U.S. patent application number 09/785523 was filed with the patent office on 2001-10-04 for aluminium-magnesium alloy plate or extrusion.
Invention is credited to Haszler, Alfred Johann Peter, Sampath, Desikan.
Application Number | 20010025675 09/785523 |
Document ID | / |
Family ID | 8223857 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010025675 |
Kind Code |
A1 |
Haszler, Alfred Johann Peter ;
et al. |
October 4, 2001 |
Aluminium-magnesium alloy plate or extrusion
Abstract
A high strength Al-Mg alloy in plate or extrusion form having
significantly improved strength in both soft and work-hardened
tempers as compared with AA5083 is provided. The materials have
ductility, pitting, stress and exfoliation corrosion resistances
equivalent to those of the AA5083. The materials have improved long
term stress and exfoliation corrosion resistances at temperatures
above 80.degree. C. The composition is 5-6% Mg, >0.6-1.2% Mn,
0.4-1.5% Zn, 0.05-0.25% Zr, up to 0.3% Cr, up to 0.2% Ti, up to
0.5% each Fe and Si, up to 0.4% each Cu and Ag, remainder Al and
inevitable impurities. Manufacture of plate of this alloy is by
homogenizing an ingot, hot rolling the ingot into plate in the
range 400-530.degree. C., cold rolling the plate with or without
inter-annealing, final and optionally inter-annealing of the cold
rolled material at temperatures in the range 200-550.degree. C.
Inventors: |
Haszler, Alfred Johann Peter;
(Vallendar, DE) ; Sampath, Desikan; (Beverwijk,
NL) |
Correspondence
Address: |
STEVENS, DAVIS, MILLER & MOSHER, LLP
Suite 850
1615 L Street N.W.
Washington
DC
20036
US
|
Family ID: |
8223857 |
Appl. No.: |
09/785523 |
Filed: |
February 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09785523 |
Feb 20, 2001 |
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09155652 |
Feb 24, 1999 |
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6238495 |
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09155652 |
Feb 24, 1999 |
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PCT/EP97/01623 |
Mar 27, 1997 |
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Current U.S.
Class: |
148/440 |
Current CPC
Class: |
C22C 21/06 20130101;
C22C 21/10 20130101 |
Class at
Publication: |
148/440 |
International
Class: |
C22C 021/06; C22C
021/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 4, 1996 |
EP |
96200967.6 |
Claims
1. Aluminium-magnesium alloy in the form of a plate or an
extrusion, having the following composition in weight percent:
11 Mg 5.0-6.0 Mn >0.6-1.2 Zn 0.4-1.5 Zr 0.05-0.25 Cr 0.3 max. Ti
0.2 max. Fe 0.5 max. Si 0.5 max. Cu 0.4 max. Ag 0.4 max. balance Al
and inevitable impurities.
2. Aluminium-magnesium alloy according to claim 1 having a temper
selected from a soft temper and a work-hardened temper.
3. Aluminium-magnesium alloy according to claim 1 or 2 wherein the
Mg content is in the range 5.0-5.6 wt %.
4. Aluminium-magnesium alloy according to any one of claims 1 to 3
wherein the Mn content is at least 0.7 wt %.
5. Aluminium-magnesium alloy according to claim 4 wherein the Mn
content is in the range 0.7-0.9 wt %.
6. Aluminium-magnesium alloy according to any one of claims 1 to 5
wherein the Zn content is not more than 1.4 wt %.
7. Aluminium-magnesium alloy according to claim 6 wherein the Zn
content is not more than 0.9 wt %.
8. Aluminium-magnesium alloy according to any one of claims 1 to 7
wherein the Zr content is in the range 0.10-0.20 wt %.
9. Aluminium-magnesium alloy according to any one of claims 1 to 8
wherein the Mg content is in the range 5.2
10. Aluminium-magnesium alloy according to any one of claims 1 to 9
wherein the Cr content is not more than 0.15 wt %.
11. Aluminium-magnesium alloy according to any one of claims 1 to
10 wherein the Ti content is not more than 0.10 wt %.
12. Aluminium-magnesium alloy according to any one of claims 1 to
11 wherein the Fe content is in the range 0.2-0.3 wt %.
