLLJLLJc(
>
"1'0
1'04(])
~+J
1'0 0
I::
I::
1'0
=
0
.,...
II
+J
u(])
VI
I
VI
=>
oS:;
+J
0)
VII::
-..
oS:;oS:;
0
N
0
N
LO oo:t N
MO
0)
..................
0)
-
u=
r--.
V)
.........
a..
r-
~0
~LO
N
.........
=
1::=
(])
+J
1::
0
=
u=
-
a..
+J
VI
I::
=>
U
V)
+J
VI
I::
=>
oo:t LO \0
ex:>0'1 0
~...-4
oo:t LO \0
r--. ex:> ...-4NM
LLJ LLJ LLJ
V) V) V)
V) V)
0..
~VI
"0
(])
VI
VI
(])
LLJ LLJ LLJ
u=
0
0'1...-4
V)
0
"0
~"C.,...
1'0 VI
oS:;+J
+J
VI
I::
=>
U
V)
(])
+J
I::
"0
(])
VI
VI
(])
u
(])
0..
~VI
~r-
\O(])
o
=
E
.,...
V) V)
u
r-
~0
~LO
r--.
.........
1::=
(])
O(])
oo:tLO
V)
(])
0)
.-jNM
.
::Er-.,...
ex:>...-4
oo:t oo:t
MM
(])
r.,...
E
.,...
u(])
U
~V)
...-4 .-j
I'O(])
:::sr--.. uV)
"0
(])
VI
VI
(])
0..
VI
=
.
oS:;
~0
=
r-
r-
I
+J =
VI
(])
+J
.
oS:;
+J
I::
0
E
.,...
u
(])
(])
I:: oo:t N
MM
I
r-
LO
.-j
=
0 ...-4. ex:>.
r--. M
.........
a..
=
+J
r--.
V)
.........
~+J
VI=
(])
+J
z:
r-
0..0
N
\0 r--.
MM
0..
VI
z:
LLJ
::EO::
...... LLJ
U c:c
LLJ ::E
a..
~~~~~~~~~~V)
=>
r-
"0
(]) ...-4
(])
M
r--. r--. r--. r--.
MMMM
U
(])
a..
......
0::
u
V)
LLJ
0
"0...-4...-4
r-OO
E
......
iC
"CNN
(])
:::SOO
.,...
......
. .
I
I
~0'1r--. M 0
I::
~~(])
z:
0
......
/\.
~r-
...-4 oo:t oo:t \0
a..N
z:
c(
"0
iC iC
(]) ...-4...-4
r-
.
E
~~E
~~0..
VI
(])
~+J
V)
41'0
I
~......
~O
~c(LO
V)
1'O:::s
0
oS:;
N
V) V)
:::s
.
VI 00)
I::
I::
(])
a.r,...
E~~
.,... ou
U
~I'O
(])..c~
~0..
U
VI I::
(])O
LLJ EI::
.,...
~Ull
~(])
1'0 0.. U
::E V) I::
iC
-
T851
71
1',.~\
~,'''''''-''[-z'
/>
,
~
"
.0
,.!.,',-'-,
,
...;.',J..
~
..
;:.
Figure
(x50) .
-
44a)
Pit
at
surface
with
'''''",¥
~~'",
SC crack
below
(Sample
ST4,
25% PS).
stress-corrosion
and
~~
~.
f
"..
".
Figure
9.4
44b)
...
- Detail
of tip
of crack
from
Fig.
J/'X'
'*
44a).
(x500).
Discussion
9.4.1
Welded 2219 Alloy
The results
of the
unstressed
control
corrosion
cracking
failed
strength
during
of the
Specimens:
metallographic
specimens
of
the
two
any
30-day
examination
of
of
welded
these
test
stress-corrosion
2219
groups
period
of the
of
and
specimens
alloy
show
specimens
comparison
that
took
of
no stressplace.
None
the
residual
and two unstressed
control
72
ESA STR-212
(May 1984)
specimens from each set which were tensile
tested
after thirty
days'
exposure does not generally indicate any greater loss of strength for the
stress-corrosion
For the
specimens than for the unstressed
Type A specimens
(single
pass
weld)
controls.
one of the
two stress-
corrosion specimens showed a tensile
strength slightly
below that of the
two unstressed
control specimens after thirty
days, but the difference
(232 N/mm2 compared with 250 and 270 N/mm2) is not significant.
