U.S. patent application number 10/725501 was filed with the patent office on 2004-06-10 for exfoliation resistant aluminium-magnesium alloy.
Invention is credited to Haszler, Alfred Johann Peter, Sampath, Desikan.
Application Number | 20040109787 10/725501 |
Document ID | / |
Family ID | 8240175 |
Filed Date | 2004-06-10 |
United States Patent
Application |
20040109787 |
Kind Code |
A1 |
Haszler, Alfred Johann Peter ;
et al. |
June 10, 2004 |
Exfoliation resistant aluminium-magnesium alloy
Abstract
Aluminium-magnesium alloy product for welded mechanical
construction, having the following composition, in weight percent:-
1 Mg 3.5-6.0 Mn 0.4-1.2 Zn 0.4-1.5 Zr 0.25 max. Cr 0.3 max. Ti 0.2
max. Fe 0.5 max. Si 0.5 max. Cu 0.4 max. one or more selected from
the group: 2 Bi 0.005-0.1 Pb 0.005-0.1 Sn 0.01-0.1 Ag 0.01-0.5 Sc
0.01-0.5 Li 0.01-0.5 V 0.01-0.3 Ce 0.01-0.3 Y 0.01-0.3 Ni 0.01-0.3
others (each) 0.05 max. (total) 0.15 max. balance aluminum.
Inventors: |
Haszler, Alfred Johann Peter;
(Vallendar, DE) ; Sampath, Desikan; (Koblenz,
DE) |
Correspondence
Address: |
STEVENS, DAVIS, MILLER & MOSHER, LLP
Suite 850
1615 L. Street N.W.
Washington
DC
20036
US
|
Family ID: |
8240175 |
Appl. No.: |
10/725501 |
Filed: |
December 3, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10725501 |
Dec 3, 2003 |
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09959602 |
Feb 15, 2002 |
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6695935 |
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09959602 |
Feb 15, 2002 |
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PCT/EP00/04410 |
May 4, 1999 |
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Current U.S.
Class: |
420/542 |
Current CPC
Class: |
C22C 21/06 20130101 |
Class at
Publication: |
420/542 |
International
Class: |
C22C 021/06 |
Foreign Application Data
Date |
Code |
Application Number |
May 4, 1999 |
EP |
99201391.2 |
Claims
1. Aluminium-magnesium alloy product for welded mechanical
construction, having the following composition, in weight
percent:-
12 Mg 3.5-6.0 Mn 0.4-1.2 Zn 0.4-1.5 Zr 0.25 max. Cr 0.3 max. Ti 0.2
max. Fe 0.5 max. Si 0.5 max. Cu 0.4 max.
one or more selected from the group:
13 Bi 0.005-0.1 Pb 0.005-0.1 Sn 0.01-0.1 Ag 0.01-0.5 Sc 0.01-0.5 Li
0.01-0.5 V 0.01-0.3 Ce 0.01-0.3 Y 0.01-0.3 Ni 0.01-0.3
others (each) 0.05 max. (total) 0.15 max. balance aluminium.
2. Aluminium-magnesium alloy product according to claim 1, wherein
the Bi content is in the range of 0.01 to 0.1 wt. %, and preferably
0.01 to 0.05 wt. %.
3. Aluminium-magnesium alloy product according to claim 1 or 2,
wherein the Li content is in the range of 0.1 to 0.3 wt. %.
4. Aluminium-magnesium alloy product according to any one of claims
1 to 3, wherein the Mg content is in the range of 4.0 to 5.6 wt.
%
5. Aluminium-magnesium alloy product according to claim 4, wherein
the Mg content is in the range of 4.6 to 5.6 wt. %.
6. Aluminium-magnesium alloy product according to any one of claims
1 to 5, wherein the Zn content is in the range of 0.4 to 0.9 wt.
%.
7. Aluminium-magnesium alloy product according to any one of claims
1 to 6, wherein the Zr content is in the range of 0.05 to 0.25 wt.
%.