13. Aluminium-magnesium alloy according to any one of claims 1 to
12 wherein the Si content is in the range 0.1-0.2 wt %.
14. Aluminium-magnesium alloy according to any one of claims 1 to
13 wherein the Cu content is not more than 0.1 wt %.
15. Welded structure comprising at least one welded plate or
extrusion made of aluminium-magnesium alloy according to any one of
claims 1 to 14.
16. Welded structure according to claim 15 wherein the proof
strength of the weld of said plate or extrusion is at least 140
MPa.
17. Use of an aluminium-magnesium alloy 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 in the form of plates and extrusions, which is particularly
suitable to be used in the construction of large welded structures
such as storage containers and vessels for marine and land
transportation. For example, the plates of this invention can be
used in the construction of marine transportation vessels such as
catamarans of monohull type, fast ferries, high speed light craft,
and jet rings for the propulsion of such vessels. The alloy plates
of the present invention can also be used in numerous other
applications such as structural materials for LNG tanks, silos,
tanker lorries and as tooling and moulding plates. Plates may have
a thickness in the range of a few mm, e.g. 5 mm, up to 200 mm.
Extrusions of the alloy of this invention can be used for example
as stiffeners and in superstructures of marine vessels such as fast
ferries.
DESCRIPTION OF THE RELATED ART
[0002] Al-Mg alloys with Mg levels >3% are extensively used in
large welded constructions such as storage containers and vessels
for land and marine transportation. A standard alloy of this type
is the AA5083 alloy having the nominal composition, in wt %:
1 Mg 4.0-4.9 Mn 0.4-1.0 Zn .ltoreq.0.25 Cr 0.05-0.25 Ti
.ltoreq.0.15 Fe .ltoreq.0.4 Si .ltoreq.0.4 Cu .ltoreq.0.1 others
(each) .ltoreq. 0.05 (total) .ltoreq. 0.15 balance Al.
[0003] In particular, AA5083 alloy plates in the soft and
work-hardened tempers are used in the construction of marine
vessels such as ships, catamarans and high speed craft. Plates of
the AA5083 alloy in the soft temper are used in the construction of
tanker lorries, dump trucks, etc. The main reason for the
versatility of the AA5083 alloy is that it provides good
combinations of high strength (both at ambient and cryogenic
temperatures), light weight, corrosion resistance, bendability,
formability and weldability. The strength of the AA5083 alloy can
be increased without significant loss in ductility by increasing
the Mg% in the alloy. However, increasing the % Mg in Al-Mg alloys
is accompanied by a drastic reduction in exfoliation and stress
corrosion resistances. Recently, a new alloy AA5383 has been
introduced with improved properties over AA5083 in both
work-hardened and soft tempers. In this case, the improvement has
been achieved primarily by optimising the existing composition of
AA5083 alloy.
[0004] Some other disclosures of Al-Mg alloys found in the prior
art literature will be mentioned below.
[0005] GB-A-1458181 proposes an alloy of strength increased
relative to JISH 5083, containing a larger amount of Zn. The
composition is, in wt %:
2 Mg 4-7 Zn 0.5-1.5 Mn 0.1-0.6, preferably 0.2-0.4 optionally, one
or more of Cr 0.05-0.5 Ti 0.05-0.25 Zr 0.05-0.25 impurities
.ltoreq. 0.5 balance Al.
[0006] In the examples, ignoring reference examples, the Mn
contents range from 0.19 to 0.44, and Zr is not employed. This
alloy is described as cold fabricatable, and also as suitable for
extrusion.
[0007] U.S. Pat. No. 2,985,530 describes an alloy for fabricating
and welding having a much higher Zn level than AA5083. The Zn is
added to effect natural age hardening of the alloy, following
welding. The composition for plate is, in wt %:
3 Mg 4.5-5.5, preferably 4.85-5.35 Mn 0.2-0.9, preferably 0.4-0.7
Zn 1.5-2.5, preferably 1.75-2.25 Cr 0.05-0.2, preferably 0.05-0.15
Ti 0.02-0.06, preferably 0.03-0.05 balance Al.