For the
Type B specimens (two pass welds) there was no significant
difference
whatever between the tensile
strengths
specimens and the two unstressed
controls
of the two stress-corrosion
tested after thirty
days. The
stress-corrosion
specimens of the Type C set (repair welded) gave tensile
strengths
of 230 and 240 N/mm2 compared with 245 and 249 N/mm2 for the
unstressed
difference.
controls;
this
is again unlikely
The tensile
strength
of the type
to
J
be a significant
(EB welded) stress-
corrosion
specimens after
thirty
days was higher than that of the
corresponding
unstressed
controls
a result
which reflects
the
variability
of tensile
test results
on welded specimens, but certainly
does not indicate
that
any stress-corrosion
cracking
occurred.
All the welded specimens that were tensile
tested failed in the weld bead
itself.
This is to be expected if no stress-corrosion
cracking has taken
place, since it will be the weakest part of the weldment. The weldment
will in general comprise a central as-cast unheat-treated
weld bead, next
to which wi 11 be a zone of parent metal which has been re-solution
treated
by the heat of the welding and will subsequently
naturally
but will not reach the strength
of the original
artificially
age
aged
material.
Beyond the re-solution
treated zone there will be a zone where
the welding temperature
has produced overageing of the parent metal but
has not been sufficient
to produce re-solution
treatment.
Beyond the band
of over aged material will be the unaffected
parent metal. Of these four
zones the weld bead itself
will have the lowest mechanical strength,
but
the greatest
susceptibility
to stress-corrosion
cracking is usually found
within the heat-affected
zone usually in the re-solution
treated material
next to the weld bead itself.
Consequently,
if there
had been any
significant
stress-corrosion
cracking
in the specimens tensile
tested
after thirty days' exposure, they would have been likely to fail in the
heat-affected
zone
rather
than
in
the
weld
bead.
The variation
in
-
microstructure
weld
for
by transmission
Because
the
have
little
which
the
which
i.e.,
weld
are
give
the
however,
loads
of
Alcoa
Aluminium
N/mm2).
welded
pass
proof
welded
typical
at
proof
stress,
equivalent
N/mm2,
and the
values
the
for
calculated
heat
treated
part,
specimens
a gauge
parent
in.
tensile
weakest
welded
on
entirely
the
important
length
metal,
whereas
short
length
the
stress-corrosion
to
shown
of
make
it
in
these
the
parent
alloy
proof
the
out
tests
for
tested
The Type
to
According
to
the
to
Type J electron
35.6%
of
on the
Type
the
beam welded
parent
0.2%
being
e repair
freedom
refer
UTS
parent
the
not
a typical
N/mm2
to
the
does
PS of
50
66 ksi
A single
which
is
metal.
The Type
at 112 N/mm2 equivalent
stress.
equivalent
the
that
metal.
see tests
115
tests
clear
gives
was
quoted
39.4% of the typical
Short transverse
stress
are
of
carried
were
metal
proof
almost
at which
specimens
to
of
to 345 N/mm2, the typical
value
123
strengths
2219-T851
stress
parent
tested
was
of
tensile
stress
Handbook,
specimens
typical
is
proof
The stress
II.
the
fully
crack ing
is equivalent
in Appendix
weldments,
of
was evaluated
bead.
it
the
plate
the
they
results
ion
75% of
which
(455
of
weld
stress-corros
the
since
and parent
as summarised
of
occurs
by the
zones
Measurements
meaning
interpreting
from
9.4.2
they
yielding
des i gners,
ksi
nature
principally
actual
In
composite
real
represented
the
microscopy,
bead.
consists
the
of
electron
of
strength
each
73
T851
33% of
to 32.5%
weld
typical
specimens
pass
specimens
parent
the
B two
of the
were
metal
at 136 N/mm2,
metal proof stress.
BS L93 Specimens:
There is no doubt about the susceptibility
of this material to stresscorrosion cracking when tested at 75% of the 0.2% proof stress since all
three of the type ST specimens tested at that stress level failed in less
than thirty
days; nor is there any doubt that the material
was not
susceptible
when tested at 15% of the proof stress.