8. Aluminium-magnesium alloy product according to any one of claims
1 to 7, wherein the product is provided in the form of a rolled
product, an extruded product or a drawn product.
9. Aluminium-magnesium alloy product according to any one of claims
1 to 8 having a temper selected from a soft temper and a
work-hardened temper.
10. Welded structure comprising at least one welded plate or
extrusion made of aluminium-magnesium alloy product according to
any one of claims 1 to 9.
11. Welded structure according to claim 10, wherein the proof
strength of the weld of said plate or extrusion is at least 140
MPa.
12. Welded structure according to claim 10, having an improved
resistance to exfoliation resistance when sensitised for at least
10 days at 120.degree. C.
13. Welded structure according to claim 10, having an exfoliation
resistance of PA or better in an ASSET test in accordance with ASTM
G66 and when sensitised in a soft temper for 20 days at 120.degree.
C.
14. Welded structure according to claim 10, having an exfoliation
resistance of PA or better in an ASSET test in accordance with ASTM
G66 and when sensitised in a work hardened temper for 16 days at
100.degree. C.
15. Welded structure according to any one of claims 10 to 14,
wherein the welded structure is a marine vessel.
16. Welded structure according to any one of claims 10 to 14,
wherein the welded structure is a container for land
transportation.
17. Use of an aluminium-magnesium alloy product according to any
one of claims 1 to 16 at an operating temperature greater than
80.degree. C.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an aluminium-magnesium
alloy with a magnesium content in the range of 3.5 to 6 wt. % in
the form of rolled products and extrusions, which are particularly
suitable to be used in the form of sheets, plates or extrusions in
the construction of welded or joined structures, such as storage
containers and vessels for marine and land transportation.
Extrusions of the alloy of the invention can be used as stiffeners
in engineering constructions. Further the invention relates to a
method of manufacturing the alloy of the invention.
DESCRIPTION OF THE PRIOR ART
[0002] For this invention reference is being made to aluminium
wrought series alloys having a designation number in accordance
with the Aluminium Association as published in February 1997 under
"International Alloy Designations and Chemical Composition Limits
for Wrought Aluminum and Wrought Aluminum Alloys".
[0003] In aluminium-magnesium alloys, theoretically, at room
temperature up to about 1.8 wt. % Mg can be retained in solid
solution. However, under practical conditions, up to about 3.0 wt.
% Mg can be retained in solid solution. As a consequence, in
aluminium-magnesium alloys containing more than 3.5 wt. %
magnesium, the magnesium in solid solution is unstable and this
unstable solid solution leads to grain boundary, anodic
precipitations of Al.sub.8Mg.sub.5 intermetallics which in turn
renders the material to be susceptible to corrosion attack. Mainly
due to this reason, AA5454-series material in the soft temper
(O-temper) are used in the construction of vessels which are
expected to serve at temperatures above 65.degree. C. In case of
service temperatures below 65.degree. C., AA5083-series material in
the soft temper are commonly used. Material of the AA5083-series is
significantly stronger than AA5454-series. Although stronger, the
inferior corrosion resistance of the AA5083-series material limits
its use to those applications where long term corrosion resistance
at above ambient temperatures is not required. Because of the
corrosion related problems, in general AA5xxx-series material
having magnesium levels of only up to 3.0 wt. % are currently
accepted for use in those applications which require service at
temperatures above 80.degree. C. This limitation on the magnesium
level in turn limits the strength that can be achieved after
welding and consequently on the allowed material thickness that can
be used in the construction of structures such as tanker
lorries.
[0004] Some disclosures of Al--Mg alloys found in the prior art
literature will be mentioned below.
[0005] U.S. Pat. No. 4,238,233 discloses an aluminium alloy for
cladding excellent in sacrificial anode property and
erosion-corrosion resistance, which consists essentially of, in
weight percentage:-
[0006] Zn 0.3 to 3.0%
[0007] Mg 0.2 to 4.0%
[0008] Mn 0.3 to 2.0%
[0009] balance aluminium and incidental impurities and further
containing at least one element selected from the group consisting
of:
[0010] In 0.005 to 0.2%
[0011] Sn 0.01 to 0.3
[0012] Bi 0.01 to 0.3%
[0013] provided that the total content of In, Sn and Bi being up to
0.3%.