[0008] In "The Metallurgy of Light Alloys", Institute of
Metallurgy, Ser. 3 (London) 1983, by Hector S. Campbell, pages
82-100, there are described the effects of adding 1% of Zn to
aluminium alloys containing 3.5-6% Mg and either 0.25 or 0.8% Mn.
The Zn is said to improve tensile strength and to improve stress
corrosion resistance in ageing over 10 days at 100.degree. C. but
not in ageing over 10 months at 125.degree. C.
[0009] DE-A-2716799 proposes an aluminium alloy to be used instead
of steel sheet in automobile parts, having the composition, in wt
%:
4 Mg 3.5-5.5 Zn 0.5-2.0 Cu 0.3-1.2 optionally at least one of Mn
0.05-0.4 Cr 0.05-0.25 Zr 0.05-0.25 V 0.01-0.15 balance Al and
impurities.
[0010] More than 0.4% Mn is said to reduce ductility.
SUMMARY OF THE INVENTION
[0011] One object of the present invention is to provide an Al-Mg
alloy plate or extrusion with substantially improved strength in
both soft and work-hardened tempers as compared to those of the
standard AA5083 alloy. It is also an object to provide alloy plates
and extrusions which can offer ductility, bendability, pitting,
stress and exfoliation corrosion resistances at least equivalent to
those of AA5083.
[0012] According to the invention there is provided an
aluminium-magnesium alloy in the form of a plate or an extrusion,
having the following composition in weight percent:
5 Mg 5.0-6.0 Mn >0.6-1.2 Zn 0.4-1.5 Zr 0.05-0.25 Cr 0.3 max. Ti
0.2 max. Fe 0.5 max. Si 0.5 max. Cu 0.4 max. Ag 0.4 max. balance Al
and inevitable impurities.
[0013] By the invention we can provide alloy plate or extrusion
having higher strength than AA5083, and particularly the welded
joints of the present alloy can have higher strength than the
standard AA5083 welds. Alloys of present invention have also been
found with improved long term stress and exfoliation corrosion
resistances at temperatures above 80.degree. C., which is the
maximum temperature of use for the AA5083 alloy.
[0014] 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.
[0015] It is believed that the improved properties available with
the invention, particularly higher strength levels in both
work-hardened and soft tempers, result from increasing the levels
of Mg and Zn, and adding Zr.
[0016] The present inventors consider that poor exfoliation and
stress corrosion resistances in AA5083 may be attributed to the
increased extent of precipitation of anodic Mg-containing
intermetallics on the grain boundaries. The stress and exfoliation
corrosion resistances at higher Mg levels can be maintained by
precipitating preferably Zn-containing intermetallics and
relatively less Mg-containing intermetallics on the grain
boundaries. The precipitation of Zn-containing intermetallics on
the grain boundaries effectively reduces the volume fraction of
highly anodic, binary AlMg intermetallics precipitated at the grain
boundaries and thereby provides significant improvement in stress
and exfoliation corrosion resistances in the alloys of the present
invention at the higher Mg levels employed.
[0017] The alloy plates of the invention can be manufactured by
preheating, hot rolling, cold rolling with or without
inter-annealing and final annealing of an Al-Mg alloy slab of the
selected composition. The conditions are preferably that the
temperature for preheat in the range 400-530.degree. C. and the
time for homogenisation not more than 24 h. The hot rolling
preferably begins at 500.degree. C. Preferably there is 20-60% cold
rolling of the hot rolled plate with or without interannealing
after 20% reduction. The final and intermediate annealing is
preferably at temperatures in the range 200-530.degree. C. with a
heat-up period of 1-10 h, and soak period at the annealing
temperature in the range 10 min to 10 h. The annealing may be
carried out after the hot rolling step and the final plate may be
stretched by a maximum of 6%.
[0018] Details of extrusion processes are given below.
[0019] The reasons for the limitations of the alloying elements and
the processing conditions of the aluminium alloy according to the
present invention are described below.
[0020] All composition percentages are by weight.
[0021] Mg: Mg is the primary strengthening element in the alloy. Mg
levels below 5.0% do not provide the required weld strength and
when the addition exceeds 6.0%, severe cracking occurs during hot
rolling. The preferred level of Mg is 5.0-5.6%, more preferably
5.2-5.6%, as a compromise between ease of fabrication and
strength.