In those tests the
loss of strength shown by the two unstressed control specimens which were
subsequently
tensile
tested
was greater
than that of the two stresscorrosion specimens.
74
ESA STR-212
On1y two unstressed
control
spec imens were exposed
with
(May 1984)
the
three
SCC
specimens tested
at 25% of the proof stress.
Consequently
only one
unstressed
control
specimen was tensile
tested
after
thirty
days'
exposure.
This gave a residual
strength
of 251 N/mm2 compared with
327 N/mm2for the stress-corrosion
specimens. Since the tensile
strength
.
of the specimens tested
the stressed
strength,
associated
in the as-received
and unstressed
due in both
intergranu1ar
cases
attack.
SCC specimens tested
at
presence of intergranu1ar
plate
mater i a1 tested
stress-corrosion
short transverse
In comparing
this
specimens
condition
showed a considerable
in
therefore,
showed, however, the
in all three. The L93
be regarded
as suscept i b 1e to
cracking when loaded to 25% of the proof
direction.
conclusion
reduction
principally
to pitting
corrosion
and
The metallographic
examination
of the
25% of the proof stress
stress-corrosion
cracks
must,
was 374 N/mm2,both
with other
published
stress
stress-corrosion
in the
test
results
for L93 material,
it must be remembered that the degree of
stress-corrosion
susceptibility
shown by this material
in the short
transverse
direction
depends on the rolling procedure used to produce the
plate and on the heat treatment.
Sl i ght 1y under aged materi a 1 shows the
greatest
suscept i bi1 ity,
whi1 e s 1i ght 1y over aged mater i a1 is 1ess
susceptible
9.5
than material
aged to maximum strength.
Conclusions
All 2219-T851 We1dments :
The mechanical-property
results
and photomicrograph results
from all
sets of specimens prove that
no stress-corrosion
cracking
has
initiated
during the 30-day test period. These results
direct these
we1dments into Table I of the ESA PSS-01-736 specification
(i .e.
having a high resistance
.
to stress
corrosion).
The BS L93 P1ate:
Stress-corrosion-cracking
metallography,
existed
75% and 25% of the
failures,
for both sets
0.2% proof
stress
observed
by testing
and
of samples that were tested at
for
this
alloy.
The BS L93
plate
must, therefore,
corrosion
all
cracking.
ESA PSS-01-736 (i.e.
is graded
75
T851
be regarded
This material
forms and tempers,
-
as
susceptible
is equivalent
III
- SUMMARY
OF STRESS-CORROSION
Material is Al 2219 in T851 condition
Test direction
is short transverse
Form of material:
(Type of corrosion test sample)
Mechanical test
results,
0.2%
proof stress
N/mm2
Rolled sheet
(C-rings)
35 mm thick
80 mm thick
105 mm thick
4 meter diameter
forged rings:
( tens i1 e bars)
Weldments, 7 mm plate
(tensile
bars)
TIG (single pass)
TIG (double pass)
TIG (repaired)
5mm plate,
EB (single pass)
alloy
to stress
A summary of the worst-case
stress-corrosion
from this work is given in Table XIII.
TABLE XIII
stress-
to AA 2024 which,
as a Table
having a low resistance
to
test
according
in
to
corrosion).
results
derived
TEST MINIMUM RESULTS
Applied stress
during
corrosion
test
N/mm2
Corrosion
test 3.5%
NaCl a.a.
duration
minimum
(days)
SCC
362
348
374
272
261
281
69
86
86
none
none
none
262
196
39
none
153
149
164
181
115
112
123
136
30
30
30
30
none
none
none
none
-----For comparison BS L 93 90 mmplate
(equivalent
to AA 2024) 15% P.S.
(tensile
bars)
25% P.S.
75% P.S.
332
50
83
249
30
30
21
none
failed
fail ed
76
ESA STR-212
(May 1984)
ACKNOWLEDGEMENT
This
work was supported
Assurance Division,
by the Spacelab Programme and the Product
ESTEC. Acknowledgement is given to Messrs D. Shaw and
H.S. Campbell at the BNF Metals User's
the
stress-corrosion
testing
on the
Consultancy
welded
Service
specimens
who performed
and provided
the
results
that have been compi led into Chapter 9. Thanks are also due to
Messrs M. Froggatt,
D.S. Collins and P.F. Fletcher for their assistance
with the materials
tests.