[0014] This disclosure does not relate to the field of welded
mechanical construction.
[0015] JP-A-05331587 discloses an aluminium alloy having a chemical
composition of Mg 2.0 to 5.5% and 1 to 300 ppm, in total, of one or
more elements selected from the group consisting of Pb, In, Sn, Ga
and Ti, balance aluminium and impurities. Optionally further
element like Cu, Zn, Mn, Cr, Zr, Ti may be added as alloying
elements. The minor addition of Pb, In, Sn Ga, and Ti is to improve
the adhesion of a plating film. Also, this disclosure does not
relate to the field of welded mechanical construction.
[0016] FR-A-2,329,758 discloses an aluminium-magnesium alloy having
Mg in the range of 2 to 8.5% and further having Cr in a range of
0.4 to 1.0% as a mandatory alloying element. This disclosure does
not relate to the field of welded mechanical construction.
[0017] U.S. Pat. No. 5,624,632 discloses an substantially zinc-free
and lithium-free aluminium alloy product for use as a damage
tolerant product for aerospace applications.
SUMMARY OF THE INVENTION
[0018] An object of the present invention is to provide an
aluminium-magnesium alloy in the form of a rolled product or an
extruded product or a drawn product, combined with substantially
improved long term corrosion resistance after welding as compared
to those of the standard AA5454 alloy and having improved strength
as compared to those of the standard AA5083 alloy.
[0019] A further object of present invention is to provide an
aluminium-magnesium alloy in the form of a rolled product or an
extruded product or a drawn product, combined with substantially
improved exfoliation resistance after welding as compared to those
of the standard AA5083 alloy.
[0020] Another object of present invention is to provide an
aluminium-magnesium alloy in the form of a rolled product or an
extruded product or a drawn product, combined with substantially
improved exfoliation resistance after welding in a sensitised
condition as compared to those of the standard AA5083 alloy.
[0021] According to the invention there is provided an
aluminium-magnesium alloy product, preferably in the form of a
rolled product or an extruded product or a drawn product, for
welded mechanical construction, having the following composition,
in weight percent:-
3 Mg 3.5-6.0 Mn 0.4-1.2 Zn 0.4-1.5 Zr 0.25 max. Cr 0.3 max. Ti 0.2
max. Fe 0.5 max. Si 0.5 max. Cu 0.4 max.
[0022] one or more selected from the group:
4 Bi 0.005-0.1 Pb 0.005-0.1 Sn 0.01-0.1 Ag 0.01-0.5 Sc 0.01-0.5 Li
0.01-0.5 V 0.01-0.3 Ce 0.01-0.3 Y 0.01-0.3 Ni 0.01-0.3
[0023] others (each) 0.05 max.
[0024] (total) 0.15 max.
[0025] balance aluminium.
[0026] By the invention we can provide aluminium-magnesium alloy
products in the form of a rolled product or an extrusion, with
substantially improved long term corrosion resistance in both soft
temper (O-temper) and work- or strain-hardened temper (H-tempers)
as compared to those of the standard AA5454 alloy and having
improved strength as compared to those of the standard AA5083 alloy
in the same temper. Further, alloy products of the present
invention have also been found with improved long term exfoliation
corrosion resistance at temperatures above 80.degree. C., which is
the maximum temperature of use for the AA5083 alloy. Further, the
alloy products in accordance with the invention have been found to
have an improved exfoliation corrosion resistance, in particular
when brought in an sensitised condition.
[0027] The invention also consists in a welded structure having at
least one welded plate or extrusion of the alloy set out above.
Preferably the proof strength of the weld is at least 140 MPa.
[0028] The invention also consists in the use of the aluminium
alloy of the invention as weld filler wire, and is preferably
provided in the form of drawn wire.