[0022] Mn: Mn is an essential additive element. In combination with
Mg, Mn provides the strength in both the plate and the welded
joints of the alloy. Mn levels below 0.6% cannot provide sufficient
strength to the welded joints of the alloy. Above 1.2% the hot
rolling becomes increasingly difficult. The preferred minimum for
Mn is 0.7% for strength and the preferred range for Mn is 0.7-0.9%
which represents a compromise between strength and ease of
fabrication.
[0023] Zn: Zn is an important additive for corrosion resistance of
the alloy. Zn 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 the intergranular corrosion resistance equivalent
to that of AA5083. At Zn levels above 1.5%, casting and subsequent
hot rolling becomes difficult especially at industrial scale. For
this reason the preferred maximum level of Zn is 1.4%. Because Zn
above 0.9% may lead to corrosion in a heat-affected zone of the
weld, it is preferred to use not more than 0.9% Zn.
[0024] Zr: Zr is important for achieving strength improvements in
the work-hardened tempers of the alloy. Zr is also important for
resistance against cracking during welding of the plates of the
alloy. Zr levels above 0.25% tend to result in very coarse
needle-shaped primary particles which decreases ease of fabrication
of the alloy and bendability of the alloy plates, and therefore the
Zr level must be not more than 0.25%. The minimum level of Zr is
0.05% and to provide sufficient strength in the work-hardened
tempers a preferred Zr range of 0.10-0.20% is employed.
[0025] 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%. A
suitable minimum level for Ti is 0.03%
[0026] 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 0.15-0.30%, more preferably
0.20-0.30%.
[0027] Si: Si forms Mg.sub.2Si which is practically insoluble in
Al-Mg alloys containing Mg>4.5%. Therefore Si limits the
beneficial effects of Mg. Si also combines with Fe to form coarse
Al-Fe-Si phase particles which can affect the fatigue life of the
welded joints of the alloy. To avoid the loss in primary
strengthening element Mg, the Si level must be not more than 0.5%.
The preferred range for Si is 0.07-0.20%, more preferably
0.10-0.20%.
[0028] 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 be not more than
0.3%. A preferred range for Cr is 0-0.15%.
[0029] Cu: Cu should be not more than 0.4%. Cu levels above 0.4%
gives rise to unacceptable deterioration in pitting corrosion
resistance of the alloy plates of the invention. The preferred
level for Cu is not more than 0.15%, more preferably not more than
0.1%.
[0030] Ag: Ag may optionally be included in the alloy up to a
maximum of 0.4%, preferably at least 0.05%, to improve further the
stress corrosion resistance.
[0031] The balance is Al and inevitable impurities. Typically each
impurity element is present at 0.05% maximum and the total of
impurities is 0.15% maximum.
[0032] Methods of making the products of the invention will now be
described.
[0033] The preheating prior to hot rolling is usually carried out
at a temperature in the range 400-530.degree. C. in single or in
multiple steps. In either case, preheating decreases the
segregation of alloying elements in the material as cast. In
multiple steps, Zr, Cr and Mn can be intentionally precipitated to
control the microstructure of the hot mill exit material. If the
treatment is carried out below 400.degree. C., the resultant
homogenisation effect is inadequate. Furthermore, due to
substantial increase in deformation resistance of the slab,
industrial hot rolling is difficult for temperatures below
400.degree. C. If the temperature is above 530.degree. C., eutectic
melting might occur resulting in undesirable pore formation. The
preferred time of the above preheat treatment is between 1 and 24
hours. The hot rolling begins preferably at about 500.degree. C.
With increase in the Mg % within the composition range of the
invention, the initial pass schedule becomes more critical.
[0034] A 20-60% cold rolling reduction is preferably applied to hot
rolled plate prior to final annealing. A reduction of at least 200
is preferred so that the precipitation of anodic Mg-containing
intermetallics occurs uniformly during final annealing treatment.
