CA1043134A

CA1043134A - Aluminium base alloys

Info

Publication number: CA1043134A
Application number: CA190,403A
Authority: CA
Inventors: Edward F. Emley; Roger Grimes; Brian M. Watts; Michael J. Stowell
Original assignee: British Aluminum Co Ltd; TI Group Services Ltd
Current assignee: British Aluminum Co Ltd; TI Group Services Ltd
Priority date: 1973-01-19
Filing date: 1974-01-17
Publication date: 1978-11-28
Also published as: ATA41974A; NL172567C; FR2214755B1; AU6465774A; JPS49103814A; ES445208A1; NO138096B; ES422655A1; NL172567B; BE809910A; IT1006923B; SE403301B; DE2402351A1; NL7400642A; CH594738A5; ES445207A1; DE2402351C2; GB1445181A; FR2214755A1; NO740134L

Abstract

A B S T R A C T

An aluminium base alloy consists of a non-heat treatable base material containing aluminium and dynamic recrystallization modifying additives with at least one of Zr, Nb, Ta and Ni in solid solution. The alloy is superplastic.

Description

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 . ., 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, .; . : , . , - - ' : - , . : : , 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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1~)43134 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 ~, . .

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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.~ , ~43~34 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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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) . .
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 ::-Alloy Elongation (~/o) with optimum temperature conditions ".',' 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 , .:
~ 800C to produce a cell size in the cast alloy not exceeding . .

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- . :

- 1~43~L34 ; 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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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A superplastically deformable aluminium base alloy consisting of a non-heat treatable base material selected from the group consisting of:
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 a dynamic recrystallisation modifying additive respectively selected for each of these materials to achieve fine structure from the group of additives consisting of:
1) 0.4% to 2% iron and 0.4% to 2% silicon;
2) 0.4% to 1% iron;
3) nil;
4) 0.25% to 0.75% manganese;
and at least one of the elements Zr, Nb and Ta 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 remainder being normal impurities and known residual elements.

2. An alloy according to claim 1 in which said element Zr and the amount is not more than 0.8%.

3. An alloy according to claim 2 in which the amount is 0.4% to 0.7%.

4. A superplastically deformable aluminium base alloy consisting 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 and Ta 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 residual elements.

5. An alloy according to claim 4 in which the total content of iron and silicon is up to 2%.

6. An alloy according to claim 5 in which the iron and silicon are in equal proportions by weight.

7. A superplastically deformable aluminium alloy consisting of a non-heat treatable aluminium base alloy con-taining 0.75% to 2.5% manganese together with 0.4% to 1% iron and at least one of the elements Zr, Nb and Ta 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 residual elements.

8. An alloy according to claim 7 in which the manganese addition is in the range 1% to 2% with an iron content of at least 0.6%.

9. A superplastically deformable aluminium base alloy consisting of a non-heat treatable aluminium base alloy con-taining 0.25% to 0.75% manganese and at least one of the elements Zr, Nb and Ta 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 residual elements.

10. A superplastically deformable aluminium base alloy consisting of a non-heat treatable aluminium base alloy con-taining 1% to 4% magnesium together with 0.25% to 0.75%
manganese and at least one of the elements Zr, Nb and Ta 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 remainder being normal impurities and known residual elements.

11. An alloy according to claim 10 in which the manganese content is 0.3% to 0.5%.

12. An alloy according to claim 10, in which said total amount of Zr, Nb and Ta is not greater than 0.8%.

13. An alloy according to claim 12, in which said total amount is from 0.4 to 0.7%.

14. A method of making a superplastically deformable aluminium-base alloy semi-fabricated product comprising casting a liquid alloy having a composition according to claim 1 at a temperature of at least 775°C to produce a cell size in the cast alloy not exceeding 30 µM and subjecting the cast alloy to plastic working at a temperature not substan-tially in excess of 550°C.

15. A method as defined in claim 14 wherein the casting is carried out at a temperature in excess of 800°C.