GB1596918A - Super plastic aluminium base alloys - Google Patents

Description

(54) IMPROVEMENTS RELATING TO SUPERPLASTIC ALUMINIUM BASE ALLOYS (71) We, THE BRITISH ALUMINIUM COMPANY LIMITED, a Company registered under the laws of Great Britain of 7 Baker Street, London WIM 1AB, and formerly of Norfolk House, St. James's Square, London, S.W.1, England, and T.I. (GROUP SERVICES) LIMITED, a Company registered under the laws of Great Britain of T.I. House, Five Ways, Edgbaston, Birmingham, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates 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 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 high 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 a=ki" where a represents flow stress k a constant, É strain rate and m strain rate sensitivity index.

In British Patent No. 1,387,586 there is proposed a superplastically deformable aluminium-base alloy consisting of an aluminium-base alloy selected from non-heat treatable aluminium-base alloys containing at least 5% Mg or at least 1% Zn and heat treatable aluminium-base alloys containing one or more of the elements Cu, Mg, Zn, Si, Li and Mn in known combination and quantities, and at least one of the elements Zr, Nb, Ta and Ni in a total amount of at least 0.30% substantially all of which is present in solid solution, said total amount not exceeding 0.80%, the remainder being normal impurities and incidental elements known to be incorporated in the said aluminium-base alloys.

In the alloys and processes of the two preceding paragraphs the ability of the material to undergo superplastic deformation appears to be dependent on two factors (a) the presence of alloying additions to the aluminium which enable controlled dynamic recrystallisation to occur and (b) a fine dispersion of ZrAl3 or other phase which restricts the growth of newly formed grains. Of the elements Zr, Nb, Ni and Ta which were suggested to produce the dispersed phase, the use of zirconium alone is preferred.

The present invention provides a modification of the invention claimed in British Patent 1,387,586.

According to one aspect of the present invention there is provided a superplastically deformable aluminium-base alloy comprising a modification of any one of Claims 1 to 14 of Patent No. 1,387,586 in which the dispersion producing elements Zr, Nb, Ta, and Ni are replaced by either 1. 1.0% to 3.0% Hf or 2. Hf and at least one of the elements Zr, Nb, Ta and Ni, the sum of the contents of Zr, Nb, Ta and Ni together with one quarter of the Hf being at least 0.25% but not more than 1.0%.

When the dispersion producing element consists of Hf the content may be between 1.2% and 2.0%. When the dispersion producing elements are in accordance with numbered part 2 above the sum is preferably at least 0.3?,',) but not more than 0.8% and when, as is preferred, the elements consist of Hf and Zr the minimum Hf content is advantageously 0.25%. Minor elements which may be added with benefit or at least tolerated include Ti, B and Be in amounts up to 0.20%, 0.05% and 0.01% respectively. Small amounts of one or more of the elements Ca, Sn, Bi, Pb, Cr, Ge, Cd, Ag, and Sb may also be added in amounts not exceeding 0.25% individually or 0.75% in total.

The invention also provides a method of making a superplastically deformable aluminium-base alloy according to any one of Claims 15 to 20 of Patent No.

1,387,586 in which the liquid alloy has a composition according to either one of the preceding paragraphs.

Additionally the invention provides an article according to any one of Claims 21 to 24 of Patent No. 1,387,586 in which the alloy has a composition according to either one of the penultimate two paragraphs of this specification.

It has been found that hafnium may be used instead of or with one or more of the dispersion producing elements disclosed in the Complete Specification of Patent No. 1,387,586 within the various limits set out above and the contents of the above numbered specification may be read in relation to hafnium where appropriate.

Minor elements which may be added with benefit or at least tolerated include Ti, B and Be in amounts up to 0.20%, 0.05% and 0.01% respectively. Small amounts of one or more of the elements Ca, Sn, Bi, Pb and Sb may also be added in amounts not exceeding 0.25% individually or 0.75% in total.

By way of example an alloy containing 6% Cu and 1.3% Hf was cast and processed in a manner similar to that used for obtaining the data given in Tables B and E of British Patent No. 1,387,586. The results are compared with the data taken from these tables in Table I below.

TABLE I Alloy Composition (%) Maximum Elongation (%) Al6% Cu 127 Al6% Cu0.5% Zr 315410* Al6% Cu1.3% Hf 415 Criterion for superplasticity 200 (minimum) *Data from Tables B and E of British Patent No. 1,387,586.