[0029] It is believed that the surprisingly improved properties
available with the invention are achieved by a careful selection of
the combination of alloying elements. Particularly higher strength
levels in both strain- or work-hardened (H-tempers) and soft
tempers (O-tempers) are achieved by increasing the levels of Mg, Mn
and adding Zr, and the long term corrosion resistance at higher Mg
levels is achieved by precipitating anodic Mg and/or Zn containing
intermetallics within the grains. In accordance with the invention
it has been found that the grain interior precipitation can be
further promoted by deliberate addition of one or more of the
following elements selected from the group consisting of: Bi 0.005
to 0.1, Pb 0.005 to 0.1, Sn 0.01 to 0.1, Ag 0.01 to 0.5, Sc 0.01 to
0.5, Li 0.01 to 0.5, V 0.01 to 0.3, Ce 0.01 to 0.3, Y 0.01 to 0.3,
and Ni 0.01 to 0.3.
[0030] The precipitation of Mg and/or Zn containing intermetallics
within grains effectively reduces the volume fraction of grain
boundary precipitated and highly anodic, binary AlMg intermetallics
and thereby providing significant improvement in the corrosion
resistance to the aluminium alloys at higher Mg levels employed.
And furthermore, the deliberate additions of the indicated elements
in the indicated ranges not only enhances grain body precipitation
of anodic intermetallics but also, either discourage grain boundary
precipitation, or disrupt continuity of anodic intermetallics that
can otherwise be formed.
[0031] The reasons for the limitations of the alloying elements are
described below. All composition percentages are by weight.
[0032] Mg: Mg is the primary strengthening element in the alloy. Mg
levels below 3.5% do not provide the required weld strength and
when the addition exceeds 6.0%, severe cracking occurs during hot
rolling. The preferred Mg level is in the range of 4.0 to 5.6%, and
a more preferred range is 4.6 to 5.6%.
[0033] Mn: Mn is an essential additive element. In combination with
Mg, Mn provides the strength to both the rolled product and the
welded joints of the alloy. Mn levels below 0.4% cannot provide
sufficient strength to the welded joints of the alloy. Above 1.2%
the hot rolling becomes very difficult. The preferred range for Mn
is 0.4 to 0.9%, and more preferably in the range of 0.6 to 0.9%,
which represents a compromise between strength and ease of
fabrication.
[0034] Zn: Zn is an important additive for corrosion resistance of
the alloy. Further zinc also contributes to some extent to the
strength of the alloy in the work-hardened tempers. Below 0.4%, the
Zn addition does not provide as much intergranular corrosion
resistance equivalent to those AA5083 at Mg levels larger than
5.0%. At Zn levels above 1.5%, casting and subsequent hot rolling
becomes difficult, especially on an industrial scale of
manufacturing. A more preferred maximum for the Zn level is 0.9%. A
very suitable range for the Zn is 0.5 to 0.9%, as a compromise in
mechanical properties both before and after welding and corrosion
resistance after welding.
[0035] Zr: Zr is important for achieving a fine grain refined
structure in the fusion zone of welded joints using the alloy of
the invention. Zr levels above 0.25% tend to result in very coarse
needle-shaped primary particles which decrease ease of fabrication
of the alloys and formability of the alloy rolled products or
extrusions. The preferred minimum of Zr is 0.05%, and to provide
sufficient grain refinement a preferred Zr range of 0.10 to 0.20%
is employed.
[0036] Cr: Cr improves the corrosion resistance of the alloy.
However, Cr limits the solubility of Mn and Zr. Therefore, to avoid
formation of coarse primaries, the Cr level must not be more than
0.3%. A preferred range for Cr is up to 0.15%.
[0037] Ti: Ti is important as a grain refiner during solidification
of both ingots and welded joints produced using the alloy of the
invention. However, Ti in combination with Zr forms undesirable
coarse primaries. To avoid this, Ti levels must be not more than
0.2% and the preferred range for Ti is not more than 0.1%.
[0038] Fe: Fe forms Al--Fe--Mn compounds during casting, thereby
limiting the beneficial effects due to Mn. Fe levels above 0.5%
causes formation of coarse primary particles which decrease the
fatigue life of the welded joints of the alloy of the invention.