-
APPENDIX
Tables
and Graphs
for
2219
77
T851
as reproduced
I
from
the
published
literature.
78
TABLE 3.1.2.3.1.
Comparison of the Resistance to Stress Co"osion
of Various Aluminum
Alloys
and Products
Estimate of Highest Sustained Tension Stress (ksi)C at Which Test
Specimens of Different Orientations to the Grain Structure Would
Not Fail in the 3'/2 % NaCl Alternate Immersion Test in 84 Daysf
Alloy and
Temper
Test
Direction
2014 - T6
2219
- T8
2024
- n,
2024
7075
T4
-T8
- T6
Rolled Rod
and Bar
Plate
45
L
LT
ST
45
30
83
L
LT
ST
40C
38c
38c
L
LT
ST
35
20
83
30
L
LT
ST
50C
50C
30
47c
L
LT
ST
50
45
83
50
Extruded Shapes
Section Thickness, Inch
0.25 - I
> 1-2
50
27
45
22
83
30
25
83
35c
35c
35c
35c
35c
38c
38c
38c
50C
37
50C
18
83
60C
50
60C
50
45c
43c
43
15
60
50
60
32
83
35
25
83
54
48
46c
53c
48c
46c,d
50C
48c
43c,d
50C
30
83
15b
lOb
43b
15b
7075
- T76
L
LT
ST
49c
49c
25
7075
- T73
L
LT
ST
50C
48c
43c,d
7079 -T6
L
LT
ST
55c
40
83
60
50
60C
35
83
- T6
L
LT
ST
55
38
83
65
45
65
25
83
L
LT
ST
52c
52c
25
55c
52c
25
7178
7178 -T76
52c
49c
25
50
48
43c.d
3Lowest stress at which tests were conducted;
failures were obtained.
bRatings are for transverse specimens machined from round or square bar stock.
CHighest stress at which tests were conducted;
on failure observed.
dThese values will be lower for sections greater than 3" thick, but will be at least 75% ofthe
eSee Section 9.5.2 for test method used to determine
fTests performed at Alcoa Reasearch Laboratories.
Ref:
Hand
Forgings
guaranteed
yield strength.
values.
Mil-Handbook 5c, 15 September 1976, page 3-19.
-
T851
79
Table 2: Stress corrosion resistance of some
2000 and .7000 series aluminium alloys
in 3.5% NaCl with .stresses
in the short
42
43
)
)
transverse d Jrec t Ion
o
Alloy-temper
des ignation
Kr
M~f~312
Smooth specimen
threshold stress
MN/m2
9
48
<55
300
275
2219-T37
2219-T62
2219-T87
< 9
,..,28
< 69
>220
>280
2014-T451
2014-T651
< 9
< 8
55
7075-T651
7075-T7651
7075-T7351
8
<22
--23
48
170
>300
7178-T651
7178-T7651
8
,..,19
48
170
7050-T7651X
7050-T73651
,..,10
25
2024-T351
2024-T4
2024-T62
2024-T851
7475-T7351
>300
Ref: WANHILL, R.J. and VAN GESTEL, G.F., "Aluminium Alloys in the
Aircraft
Industries".
Synlposium organised
by the Associazione
Italiana
Metallurgica
and the Instituto
Sperimentale
dei
Metalli
Leggeri,
Turin,
1-2 October
1976,
pages
9-19.