Cold rolling reductions in excess of 60% without any intermediate
annealing treatment may cause cracking during rolling. In case of
interannealing, the treatment is preferably carried out after a
cold reduction of at least 20% to distribute the Mg- and/or
Zn-containing intermetallics uniformly in the interannealed
material. Final annealing can be carried out in cycles of single or
multiple steps in one or more of heat-up, hold and cooling down
from the annealing temperature. The heat-up period is typically
between 10 min and 10 h. The annealing temperature is in the range
200-550.degree. C. depending upon the temper. The preferred range
is in between 225-275.degree. C. to produce work-hardened tempers
e.g. H321, and 350-480.degree. C. for the soft tempers e.g. O/H111,
H116 etc. The soak period at the annealing temperature is
preferably between 15 min to 10 h. The cooling rate following
annealing soak is preferably in the range 10-100.degree. C./h. The
conditions of the intermediate annealing are similar to those of
the final annealing.
[0035] In the manufacture of extrusions, the homogenisation step is
usually done at a temperature in the range 300-500.degree. C. for a
period of 1-15 h. From the soak temperature, the billets are cooled
to room temperature. The homogenisation step is carried out mainly
to dissolve the Mg-containing eutectics present from casting.
[0036] The preheating prior to extrusion is usually done at a
temperature in the range 400-530.degree. C. in a gas furnace for
1-24 hours or an induction furnace for 1-10 minutes. Excessively
high temperature such as 530.degree. C. is normally avoided.
Extrusion can be done on an extrusion press with a one- or a
multi-hole die depending on the available pressure and billet
sizes. A large variation in extrusion ratio 10-100 can be applied
with extrusion speeds typically in the range 1-10 m/min.
[0037] After extrusion, the extruded section can be water or air
quenched. Annealing can be carried out in batch annealing furnace
by heating the extruded section to a temperature in the range
200-300.degree. C.
EXAMPLES
Example 1
[0038] Table 1 lists the chemical composition (in wt %) of the
ingots used to produce soft and work-hardened temper materials. The
ingots were preheated at a rate of 35.degree. C./h to 510.degree.
C. Upon reaching the preheat temperature, the ingots were soaked
for a period of 12 h prior to hot rolling. A total hot reduction of
95% was applied. A reduction of 1-2% was used in the first three
passes of hot rolling. Gradually the% reduction per pass was
increased. The materials exiting the mill had a temperature in the
range 300.+-.10.degree. C. A 40% cold reduction was applied to the
hot-rolled materials. The final sheet thickness was 4 mm. Soft
temper materials were produced by annealing the cold-rolled
materials at 525.degree. C. for a period of 15 min. Work-hardened
temper materials were produced by soaking the cold-rolled materials
at 250.degree. C. for an hour. The heat-up period was 1 h. After
the heat treatments, the materials were air-cooled. The tensile
properties and corrosion resistances of the resultant materials are
listed in Table 2.
[0039] In Table 2, PS is proof strength in MPa, UTS is ultimate
tensile strength in MPa, and Elong is maximum elongation in %. The
materials were also assessed for pitting, exfoliation and
intergranular corrosion resistances. The ASSET test (ASTM G66) was
used to evaluate the resistances of materials to exfoliation and
pitting corrosions. PA, PB, PC and PD indicate the results of the
ASSET test, PA representing the best result. The ASTM G67 weight
loss test was used to determine the susceptibility of the alloys to
intergranular corrosion (results in mg/cm.sup.2 in Table 2).
Samples from welded panels of the alloys were tested to determine
tensile properties of welded joints.
[0040] The alloys which are examples of the present invention are
B4-B7, B11 and B13-B15. The other alloys are given for comparison.
AO is a typical AA5083 alloy. The compositions listed in Table 1
are grouped in such a way that those alloys with code beginning A
have Mg <5%, those alloys with code beginning B have Mg 5-6% and
those alloys with code beginning C above 6% Mg.
[0041] A simple comparison of the weld strengths of code A alloys
with the code B alloys clearly indicates that to obtain
significantly higher weld strengths, a Mg level in excess of 5% is
needed. Although increasing the Mg content results in an increased
weld strength, the fact that all the three code C alloys cracked
during hot rolling suggests that the ease of fabrication of the
alloys deteriorates significantly if the alloy has Mg level above
6%. Increasing Mg above 5% also causes an increased susceptibility
to intergranular corrosion as indicated by a weight loss value of
the B3 alloy which is 17 mg/cm.sup.2 (H321 temper). The
comparability of the weight loss values of the alloys B4-B7 with
those of the standard alloy AA5083 (alloy A0) indicates that an
addition of Zn in excess of 0.4% to alloys containing Mg >5%,
results in a significant improvement in resistance to intergranular
corrosion.