It will be seen therefore that hafnium is effective in conferring superplastic behaviour upon Al6% Cu alloy.

Further data relating to other alloys is set out in Table II below.

TABLE II Alloy Composition (%) Maximum Elongation (%) Al-6% Cu0.25% Hf0.20% Zr 224 Al-6% Cu-0.72% Hf-0.21% Zr 798 Al-6% Zn0.8% Mg-I .5% Hf 220 Al7% Zn-l.0% Mg-0.75% Hf-0.21% Zr 415 WHAT WE CLAIM IS:- 1. A superplastically deformable aluminium-base alloy comprising a modification of any one of Claims 1 to 14 of Patent No. 1,387,586 in which dispersion producing elements Zr, Nb, Ta and Ni are replaced by either 1. 1.0% to 3.0% Hf or 2. Hf and at least one of the elements Zr, Nb, Ta and Ni, the sum of the contents of Zr, Nb, Ta and Ni together with one quarter of the Hf being at least 0.25% but not more than 1.0%.

2. An aluminium-base alloy according to Claim 1 in which when the dispersion producing element consists of Hf the content is between 1.2% and 2.0%.

3. An aluminium-base alloy according to part 2 of Claim 1 in which the sum is at least 0.3% but not more than 0.8%.

4. An aluminium-base alloy according to part 2 of Claim 1 or Claim 3 in which said elements consist of Hf and Zr with the minimum Hf content being 0.25%.

5. An aluminium-base alloy according to any one of the preceding claims containing Ti, B or Be in amounts not exceeding 0.15%, 0.05% and 0.01% respectively.

6. An aluminium-base alloy according to any one of the preceding claims containing one or more of the elements Ca, Sn, Bi, Pb or Sb in amounts not exceeding 0.25% individually and 0.75% in total.

7. A method of making a superplastically deformable aluminium-base alloy according to any one of Claims 15 to 20 of patent No. 1,387,586 in which the liquid alloy has a composition according to any one of Claims I to 6.

8. An article according to any one of Claims 21 to 24 of Patent No. 1,387,586 in which the alloy has a composition according to any one of Claims 1 to 6.

9. An aluminium-base alloy according to Claim I substantially as herein described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. TABLE II Alloy Composition (%) Maximum Elongation (%) Al-6% Cu0.25% Hf0.20% Zr 224 Al-6% Cu-0.72% Hf-0.21% Zr 798 Al-6% Zn0.8% Mg-I .5% Hf 220 Al7% Zn-l.0% Mg-0.75% Hf-0.21% Zr 415 WHAT WE CLAIM IS:- 1. A superplastically deformable aluminium-base alloy comprising a modification of any one of Claims 1 to 14 of Patent No. 1,387,586 in which dispersion producing elements Zr, Nb, Ta and Ni are replaced by either

1. 1.0% to 3.0% Hf or

2. Hf and at least one of the elements Zr, Nb, Ta and Ni, the sum of the contents of Zr, Nb, Ta and Ni together with one quarter of the Hf being at least 0.25% but not more than 1.0%.

2. An aluminium-base alloy according to Claim 1 in which when the dispersion producing element consists of Hf the content is between 1.2% and 2.0%.

3. An aluminium-base alloy according to part 2 of Claim 1 in which the sum is at least 0.3% but not more than 0.8%.

4. An aluminium-base alloy according to part 2 of Claim 1 or Claim 3 in which said elements consist of Hf and Zr with the minimum Hf content being 0.25%.

5. An aluminium-base alloy according to any one of the preceding claims containing Ti, B or Be in amounts not exceeding 0.15%, 0.05% and 0.01% respectively.

6. An aluminium-base alloy according to any one of the preceding claims containing one or more of the elements Ca, Sn, Bi, Pb or Sb in amounts not exceeding 0.25% individually and 0.75% in total.

7. A method of making a superplastically deformable aluminium-base alloy according to any one of Claims 15 to 20 of patent No. 1,387,586 in which the liquid alloy has a composition according to any one of Claims I to 6.

8. An article according to any one of Claims 21 to 24 of Patent No. 1,387,586 in which the alloy has a composition according to any one of Claims 1 to 6.

9. An aluminium-base alloy according to Claim I substantially as herein described.