Note: Descriptions are shown in the official language in which they were submitted.
9C~;~
The present invention relates to a cold wrought
aluminum alloy which has excellent ductility, corrosion
resistance and high strength and a mechanical strength hiyher
than conventional corrosion resistant aluminum alloys.
In general/ A~M~ type corrosion resistant aluminum
alloys have excellent mechanical properties and corrosion
resistance and accordingly, they have been used for large
structures such as buildings, ships and bridges.
However, these alloys have disadvantages of high
sensitivity for stress corrosion cracking because the inter-
metallic compound of Mg2AQ3 is easily precipitated in the grain
boundaries to cause grain boundary corrosion. Accordingly, in
the conventional AQ-Mg type cold wrought alloy having high
strength for example, the aluminum alloy in Japanese Industrial
Standard H 4000 and 5083, the content of ~Ig has been decreased
to overcome the disadvantages. However, these conventional i~
alloys have unsufficient mechanical strength for large struc-
tures. These alloys have disadvantages of low elongation, as
shown in the following Table 1. A~-Zn-Mg type ternary alloys
having age hardenability have been known as high strength
alloys which have excellent mechanical strength and weldability,
however these alloys have disadvantages of in~erior corrosion
resistance and stress corrosion cracking resistance.
The present invention provides a cold wrought aluminum
alloy which has excellent corrosion resistance and stress
corrosion cracking resistance and mechanical properties greater
than those o~ the conventional corrosion resistant aluminum
alloy.
Acco~din~ to the present inyention there is provided a
cold wrou~ht aliminum allo~ Whlch has excellent coxrosion
resistance and stress corro~on crackin~ resistance anld also
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excellent mechanical strength and elongation consistin~ essentially
of a cold wrought aluminum allo~ having essentially the following
composition: 4 - 7 wt.~ of ~g; more than 1 wt.% - 1.5 wt.% of Zn;
0.1 - 0.6 wt.% of Mn; at least one component selected from the group
consisting of 0.05 - 0.5 wt.% of Cr, 0.05 - 0.25 wt.% of $i and
0.05 - 0.25 wt.% of Zr; and less than 0.5% of impurities, the
balance being aluminum. The impurities are mainly Fe and Si and
less than 0.1 wt.% of other impurities. This alloy is useful for
large constructions such as buildings, ships and bridges. ¦
In said alloy, Cr can be substituted by 0.05 - 0.25 wt.
% of Ti and 0.05 - 0.25 wt.% of Zr, give excellent corrosion
resistance, stress corrosion cracking resistance and mechanical
strength. At least one of 0.05 - 0.25 wt.~ o Ti and 0.05 - 0.25 wt.
% of Zr can be added to said alloy containing Mn, to improve
m~chanical strength.
The aluminum alloy o the presenk invention contains
said components and has excellent corrosion resistance and high
strength and is cold workable. The aluminum alloy is prepared
without heat treatment for ageing and precipitating effect.
The mechanical strength of the alloy is improved but,
workability and corrosion resistance are decreased by increasing
magnesium content. Accordingly, the magnesium content is 4 - 7
wt.% preferably 4.5 - 6.5 wt.% to the alloy.
The mechanical strength of the alloy is not affected
by the zinc content. Zinc is added to improve workability and to
prevent grain boundary corrosion caused by grain boundary precipit-
ation of Mg2A~3. An adverse affect of corrosion resistance and
an age hardening phenomenon are found with more than 1.5 wt.% of
zinc. Accordingly, the zinc content is more than 1.0 - 1.5 wt.%.
$he mechanical properties of strength and elongation,
corrosion resistance, and stress corrosion cracking resistance of
the alloy are remarkably improved by adding chromium anld manganese.
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The chromium and manganese content is 0.05 - 0.5 wt. %
preferably 0.1 - 0.3 wt.%of Cr; or 0.1 - 0.6 wt.%, preferably :
0.2 - 0.4 w-t.% of Mn; or 0.3 - 0.5 wt.% of ta-tal o-f Cr ~ Mn. -
A coarse intermetallic compound is formed which adversely
affects the mechanical properties and cold workability and
corrosion
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resistance of the alloy with an excess of Cr and/or Mn.
The mechan:ical strength, corrosion resistance and stress -~
corrosion cracking resistance of the alloy are remarkably improved
by adding titanium or zirconium as the addition of chromium or
manganese. The titanium and zirconium content is 0.05 - 0.25 wt.%
preferably 0.07 - 0.15 wt.~.
An alloy having excellent elongation, corrosion resist-
ance and stress corrosion cracking resistance similar to those
of additions of Mn and improved mechanical strength superior to
that of addition of Mn can be obtained by adding both of Mn and
Ti or Zr.
It is possible that the alloy may contain small content
or impurities such as iron or silicon as in conventional aluminum
alloys. However, the corrosion resistance and mechanical proper-
t~es of the alloy are adversely affected by the impurities.