[0042] The ASSET test results of the alloys B1 and B2 suggest that
a Cu level in excess of 0.4% results in unacceptable level of
pitting corrosion and therefore the Cu level in must be kept below
0.4% to achieve a pitting/exfoliation resistance comparable to
those of AA5083. Although, excepting the Mn level, the compositions
of the alloys B9 and B5 are comparable, the strength values of B9
in the H321 temper are lower than those of B5 implying that to
obtain a higher strength, it is important to have a Mn level above
0.4%. However, severe cracking of the B10 alloy containing 1.3% Mn
during hot rolling implies that 1.3% represents the maximum limit
for increasing the strength in the H321 temper through Mn addition.
Experience gained during several trials indicate that a Mn level in
between 0.7-0.9% represents the compromise between strength
increase and difficulty in fabrication.
[0043] The properties of the alloys B11, B14 and B16 can be
compared to find the effect of Zr addition; the results for these
alloys indicate that the Zr addition increases both the strength in
the work-hardened temper and the strength of the welded joint. The
fact that the alloy B16 cracked during hot rolling implies that the
limit for Zr addition is below 0.3%. Large scale trials indicated
that the risk of forming coarse intermetallics is higher at Zr
levels above 0.2% and therefore, a Zr level in the range 0.1-0.2%
is preferred. The alloys B4, B5, B6, B7, B11, B13, B14 and B15
representing the invention have not only significantly higher
strength both before and after welding as compared to those of the
standard AA5083, but also have corrosion resistances similar to
those of the standard alloy.
6TABLE 1 Code Mg Mn Zn Zr Ti Fe Si Cr Cu Al A0 4.54 0.64 0.1 0.005
0.02 0.24 0.25 0.1 0.08 Remainder A1 4.22 0.6 0.1 0.004 0.01 0.25
0.25 0.09 0.3 " A2 4.3 0.6 0.1 0.04 0.02 0.24 0.25 0.1 0.6 " A3
4.38 0.65 0.1 0.13 0.01 0.25 0.27 0.09 0.05 " A4 4.26 0.64 0.1
0.215 0.02 0.25 0.27 0.09 0.05 " A5 4.33 0.65 0.1 0.01 0.01 0.27
0.28 0.24 0.06 " A6 4.3 0.64 0.1 0.005 0.02 0.23 0.28 0.24 0.3 " A7
4.2 0.6 0.1 0.145 0.01 0.25 0.29 0.24 0.3 " A8 4.4 0.63 0.1 0.145
0.01 0.23 0.29 0.24 0.07 " A9 4.7 0.8 0.4 0.13 0.14 0.23 0.14
<0.01 0.1 " A10 4.7 0.8 0.6 0.13 0.12 0.23 0.13 <0.01 0.1 "
A11 4.8 0.8 0.4 0.17 0.02 0.23 0.13 <0.01 0.1 " A12 4.8 0.8 0.4
0.25 0.13 0.25 0.12 <0.01 0.1 " B1 5.0 0.8 0.2 0.12 0.09 0.22
0.13 <0.01 0.4 " B2 5.0 0.8 0.2 0.12 0.06 0.23 0.12 <0.01 0.6
" B3 5.1 0.8 0.1 0.12 0.1 0.25 0.13 <0.01 0.1 " B4 5.2 0.8 0.4
0.12 0.13 0.25 0.13 <0.01 0.1 " B5 5.3 0.8 0.53 0.143 0.05 0.18