The preferred range for Fe is 0.15 to 0.35%, and more preferably
0.20 to 0.30%.
[0039] Si: Si forms Mg.sub.2Si which is practically insoluble in
aluminium-magnesium alloys containing more than 4.4% magnesium.
Therefore, Si limits the beneficial effects of Mg. Further, Si also
combines with Fe to form coarse AlFeSi phase particles which can
affect the fatigue life of the welded joints of the alloy rolled
product or extrusion. To avoid the loss in Mg as primary
strengthening element, the Si level must be kept below 0.5%. The
preferred range for Si is 0.07 to 0.25%, and more preferably 0.10
to 0.20%.
[0040] Cu: Cu should be not more than 0.4%. Cu, since Cu levels
above 0.4% give rise to unacceptable deterioration in pitting
corrosion resistance of the alloy of the invention. The preferred
level for Cu is nor more than 0.1%.
[0041] Bi: In the case of deliberate low level addition, for
example 0.005%, Bi preferentially segregates at grain boundaries.
It is believed that this presence of Bi in the grain boundary
networks discourage the precipitation of Mg containing
intermetallics. At levels above 0.1%, weldability of the aluminium
alloy of the present invention deteriorates to an unacceptable
level. A preferred range for Bi addition is 0.01 to 0.1%, and more
preferably 0.01 to 0.05%. It should be mentioned here that it is
known in the art that small additions of bismuth, typically 20 to
200 ppm, can be added to aluminium-magnesium series wrought alloys
to counteract the detrimental effect of sodium on hot cracking.
[0042] Pb and/or Sn: In case of low levels of addition, for example
0.01%, both Pb and/or Sn preferentially segregates at the grain
boundaries. This presence of Pb and/or Sn in the grain boundary
networks discourage the precipitation of Mg containing
intermetallics. At levels of Pb and/or Sn above 0.1%, weldability
of the alloys of the present invention deteriorates to an
unacceptable level. A preferred minimum level for Pb addition is
0.005%, and for Sn a preferred minimum level is 0.01%. A more
preferred range of Pb is 0.01 to 0.1%, and most preferably 0.03 to
0.1%. A more preferred range of Sn is 0.01 to 0.1%, and most
preferably 0.03 to 0.1%. A preferred range of the combination of Sn
and Pb is 0.01 to 0.1%, and more preferably 0.03 to 0.1%.
[0043] The elements Li, Sc, and Ag, either alone or in combination
at levels above 0.5% forms Mg containing intermetallics which are
present on the grain boundary thus disrupting formation of
continuous binary Mg containing anodic intermetallics during long
term service or during elevated temperature service of the
aluminium alloy of this invention. The threshold level for these
elements to produce interruptions to anodic grain boundary
intermetallics network, depends on other elements in solid
solution. When added, the preferred maximum for Li or/and Sc or/and
Ag is 0.3%. The preferred minimum is 0.01%, and more preferably
0.1%. Above 0.5% Ag and Sc additions become economically
unattractive. It has been found that the presence of Ag, Sc, and Li
alone or in combination are most effective for the higher levels of
Mg in the aluminium alloy, with a preference for Mg levels in the
range of 4.6 to 5.6%.
[0044] The elements V, Ce, Y, and Ni when added individually or in
combination at levels above 0.01% in the alloy of the invention
form intermetallics primarily with aluminium. These intermetallics
promote the precipitation of Mg containing anodic intermetallics in
grain interiors. In addition, when present, they also provide
strength at elevated temperatures to the alloy of the invention.
However, at levels above 0.3% industrial casting becomes more
difficult. A more preferred range for these alloying elements
individually or in combination is in the range of 0.01 to
0.05%.
[0045] The balance is aluminium and inevitable impurities.
Typically each impurity element is present at 0.05% maximum and the
total of impurities is 0.15% maximum.
[0046] In a further aspect of the invention there is provided is a
method for the manufacturing the aluminium alloy as set out above.