ESA STR-212
80
(May 1984)
Table III. Estimate of The Highest Sustained Tension Stress at Which Test
Specimens of Different Orientations to The Grain Structure Would Not Fail
by SCC in The 3,5 Pct NaCI Alternate Immersion Test (84 Days) or in Inland
Industrial Atmosphere (1 Year), Whichever is Lower
Alloy
and
Tcmper
Direction
of Applied
51ress
~014-T6
~~19-n7
~0~4-T3.T4
~0~4-T8
7039-T64
707S-T6
7075-T76
707S-T73
71 78-T6
7 178-T76
7079-T6
7049.T73
70S0.T736
717S-T736
RX 720
RR 58
DTD 3067
DTD 3066
AZ 74
Ref:
SPEIDEL,
L
LT
5T
L
LT
5T
L
LT
5T
L
LT
5T
L
LT
5T
L
LT
5T
L
LT
5T
L
LT
5T
L
LT
5T
L
LT
5T
L
LT
5T
5T
5T
5T
5T
L
5T
5T
5T
5T
Plates
Extrusions
Forgings
MNfm2
(ksi)
MNfm2
(ksi)
MNfm2
(ksi)
310
210
<55
>270
>260
>260
170
140
<55
>340
>340
200
>290
240
<35
340
310
<55
>340
>340
170
>340
>330
>300
380
260
<55
>360
>360
170
>380
270
<55
(45)
(30)
«8)
(>40)
(>38)
(>38)
(25)
(20)
«8)
(>50)
(>50)
(30)
(>42)
(35)
«5)
(SO)
(445)
«8)
(>49)
(>49)
(25)
(>50)
(>48)
(>43)
(55)
(38)
«8)
(>52)
(>52)
(25)
(>55)
(40)
«8)
310
ISO
<55
>240
>240
>240
>340
120
<55
>410
>340
>310
(45)
(22)
«8)
(>35)
()8S)
(>35)
(>50)
(18)
«8)
(>60)
(>50)
(>45)
210
170
<55
>260
>260
>260
(30)
(25)
«8)
(>38)
(>38)
(>38)
290
290
100
(43)
(43)
(IS)
410
220
<55
>360
>340
170
>360
>330
>300
450
170
<55
>380
>360
170
>410
240
<55
(60)
(32)
«8)
(>52)
(>49)
(25)
(>53)
(>48)
(>43)
(65)
(25)
«8)
(>55)
(>52)
(25)
(>60)
(35)
«8)
240
170
<55
(35)
(25)
«8)
>170
>300
>270
140
140
(>25)
(>44)
(>40)
(20)
(20)
>340
>330
>300
(>50)
(>48 )
(>43)
>340
210
<55
""170
>170?
""170
(>50)
(30)
«8)
(""25)
(>2S?)
(""25)
310
(45)
H.D., "Stress Corrosion Cracking of Aluminium Alloys",
Met. Trans.,
6A, 1975, pages 631-651.
st ress
intensity.
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21-Summary of stress
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Ref:
corrosion crack growth rates in
alloys based on the aluminum-copper
system.
SPEIDEL, r.1.0., "Stress Corrosion Cracking of Aluminium Alloys",
Met. Trans., 6A, 1975, pages 631-651.
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87
T851
APPENDIX
Classification
II
of tempers
I
IFORM
of Al 2219
CONDITIONS AVAILABLE
I
ISheet
or plate
0, T31,
IWire,
rod
T 851
IExtruded
and bar
rod,
0, T31,
tubes
T8510,
I Bar and shapes
IRolled ring
I
- 0
- F
- T31
- T351
- T37
- T62
- T8l
- T851
T6,
Annealed
As fabricated
Solution
heat
straightening.
Solution
T351,
T62,
T3511,
T62,
T851,
T87
T81
T8511
cold
stress
worked
relieved
by
flattening
by stretching
or
to produce
a permanent set of 1 to 3% (no straightening
after stretching).
So1ut i on heat treated
and co 1d worked by reduct i on of approx.
8%..
Solution heat treated and artificially
aged by the user.
-T 31 precipitation
heat treated
in a manner to obtain certain*
good mechanical properties.
Solution heat treated,
stress relieved by stretching
to produce
a permanent set of 1 to 3%, and artificially
receive no straightening
after stretching.
- T87
T81,
T851
treated,
heat treated,
T3510,
T37,
-T 37 precipitation
good
mechanical
stress-corrosion
*See Mil Spec.-A-8920A,
aged. Plate
shall
heat treated
in a manner to obtain certain*
properties
and to be capable
of meeting
requirements.
20 May 1963, Table II.
88
ESA STR-212
(BLANK PAGE)
(May 1984)
-
89
T851
APPENDIX
TRANSMISSION
1. One
TIG
ELECTRON MICROSCOPY OF Al 2219-T-851
welded
electron
plate
microscopy
hoped
the
plate,
heat-affected
having
similar
extent
(HAZ)
acceleration
voltage
of
and polished
9.