Accordingly, it is preferable to decrease the impurities content
to less than 0.4 wt.~. The impurities except iron and silicon is
less than 0.01 wt.~ of each impurity and is less than 0.1 wt.%
of -total of impurities. Thus, the aluminum alloys of the present
invention do not contain components in suhstantia~ amounts except
AQ, Mg, Zn, Cr, ~n, Ti, Zr, Fe and Si.
The test results for various aluminum alloys of the
present invention are given in the following Example for showing
the characteristics of the alloys.
[Example]
Each aluminum alloy slab was prepared by casting each
molten aluminum alloy having the formulation of Table 1 at the
casting temperature of 750C in a permanent mould having mould cav-
ity of150n~ x llOmm x`30 mm. The slab was scalped, was then homo-
genized at 430C for 24 hourst was treated by a hot rolling at
the same temperature, the product was then further treated by a
cold rolling after surface washing to form a rolled product having
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thickness of 1.5 - 2 ~, and the rolled product was annealed at
about 370C during 5 hours. The annealed product was used for
various tests as softened alloy. The annealed product was treated
by a cold rolling mill to give hardness of ]/4 ~1, and used for
various tests as strain hardened alloy. The test methods are
as follows.
(a) Tests for ultimate strength,
0.2% proof stress and elongation:
Japanese Industrial Standard Z 2201:
(b) Corrosion resistance test:
Japanese Industrial Standard D 0201.
(semi-immersing in artificial sea water for 6 months)
The test pieces were ~sed for observation of corrosion
on the surface after corrosive treatment, as well as
for mechanical strength tests.
~tr_ss corrosion cracking test:
Corrosive solution: aqueous solution of 5% NaCQ
0.3% H2O2
Load: 70Q weight for 0.2% proof stress
Time: Time to breaking (hr.)
No breaking ones; 4000 - 5000 hr.
Note: (in following Tables)
O: Softened alloy
H: ~ Strain hardened alloy (corresponding to 1/4H)
Sample Nos. 13 15: Reference alloy (15; 5083 alloy)
~ _
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Z
Table 1
_ . mechanical properties
formulation(%) (%) _
~ ultimate elon~a-
;~mple Mg. ~n Mn Cr Type strength 0.2 proof tion
No . kg/mm 2 %
30.7 1 14.3 ` 31.0
5.0 1.0 0.44 _ _
H33.4 24.4 18.9
~ O31.7 15.3 33.6
2 5.4 1.4 0.190.16
H34.6 25. 3 20. 5
33.9 1 16.0 30.0
3 6.2 1.0 0.44 _
.. H 36.9 2 6.6 21.0
O 33.1 15.9 32.1 _
4 6.5 0.72 0.200.15 _
EI 36.4 25.1 23.4
_ _ __ _ ;-o 33.0 15.2 31.5
6.4 1.3 0.200.14 __ l
H 37.1 26.0 22.8
~_ __ _ _ _ ' O 3~ .7 - lS.9 29.8
6 6.6 1.6 0.220.15
H 38. 6 28.6 18.9
~ ' O-- -34.5 19.5 25.0
7 5.5 1.1 0.34 _
EI 35.9 27.9 16.8
_ _ O 39.5 24.2 19.8
! 8 5.6 1.0 0.34 _ _
H 42.8 34.1 15.3
O 30.5 15.4 32.3
5.1 1.0 _ _ _
H 3 3. 6 24.9 20. 3
_ O 33.3 18.7 23.0
10 5 . O 1 . O _ _ __ _.
H 36.1 27.9 15 ~ 8
O 26.8 12.3 30.
5.0 1.0 _ _
H 33.2 ¦ 28.0 12,3 ~ -
_ _ O 29.3 1 13.3 32.8 ~
12 6~2 1.0 _ _ ~ -
H 36.1 30.8 14.S
_ ' O 29.4 15.7 2~ . ~
13 4.5 _ 0.540.17 _ _ _ .~ _ . _ H 36.5 33.0 ~ :9:.,0 ., :';
.. - .
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Table 2 ~-
Sampl~ formulation (%) iType corrosion 'time to stress
No. _ resistance 'corrosion
test rating~cracking :
Mg Zn Mn Cr nu~er ~ (hr)
O 9 I > 4000
1 5.Q 1.0 0.44 _
H 9 >4000
O 9 ~S000
2 5.4 1.4 0.19 0.16 _
EI 9 ~ 5000
..
: O 8 ~4000
3 6.2 1.0 0.44 _ _ _
. H 7 >4000
_
. O 9 > 5000
4 6.5 0.72 0.20 0.1$
H . 9 ~ 5000
__ _
O . 9 ~ 5000
5 6.4 1.3 0.20 0.14 _
H 9 ~5000
_ ~__ _ .
O ~ ~5000
6 6.6 1.6 ! 0.22 0.15 _ . _
. H B ~5000
. .
O 9 >4000
7 5.5 1.1 0.34 _ .
H 9 >4000
. _ __
O 8 >4000
8 5.6 1.0 0.34 _
H . 8 ~4000
_ _
O 9 _
9 5~1 1.0 ~ _
H 9 _ . .