The rolled products of the alloy of the invention can be
manufactured by preheating, hot rolling, optionally cold rolling
with or without interannealing, and final annealing/ageing of an
Al--Mg alloy ingot of the selected composition. The reasons for the
limitations of the processing route of the method in accordance
with the invention are described below.
[0047] The preheating prior to hot rolling is usually carried out
at a temperature in the range 300 to 530.degree. C. The optional
homogenisation treatment prior to preheating is usually carried out
at a temperature in the range 350 to 580.degree. C. in single or in
multiple steps. In either case, homogenisation decreases the
segregation of alloying elements in the material as cast. In
multiple steps, Zr, Cr, and Mn can be intentionally precipitated
out to control the microstructure of the hot mill exit material. If
the treatment is carried out below 350.degree. C., the resultant
homogenisation effect is inadequate. If the temperature is above
580.degree. C., eutectic melting might occur resulting in
undesirable pore formation. The preferred time of the
homogenisation treatment is between 1 and 24 hours.
[0048] Using a strictly controlled hot rolling process, it is
possible to eliminate cold rolling and/or annealing steps in the
process route for the plates.
[0049] A total 20 to 90% cold rolling reduction may be applied to
hot rolled plate or sheet prior to final annealing. Cold rolling
reductions such as 90% might require intermediate annealing
treatment to avoid cracking during rolling. Final annealing or
ageing can be carried out in cycles comprising of single or with
multiple steps either case, during heat-up and/or hold and/or
cooling down from the annealing temperature. The heat-up period is
preferably in the range of 2 min to 15 hours. The annealing
temperature is in the range of 80 to 550.degree. C. depending on
the temper. A temperature range of 200 to 480.degree. C. is
preferred to produce the soft tempers. The soak period at the
annealing temperature is preferably in the range of 10 min to 10
hours. If applied, the conditions of intermediate annealing can be
similar to those of the final annealing. Furthermore, the materials
that exit the annealing furnace can be either water quenched or air
cooled. The conditions of the intermediate annealing are similar to
those of the final annealing. Stretching or levelling in the range
of 0.5 to 10% may be applied to the final plate.
EXAMPLES
[0050] The following are non-limitative examples of the
invention.
Example 1
[0051] On a laboratory scale of testing eight alloys have been
cast, see Table 1 in which table (-) means <0.001 wt. %. Alloys
1 and 2 are comparative examples, of which alloy 1 is within the
AA5454 range and alloy 2 within the AA5083 range. Alloys 3 to 8 are
all examples of the alloy in accordance with this invention.
[0052] The cast ingots have been homogenised for 12 hours at
510.degree. C., then hot rolled from 80 mm down to 13 mm. Then cold
rolled from 13 mm to 6 mm thick plates. The cold rolled sheets have
been annealed for 1 hour at 350.degree. C., using a heat-up and
cool down rate of 30.degree. C./h, to produce soft temper
materials. Using the AA5183 filler wire diameter of 1.2 mm,
standard MIG welded panels (1000.times.1000.times.6 mm) were
prepared. From the welded panels samples for tensile and corrosion
test were prepared.
[0053] The tensile properties of the welded panels were determined
using standard tensile tests. Resistance to pitting and exfoliation
corrosion of the panels were assessed using the ASSET test in
accordance with ASTM G66. Table 2 list the results obtained, and
where N, PA and PB stands for no pitting, slight pitting and
moderate pitting respectively. The assessment has been done for the
base material, the heat affected zone (HAZ), and the weld seam. For
the tensile properties "0.2% PS" stands for the 0.2% proof
strength, "UTS" stands for ultimate tensile strength, and "Elong"
stands for elongation at fracture.
[0054] From the results of Table 2 it can be seen that as compared
to the reference alloys 1 and 2, the tensile properties of the
alloy product in accordance with the invention are significantly
higher. Further it can be seen from the ASSET test results the
alloys in accordance with the invention are comparable to alloy,
indicating that a similar corrosion resistance as AA5454 material
is obtained, which may be contributed to the addition of either Bi,
Ag or Li.