A Siemens
100
kV and the
from
age hardening
of
appropriate
aluminium
to
hardness
testing.
metal
to
of
those
of
regions
2219,
a welded
plate
specimen
used
five
type
with
consisted
of the
was
parent
was
specimens
It
in the
the
microscope
alloy
transmission
hardening
weld
etc.
WELD SAMPLE
submitted
and
and
temper
Chapter
been
of precipitation
composition,
in
has
examination
zone
A described
In the
sample
(TEM)
to determine
machined
I II
of
weld
an
foils
sample.
structures
can
be
recognised:-
- Supersaturated
- G.P.
solid
solution
1 zones,
- G.P. 2 zones,
also
called
~",
- QI and
- Q or CuAh.
These
structures
-as
in other
they
are
solid
ageing
success
solution
structures.
the
generally
tend
probably
on the
and are
eventually
time
slowly
i ve
steps
to
CuA12
and
to
of
of
or
temperatures
and precipitate
replaced
in
is
1 zones
as the
in
the
order
of
intermetallic
of
whether
competing
material
and other
but
supersaturated
nucleated,
bulk
matrix.
sequence,
as to
i on from
on dislocations
of
i oned
disagreement
transformat
by platelets
the
above-ment
independently
G.P.
planes
the
there
the
be nucleated
(100)
in
-
processes
Formation
zones
form
is
rapid
defects,
and
most
G.P.
1 zones
grow
in size
G.P.
2 zones.
With
ageing
150 DC,
the
compound
G.P.
2 zones
CuA12.
grow
90
(May 1984)
ESA STR-212
2.
Parent
Plate
(Fig.
Al).
From the morphology of the precipitates
patterns,
they were identified
as
(G. P. 2 zones).
Thi s is cons i stent
according
to the T851 specification
intermetallic
particles
and their electron diffraction
predominantly
Q' with some Q"
with the plate heat treatment
(18 hours
were observed
in this
at 17PC).
field
No residual
of view.
3. Weld Metal
There was no evidence of ~I or CuA12 in the structure
metal. This is also consistent
with no post-weld ageing).
4. Heat-affected
lone (Figures
Examination of the foils
more
evidence
boundaries.
preparation
of
with the weld temper
of the weld
(i.e.
chill
cast
A3, A4 and A5)
from the HAl show less ~I precipitation
CuA12 precipitation,
particularly
at
and
the
grain
Many of the large precipitates
were lost during sample
- they are more noble than the matrix and cause rapid
dissolution
of their surrounding support
in Figures
A3 - A5 are considered
progressively
more overaged.
material.
The structures
to show regions
that
seen
are
A region
adjacent
of re-solution
treated
material
in the HAl immediately
to the weld pool
and caused by the high welding
temperature - was not found in this TEMexamination.
5. Conclusions
The hardness variations
across the welded plates
show a change from
approx i mate 1y 140 DPN in the parent plate to 90 DPN in the we1d. These
values
reflect
- The
the microstructure
parent plate material
and ~I precipitates.
-
of the alloy:
is strengthened
The HAl shows ~I and CuA12 precipitates,
of slight overageing and hence softening
by the presence
of ~" (GP 2)
the latter
providing
within the HAl.
evidence
- The weld
metal is single phase: no precipitates
were found.
Strengthening
of the weld metal can be produced by artificially
the weld. This would, however, probably produce some softening
parent plate and HAl.
ageing
of the
Figure Al
-
Transmission
electron
-
91
T851
micrograph
of parent
Figure A2 - T.E.M. of weld metal at x 70,000.
plate
at x 80,000.
ESA STR-212
92
,
r--
-
~,
t
----
Figure A3 - T.E.M. of HAZ at x120,OOO.
,
I..
Figure A4
- T.E.M.
of HAZ at x40,OOO.
--
"'
(May 1984)
CORROSION PROPERTIES OF Al 2219 - T851
..
Figure
A5 - T.E.r~.
of HAZ at x160,OOO.
93
ESA STR-212
94
(BLANK PAGE)
(May 1984)

The corrosion properties of Spacelab structural alloy - ESMAT

Transcription

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