Note: Descriptions are shown in the official language in which they were submitted.
1()43~34
BACKGROUND OF THE INVENTION
; This invention relates to aluminium-base alloys,
and more particularly to aluminium-base alloys capable of
being formed or shaped into objects by superplastic
deformation.
It is known that certain alloys under certain
conditions can undergo very large amounts of deformation
without failure, the phenomenon being known as superplAsticity
and characterised by a high strain rate sensitivity index in
the material as a result of which the normal tendency of a
; 10 stretched specimen to undergo preferential local deformation
` ("necking") is suppressed. Such large deformations are
moreover possible at relatively low stresses so that the
forming or shaping of superplastic alloys can be performed
more simply and cheaply than is possible with even highly
--~ 15 ductile materials which do not exhibit the phenomenon. As a
convenient numerical criterion of the presence of
superplasticity~ it may be taken that a superplastic material
will show a strain rate sensitivity ("m"-value) of at least
0.3 and a uniaxial tensile elongation at temperature of at
least 200%, "m"-value being defined by the relationship
6= ~ where 6 represent~ flow streqs, ~ a constant,
strain rate and ~ strain rate sensitivity index.
No known aluminium-base alloy can be superplastically
deformed other than the Al-Cu eutectic composition which
contains 33% copper and has neither the low density nor the
good corrosion resistance characteristic of aluminium alloys.
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1~4;~34
In the Complete Specification of Canadian Patent
Application S.N. 147,541 filed July 20, 1972, aluminium base
alloys are described which can be superplastically deformed.
; These include non-heat treatable alloys containing at least
5% magnesium or at least 1% zinc, together with at least
`~ one of the elements Zr, Nb, Ta and Ni in a total amount of
~ 0.3% to 0.8% substantially all of which is present in solid
; solution.
It was not found possible, by inclusion of even
considerable amounts of zirconium in the desired form, to
induce superplastic behaviour in pure aluminium or the
1-1 1/4% Mn alloys or in Al-Mg alloys containing a few per
cent only of magnesium, although these are the cheapest and
most widely used types of aluminium alloy for production of
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formed components.
'~ According to one aspect of the present invention
- a superplastically deformable aluminium base alloy consists
of a non-heat treatable base material selected from the
group consisting of:
-~ 20 1. Aluminium of normal commercial purity;
2. Aluminium and 0.75 to 2.5% manganese;
3. Aluminium and 0.25 to 0.75% manganese; and
4. Aluminium and 1 to 4% magnesium;
together with dynamic recrystallisation modifying additives
for these materials to achieve fine structure respectively
consisting of:
1. 0.4% to 2% iron and 0.4% to 2% silicon;
2. 0.4% to 1% iron;
; 3. nil;
30 4. 0.25% to 0.75% manganese,
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1043134
and at least one of the elements Zr, Nb, Ta and Ni in an
amount of at least 0.3% substantially all of which i8
present in solid solution, the total amount of said element~
not exceeding 1% and the remainder being norma~ impurities
and known incidental elements. The preferred one of said
elements is Zr and the amount is advantageously not more
than o.8% and preferably 0.4% to 0.7%.
~ According to another aspect of the present invention
; a superplastically deformable aluminium base alloy consists
of aluminium of normal commercial purity together with 0.4%
- to 2% iron and 0.4~ to 2% silicon and at least one of the
elements Zr, Nb, Ta and Ni in an amount of at least 0.3%
substantially all of which is present in solid solution the
total amount of said elements not exceeding 1% and the balance
being normal impurities and known incidental elements. The
total content of iron and silicon should preferably be 0.75%
to 2% and they should preferably be in equal proportions by
weight.
According to yet another aspect of the present
~0 -invention a superplastically deformable aluminium base alloy
consists of a non-heat treatable aluminium base alloy
containing 0.75% to 2.5% manganese together with 0.4% to
1% iron and at least one of the elements Zr, Nb, Ta and Ni
in an amount of at least 0.3% substantially all of which is
present in solid solution, the total amount of said elements
not exceeding 1% and the balance being normal impurities and
known incidental elements. The manganese addition should
preferably be in the range 1% to 2% with an iron content of
at least o.6%.
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According to a further aspect of the present invention
a superpla~tically deformable aluminium base alloy consi~ts
of a non-heat treatable aluminium base alloy containing 0.25~
to 0.75% manganese and at least one of the element~ Zr, Nb, Ta
and Ni in an amount of at least 0.3% substantially all of which
is present in solid solution, the total amount of said
elements not exceeding 1% and the balance being normal
impurities and known incid~ntal elements.
According to yet a further aspect of the pre~ent
invention a superplastically deformable aluminium base alloy
consist~ of a non-heat treatable aluminium base alloy containing
1% to ~% magnesium together with 0.25% to 0.75% manganese and
at least one of the elements Zr, Nb, Ta and Ni in an amount of
at least 0.3% substantially all of which i~ present in solid
solution, the total amount of said elements not exceeding 1%
and the remainder being normal impurities and known incidental
elements. Preferably the manganese content is 0.3~ to 0.5%.