_ _ _
O ~ _
5 . O 1 . O _ _ _
H 8 _ :
_ __. ., .
O 8 2000 : -
115.0 1.0 _ _
H 8 1000
.
O 7 1000
126.2 1.0 ._ _
: H 7~ 800
_ _
: O 8 2000
134.5 _ ~.54 0.17 _ _ _ ::
H 7 1000
_ _ _ ' ' ' ~. ' '
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As shown in Table 1, the 0.2% proof stress of the
softened alloy was substantially increased by adding Mn or both
Mn and Cr. comparing to that of the reference. The elongation
of the strain hardened allov was substantially improved by
adding Mn or both Mn and Cr to be twice as high as that of the
concentional 5083 alloy. The ultimate strength of the alloy
containing about 6% of Mg is especially high.
The aluminum alloys of the invention have excellent
mechanical properties and high ductility compared to the conven-
tional corrosion resis-tant alloys, and accordingly, the aluminum
alloys of the present invention have high value as an aluminum
alloy ~or construction purposes. The mechanical s-trength of the
alloy can be changed depending upon a content of Mg, and
ac~ord:ing:ly the aluminum alloys can be used for var~ous appli~
cations.
The corrosion resistance and stress corrosion cracking
resistance of alloy can be substantially improved by adding
Mn or both Mn and Cr. Typical examples are given in Table 2.
As shown in the reference, the A~-Mg-Zn alloy contain-
ing no Cr or Mn have corrosion resistance and stress corrosion
cracking resistance which are same or lower than -those of the
conventional corrosion resistan-t alloy of the 5083 alloy.
~lowever, the corrosion resistance and stress corroslon cracking
resistance are substantially improved by adding Cr or Mn.
Although there is no example in Table 2, the alloys
containing more than 1.5% of;Zn have inferior workability and
inferior corrosion resistance which are not higher -than those of
the S085 alloy even though Mn and Cr is added. Moreover, ageing
and precipitation hardening phonomenon is found in alloys con-
taining more than 1.5% of Zn. Accordingly they are not suitable
as an alloy for fabrica-tion. The mechanical streng-th corrosion
resistance and stress corrosion cracking resistance are improv-
ed by adding 0.05 - 0.25% of Ti or Zr or both o~ them ins-tead
o~ Cr
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The excellent properties of the aluminum alloys of the
invention, as an extrudable alloy were compared to those of the
references by measuring each resistance to plastic deformation.
The results are shown in Figure 1 which illustrates graphs of
resistance to plastic deformation plotted against reduction -
in cross section area for cast and forged alloys respectively
of three AQ-containin~allo~s.The relation of the r~sistance to
plastic deformation (Kg/mm2) (ordinate) and the reduction of
sectional area (%)(abscissa) for the samples prepared by casting
(upper graph) and for the samples prepared by forging 50% (lower
graph) are shown in Figure 1 wherein
o Mg: 5.4%, Zn: 1.1%, Mn: 0.18~, Cr: 0.1~%
Mg: 6.3~ Zn: 1.1% Mn: 0.19%, Cr: 0.15
x 5056 alloy.
The aluminum alloy containing 5.4~ oE Mg, 1.1'~ of Zn,
0.18~ of Mn and 0.14~ of Cr, and the aluminum alloy containing
6.3% of Mg, 1.1~ of Zn, 0.19% of Mn, and 0.15% of Cr and the 5056 ~
corrosion resistant aluminum alloy containing 5.4% of Mg were :
used for the tests.
The test method is as follows:
The alloys were respectively cast in each cylindrical
permanent mould having mould cavity diameter of 60 mm and height
of 200 mm. Each o cylindrical sample having diame~er of 15 mm
and height of 18 mm was cut off from the center of the cast
product. The results are shown in the upper graph.
Other cast product was forged by 50~, and then each of
c~lindrical sample having diameter of 15 mm and height of 18 mm ~;
was cut off from the center of the product. The results are
shown in the lower graph.
The compressing tests of each group of the samples were
conducted at ~30C.
From the results, it is clear that the aluminum alloys
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of the present invention have superior workability to that of
the 5056 alloy.
In accordance with the tests for extruding ~ach alum-
inum alloy billet containing 6~1% of Mg, 1.0% of Zn, 0.13% of
Cr and 0.13% of Mn, the pressure required for extrusion was lower
than that of the 5083 alloy and the formation of pick up was
smaller than that of the 5083 alloy. In accordance with the
tests for extrusion at 530C in two heating steps (at 430C for
4 - 5 hours and then at 530C), the extrusion velocity for the
alloy of the invention was higher than two times of tha-t of the
5083 alloy.
The aluminum alloy of the invention is also suitable as
an extrudable alloy.
In addition, the alloy oE the invention shows so good
weldability as 85~ of efficiency of joint in the welding test.
Formulation
5056 alloy 5083 alloy
Mg 5.4 wt.% Mg 4.5 wt.%
Mn 0.0~ " Mn 0.54 "
Cr 0.1 " Cr 0.17 "