0.09 <0.01 0.06 " B6 5.2 0.8 1.03 0.13 0.05 0.18 0.09 <0.01
0.06 " B7 5.1 0.8 1.4 0.12 0.05 0.18 0.09 <0.01 0.05 " B8 5.2
0.8 1.7 0.12 0.04 0.17 0.09 <0.01 0.07 " B9 5.3 0.3 0.5 0.15
0.09 0.18 0.1 <0.01 0.1 " B10 5.2 1.3 0.4 0.12 0.05 0.17 0.09
<0.01 0.06 " B11 5.6 0.8 0.52 0.14 0.05 0.18 0.09 <0.01 0.05
" B12 5.7 0.8 0.2 0.12 0.08 0.25 0.13 <0.01 0.17 " B13 5.7 0.8
1.05 0.14 0.05 0.18 0.09 <0.01 0.05 " B14 5.9 0.8 0.4 0.23 0.12
0.25 0.13 <0.01 0.1 " B15 5.9 0.8 0.6 0.24 0.15 0.24 0.15
<0.01 0.1 " B16 5.8 0.8 0.4 0.3 0.1 0.24 0.15 <0.01 0.1 " C1
6.2 0.7 0.6 0.15 0.1 0.18 0.1 <0.01 0.09 " C2 6.5 0.8 1.9 0.15
0.07 0.18 0.1 <0.01 0.07 " C3 6.1 1.3 1 0.15 0.1 0.19 0.14
<0.01 0.07 "
[0044]
7 TABLE 2 H321 Temper 0 TEMPER WELD [H321] Corrosion Corrosion
Tensile properties resistance Tensile properties resistance Tensile
properties Code PS UTS Elong ASSET Wt loss PS UTS Elong ASSET Wt
loss PS UTS Elong A0 285 361 9.8 PA 5 150 295 21.1 PA 3 160 288 6.4
A1 281 359 10 PB/PC 2 155 305 23 PC 3 156 275 7 A2 286 361 9.8 PC
164 324 22.5 PC 2 155 270 6 A3 278 356 9.7 PA 2 155 299 20.8 PA 3
150 276 7 A4 279 354 8.8 PA 2 146 291 21.4 PA 3 153 278 6 A5 282
357 9.2 PA 2 155 309 19 PA 4 157 277 4 A6 290 359 9 PB/PC 2 158 310
18 PC 2 160 285 5 A7 289 365 10 PC 4 158 305 19.1 PA 4 161 285 6 A8
275 342 10.2 PA 3 160 299 19 PA 3 157 285 5 A9 329 394 8.8 PA 3 170
323 20.6 PA 2 162 290 6.2 A10 331 404 8.4 PA 2 176 332 21.4 PA 2
164 287 6.1 A11 326 398 9.8 PA 3 172 328 21.8 PA 3 163 290 6 A12
350 400 8.7 PA 2 168 322 21.3 PA 3 165 295 6 B1 329 404 8.5 PC/PD 5
181 341 21.1 PD 4 170 298 6 B2 337 405 8.7 PD 5 186 344 20.1 PD 7
171 307 6 B3 332 402 8.9 PB 17 179 326 19.7 PB 20 173 310 6 B4 326
404 9.7 PA 3 174 327 22.5 PA 2 187 310 6 B5 308 404 10.4 PB 8 174
342 21.2 PB 10 190 319 5.6 B6 314 416 10.6 PA/PB 4 175 344 22.7 PB
4 198 330 5.5 B7 320 421 10.2 PA/PB 5 173 340 22.3 PA 5 185 309 6
B8 CRACKED DURING CRACKED DURING ROLLING ROLLING B9 290 384 10.5 PB
12 170 321 21 PB 14 174 305 6 B10 CRACKED DURING CRACKED DURING
ROLLING ROLLING B11 318 395 10.1 PB 6 179 345 21.2 PB/PC 4 198 333
7.0 B12 328 419 9.7 PB 19 190 352 21.7 PB/PC 25 190 325 6 B13 322
428 10 PA/PB 7 176 344 18.9 PB 5 195 313 5.2 B14 331 427 9.7 PA 3
182 344 21.3 PA 2 199 327 6.2 B15 347 432 9.6 PA 2 187 356 22.4 PA
2 197 329 6.1 B16 CRACKED DURING CRACKED DURING ROLLING ROLLING C1
CRACKED DURING CRACKED DURING ROLLING ROLLING C2 CRACKED DURING
CRACKED DURING ROLLING ROLLING C3 CRACKED DURING CRACKED DURING
ROLLING ROLLING
Example 2
[0045] DC cast ingots with composition listed in wt % in Table 3
(alloy D1) were homogenised using the conditions of 510.degree.