In another a~pect the present invention provides a ~ ~
superplastically deformable aluminium alloy consisting of a ~ i
non-heat treatable aluminium base alloy capable of dynamic
recrystallisation to a fine structure during hot deformation,
and at least one of the elements Zr, Nb, Ta and Ni in an amount
of at least 0.3% substantially all of which is present in solid
~olution, the total amount of said elements not e~ceeding 1.0%
and the balance being normal impurities and known incidental
elements. The base alloy may con~ist of aluminium of normal
commercial purity containing from 0.4 to 2% Fe and 0.4 to 2%
Si. Preferably the alloy contains a total of from 0.75
to 2% of Fe and Si and ideally it contains
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4313~
equal proportionq by weight of Fe and Si.
The base alloy may consist of aluminium containing
from 0.75 to 2.5% of Mn and from 0.4 to 1% of Fe and
preferably contains from 1 to 2% of Mn and at leact o.6%
~ 5 Or Fe.
The base alloy may consist of aluminium and from
,1 ,.
~ 0.~5 to 0.75% of Mn and preferably contains from 0.3 to
- i
0.5% of Mn. In addition the alloy may contain from 1 to
- 4% of Mg. The total amount of Zr, Nb, Ta and Ni should
preferably not exceed o.8% and ideally is from 0.4 to 0.7%.
According to a further feature of the present
invention, a method of making a superplastically deformable
aluminium-base alloy semi-fabricated product comprise~
casting a liquid alloy having a compo~ition according to
any one of the immediately preceding five paragraphs at a
temperature of at least 775C and preferably in excess of
800C to produce a cell size in the cast alloy not
,. ,
exceeding 30/uM and ~ubjecting the cast alloy to plastic
working at a temperature not substantially in excess of
550C.
In the alloy of the present invention, in addition
to normal impurities, such as silicon where thi~ element
- i3 not required as a ~pecified constituent~ common
incidental elements for example beryllium, titanium and
boron, may be added to achieve known effects, for example
to control oxidation or effect grain refinement of the
cast ~tructure.
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By cell size is meant secondary dendrite arm
. spac ing .
Throughout this specification all percentages are by
weight.
Investigations of the mechanism by which superplastic
behaviour is achieved in the alloys of Canadian Patent
Application S.N. 147,541 indicated that some dynamic
recrystallisation was taking place during the course of the
superplastic deformation whereas alloys which were recrystallised
prior to the hot forming operation and those which remained
unrecrystallised after hot forming did not exhibit superplasticity.
; With this information it was possible to prescribe additional
; elements which, by reducing the high stacking fault energy of
aluminium, would advance recrystallisation and enable some
15 dynamic recrystallisation to a fine structure to take place ~-
during hot deformation in the case of the pure aluminium and
the Al-l 1/4%Mn alloy. Similarly it was possible to prescribe
additions to retard recrystallisation to a fine structure in
the case of the low alloyed Al-Mg alloys. When these
recrystallisation-controlling additions were made to these
three kinds of alloy which, with zirconium additions alone,
could not previously be made superplastic, all three materials
could be superplastically deformed as shown by the results of
Table 1.
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43134
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TABLE 1
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AlloyAdditives to modify Elongation (%) with
Typedynamic recry ~tallisation optimum temp.
By advancing By retarding conditions
; recrystall- recrystall- Without With
isationisation recrystn- recrystn-
- controlling controlling
addn. addn.
10Pure Al 0.8%Fe+0.8%Si _ 172 440
(+0.5%Zr)
Al-1~%Mn 0.6Fe _ C200 448
(~0.5%Zr)
. . :,
Al-2%Mg _ 0.3%Mn 170 300
(+0.5%Zr)
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Alternatively, in the case of Al-Mn alloys dynamic
recrystallisation could be encouraged by reducing the manganese
content~ in which situation it ~as not necessary to make any
further addition apart from zirconium. These alloys of
- 20 lower manganese content could then be superplastically
deformed as shown by the results of Table 2.
~ABLE 2
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Alloy Elongation (~/o) with
optimum temperature conditions
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Al-0.6%Mn-0.5%Zr 400
Al-0.3%Mn-0.5%Zr 356
The alloys of the present invention should be cast
at a temperature of at least 775 C and preferably in excess of
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~ 800C to produce a cell size in the cast alloy not exceeding
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; 30 /uM. The case alloy may then be subjected to plastic
working at a temperature not substantially in excess of 550C.
The present invention provides superplastically deformable
aluminium base alloys which are (apart from their super-
plasticity) not only of a cheap type of alloy but are also
-- those which are generally known to producers of conventionally
formed components.
If desired the alloys may be subjected to a conventional
cold forming operation either before or after superplastic
- 10 deformation.
- It will be understood that although only the addition
of Zr has been illustrated above the use of Nb, Ta and Ni as
disclosed in Canadian Patent application S.N. 147,541 is also
envisaged.
It will also be understood that when the cast alloy
- is subsequently rolled or otherwise formed the percentage of
Zr, Nb, Ta and Ni which remains in solid solution may be ~-
changed. --
Whether the rolled or otherwise formed alloy remains
superplastic will depend both upon the residual quantity of
Zr, Nb, Ta and Ni which remains in solid solution and the
amount of grain refining caused by some of the Zr, Nb, Ta
and Ni coming out of solid solution.
Thus a cast alloy according to the present invention may
: .................................................................... .. .. - ..
be partially formed by various processes and retain the
properties of superp]asticity.
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