5TABLE 1 Chemistries of the cast ingots. Alloying element (in wt.
%) Al Mg Mn Zn Zr Cu Cr Fe Si Ti Bi Ag Li 1 2.70 0.75 0.02 0.01
0.05 0.10 0.30 0.15 0.10 -- -- -- 2 4.50 0.53 0.09 0.01 0.03 0.05
0.15 0.09 0.10 -- -- -- 3 4.85 0.65 0.59 0.10 0.03 0.04 0.15 0.09
0.10 0.07 -- -- 4 5.30 0.84 0.55 0.13 0.04 0.05 0.19 0.11 0.01 0.05
-- -- 5 4.62 0.65 0.52 0.12 0.03 0.03 0.15 0.09 0.10 -- 0.05 -- 6
5.15 0.84 0.55 0.13 0.01 0.05 0.19 0.11 0.01 -- 0.07 -- 7 4.79 0.65
0.61 0.12 0.03 0.05 0.15 0.09 0.10 -- -- 0.30 8 5.26 0.84 0.55 0.13
0.02 0.04 0.19 0.11 0.01 -- -- 0.15
[0055]
6TABLE 2 Experimental results. ASSET test results 0.2% PS UTS
Elong. base weld Alloy [MPa] [MPa] [%] material HAZ seam 1 106 237
14 N/PA N/PA N 2 132 292 17 PB PA/PB N 3 150 325 20.5 N/PA N N 4
174 345 22 N N/PA N 5 152 331 20.7 N N N 6 170 349 31.3 N N/PA N 7
159 327 22.6 N N N 8 173 346 21.9 N/PA N/PA N
Example 2
[0056] On a laboratory scale of testing five aluminium alloys have
been cast. The chemical compositions of these four alloys are
listed in Table 3. Alloy 1 is a reference alloy within the range of
standard AA5083 chemistry, and alloys 2 to 5 are examples of the
aluminium alloy product in accordance with this invention.
[0057] The cast ingots have been processed down to a 1.6 mm gauge
sheet product using the following processing route:-
[0058] two-step pre-heat: 410.degree. C. for 4 hours followed by
510.degree. C. for 10 hours, with a heat-up rate of about
35.degree. C./h;
[0059] hot rolling down to 4.3 mm thick sheets;
[0060] cold rolling to 2.6 mm thick sheets;
[0061] inter-annealing at 480.degree. for 10 min;
[0062] final cold rolling down to 1.6 mm thick sheets;
[0063] annealing to produce their temper:-
[0064] (a) O-temper: 480.degree. C. for 15 min;
[0065] (b) H321-temper: 250.degree. C. for 30 min;
[0066] stretching by 1% for O-temper material and stretching by 2%
for H321-temper material;
[0067] TIG welding using AA5183 filler wire (analogue to Example
1);
[0068] sensitising of the welded panels depending on their
temper:-
[0069] (a) O-temper: 120.degree. C. for 0, 10, 20, and 40 days
[0070] (b) H321-temper: 100.degree. C. for 4, 9, 16, and 25
days
[0071] The tensile properties were tested for the both unwelded
H321- and O-temper sheet materials. Euro-norm tensile specimens
were machined along the rolling (L-) and LT-directions of the
sheets. The tensile properties of the materials were determined
using standard tensile tests. Table 4 lists the tensile test
results for unwelded H321-temper material and Table 5 for the
unwelded O-temper material.
[0072] The corrosion performance of welded materials have been
assessed using ASSET test, performed according to ASTM G66
procedure. Tables 6 and 7 list the results obtained for H321-temper
and O-temper material respectively, and the rates N, PA, PB, and PC
respectively represent no pitting, slight pitting, moderate pitting
and severe pitting degrees. EA and EB indicates slight and moderate
exfoliation rendering. The assessment as been done for the base
material and the heat affected zone (HAZ). In all cases the
assessment for the weld seam was "N".