C./12 h and hot rolled to plate of thickness 13 mm. The hot-rolled
plates were further cold rolled to 8 mm thickness.
8TABLE 3 Element Mg Mn Zn Zr Cu Fe Si Ti Cr Al Alloy 5.2 0.8 0.8
0.13 <0.1 0.2 0.1 0.024 <0.01 Remainder D1
[0046] The plates were subsequently annealed at 250.degree. C. for
a period of 1 h. The tensile properties and corrosion resistances
of the plates were determined. ASTM G66 and ASTM G67 were used to
assess susceptibilities to pitting and exfoliation and
intergranular corrosion. The properties of the alloy D1 before
welding are listed in Table 4 and compared with those of the
standard AA5083 alloy. Each item of data listed in Table 4 is an
average of ten tests carried out on samples produced from alloy D1.
It is obvious from Table 4 that the alloy D1 has not only
significantly higher proof and ultimate tensile strengths than the
standard AA5083 alloy but also has similar levels of resistance to
pitting, exfoliation and intergranular corrosion.
9 TABLE 4 Property AA5083 Alloy D1 Proof strength [MPA] 257 305
Ultimate Tensile Strength [MPa] 344 410 Elongation [%] 16.3 14
ASSET Test Result PB PA/PB Weight loss test result [mg/cm.sup.2] 4
5
[0047] 800.times.800 mm welded panels of the alloy D1 were produced
using a current and voltage of 190A and 23V respectively. Three
passes were used to produce the welded joints. 25 cross weld
tensiles were machined out from the welded panels. The filler wire
used was AA5183. For reference purposes, 25 cross weld tensiles
were machined out from similarly welded panels of the standard
AA5083 alloy. Table 5 lists the data derived from the 25 tensile
tests obtained from the 25 welded joints of each of the alloys
D1/5183 and 5083/5183, as average, maximum and minimum. It is clear
from the data in Table 5 that the alloy D1 has significantly higher
proof and ultimate tensile strengths as compared to those of the
standard AA5083 alloy in the welded condition.
10 TABLE 5 Alloy 5083/5183 Alloy D1/5183 PS UTS Elongation PS UTS
Elongation MPa MPa % MPa MPa % Average 139 287 17.2 176 312 15.8
Minimum 134 281 11.4 164 298 11.8 Maximum 146 294 21.9 185 325
21.1
Example 3
[0048] DC cast ingots with the same composition as alloy D1 of
Example 2 were homogenised using conditions of 510.degree. C./12 h
and hot rolled to plate of thickness 13 mm. The hot rolled plates
were further cold rolled to 8 mm thick plates. The plates were
subsequently annealed at 350.degree. C. for a period of 1 h. Thus
produced `O` temper plates were subsequently heat treated by
soaking samples at 100.degree. C. for various periods from 1 h to
30 days. For the reference purposes, samples from 8 mm, O temper
AA5083 plates were also heat treated in parallel to these samples
from alloy D1. The microstructures of the samples were
characterized using a scanning Electron Microscope. Examination of
the samples of AA5083 exposed to 100.degree. C. showed the
precipitation of anodic intermetallics on the grain boundaries. It
was also observed that as the exposure time at 100.degree. C. is
increased, the boundary precipitation becomes more intensive. It
becomes so intensive that eventually a continuous boundary network
of anodic intermetallics is resulted. However, unlike the case of
the standard AA5083 alloy, the samples of the alloy D1 were found
to contain precipitation of anodic intermetallics within the grains
even after prolonged exposure at 100.degree. C. Since it is known
that continuous boundary network of anodic intermetallics is
responsible for stress corrosion cracking, the use of the standard
AA5083 alloy is restricted to applications where service
temperature is less than 80.degree. C. However, since the chemistry
of the alloy D1 does not allow any continuous grain boundary
precipitation even after prolonged exposure at 100.degree. C., it
can be concluded that this alloy is suitable for use in
applications where service temperature is above 80.degree. C.
* * * * *