[0073] It can be seen from Tables 4 and 5, that the alloy products
according to this invention show significantly higher tensile
properties in comparison to the AA5083 alloy material in both the
strain hardened H321- and the soft annealed O-tempers. When
comparing the three different Bi-levels of alloys 2 to 4, no
influence of an increasing Bi-level can be found on the tensile
properties.
[0074] It can be seen from Tables 6 and 7, that the welded alloy
products manufactured from the alloy product in accordance with the
invention, both H-temper material and O-temper material, have an
improved exfoliation corrosion resistance in comparison to the
standard AA5083 alloy material. This effect is demonstrated for
both the addition of Bi and V. This effect is more pronounced with
increasing sensitisation.
7TABLE 3 Chemistries of the cast ingots. Alloying elements (in wt
%) Alloy Mg Mn Zn Zr Fe Si Cu Cr Ti Bi V 1 4.50 0.53 0.02 0.01 0.30
0.15 0.05 0.08 0.010 -- -- 2 5.45 0.81 0.58 0.14 0.08 0.09 0.01
0.01 0.020 0.012 -- 3 5.45 0.83 0.58 0.14 0.09 0.09 0.01 0.01 0.020
0.029 -- 4 5.27 0.79 0.47 0.13 0.13 0.08 0.01 0.01 0.020 0.047 -- 5
5.53 0.80 0.59 0.14 0.08 0.09 0.01 0.01 0.020 -- 0.05
[0075]
8TABLE 4 Tensile properties of the base material in H321 temper.
LT-direction L-direction 0.2% PS UTS Elong. 0.2% PS UTS Elong.
Alloy [MPa] [MPa] [%] [MPa] [MPa] [%] 1 253 335 12.6 269 340 9.4 2
294 403 11.6 315 410 8.8 3 282 400 12.1 308 399 9.0 4 275 394 11.1
309 391 9.6 5 279 399 13.4 317 394 9.8
[0076]
9TABLE 5 Tensile properties of the base material in O-temper.
LT-direction L-direction 0.2% PS UTS Elong. 0.2% PS UTS Elong.
Alloy [MPa] [MPa] [%] [MPa] [MPa] [%] 1 132 294 19.0 145 296 17.8 2
163 339 21.0 180 335 18.1 3 163 342 20.7 181 340 17.8 4 166 345
21.5 171 344 17.3 5 164 336 19.0 166 332 19.7
[0077]
10TABLE 6 Corrosion performance of the alloys in H321-temper.
Sensitisation ASSET test results Alloy 100.degree. C. Base material
vs. HAZ 1 none PB PA 4 days P PA 9 days PB PA 16 days PC/EA PB 25
days PC/EB PC 2 none N/PA N 4 days N/PA N 9 days N/PA N 16 days PA
N/PA 25 days PA N/PA 3 none N/PA N 4 days N/PA N 9 days N/PA N 16
days PA PA 25 days PA/PB PA 4 none N/PA N 4 days N/PA N 9 days PA
N/PA 16 days PA PA 25 days PA/PB PA 5 none N/PA N 4 days N/PA N 9
days PA N/PA 16 days PA/PB PA 25 days PA/PB PA/PB
[0078]
11TABLE 7 Corrosion performance of the alloys in O-temper.
Sensitisation ASSET test results Alloy 120.degree. C. Base material
vs. HAZ 1 none PA/PB PA 10 days PA/PB PA 20 days PA/PB PA 40 days
PC/EA PB/PC 2 none N/PA N 10 days N/PA N 20 days PA N 40 days PA/PB
N/PA 3 none N/PA N 10 days N/PA N 20 days PA N 40 days PB PA 4 none
N/PA N 10 days N/PA N 20 days PA/PB N 40 days PB N/PA 5 none N/PA N
10 days N/PA N 20 days PA N 40 days PA/PB N/PA
[0079] While the invention has been described in conjunction with
the exemplary embodiments described above, many equivalent
modifications and variations will be apparent to those skilled in
the art when given those disclosure. Accordingly, the exemplary
embodiments of the invention set forth above are considered to be
illustrative and not limiting. Various changes to the described
embodiments may be made without departing from the spirit and scope
of the invention.
* * * * *