US2604396A - Magnesium base alloys - Google Patents

Description

Patented July 22, 1952 MAGNESIUM BASE ALLOYS Alfred C. Jessup, Clifton Junction, near Manchester, England, assignor to Magnesium Elektron Limited, Clifton Junction, near Manchester, England, a British company No Drawing. Application May 21, 1951, Serial No. 227,541. In Great Britain June 2, 1950 y This invention relates to magnesium'base al-, loys.

3 Many attempts have been made to produce magnesium base alloys having high resistance to creep atelevated temperatures. To this end, it has been proposed to use binary alloys containing up to about cerium, or to produce alloys containing cerium together with certain other elements, for example, manganese, cobalt and calcium. While such additions of cerium have proved effective in increasing resistance to creep, the alloys in general are unsatisfactory, particularly because they tend to be too brittle at room temperature. v

"It has recently been proposed to utilise magnesiumbase alloys containing up to about 1% zirconium together with about 1 to 4% cerium, and these alloys have been found to have better creep resistance at elevated temperatures and improved properties at room temperature.

With a view to modifying properties of alloys containing zirconium and rare earth metals, I have added zinc,- and find that, in addition to facilitating the production of sand castings, this addition results in a marked improvement in creep properties at temperatures over 250 .0. However such alloys, although still possessing reasonably good resistance to creep at loads of the order of 1 ton per square inch at temperatures of 300 C. or over, are subject to an unduly high rate ofcreep in the early stages. The overall creep rate of such alloys at loads over 1 ton per square inch at temperatures over 300 C. is such as to make these alloys unsatisfactory for many applications.

I have therefore endeavoured to find an alloy possessing the following combination of properties:

1. High creep resistance upv to and above 300 C. inthe initial as well as later stages of test.

- 2; Absence of. the onset of tertiary creep up to a testing time of. at least 1000 hours.

3. Good tensile strength at normal atmospheric temperatures. I

4. Sufficient elongation at room temperatures.

5. Good corrosion resistance.

6. Good casting properties.

I have now ascertained that this combination of properties including a quite remarkably high creep resistance up to and above 300 0., is obtained with alloys containing thorium and zinc in suitable relative proportions in addition to zirconium. Alloys with satisfactory resistance to creep at temperatures of 300 C. or over can also be made by adding rare earth metals to the aforev- Claims. (01. 75-9168) 2 mentioned alloying constituents, namely, thorium, zinc and zirconium.

The zirconium content should be 0.1 to 0.9 per cent, and at least 0.1% and preferably at least 0.4 per cent should be present in the soluble condition i. e. in a condition which is readily soluble (together with the magnesium) in an aqueous solution of hydrochloric acid consisting of 30 cos., of HCl (specific gravity 1.16) to 85 cos. of water, sufficient acid being added during dissolution to maintain the initial concentration.

The proportion of thorium for the purpose of the present invention is not less than nine tenths of the proportion of the zinc and not more than ;three times the quantity of zinc. .The total quan-I- 'tity of thorium and zinc together is not greater than 10%. The quantity of thorium is also not greater than nine tenths of the zinc percentage plus 2%% i. e. if the zinc is 2% the thorium will not exceed 4.55%. In addition the thorium should lie between 1 and 6% and the zinc between. A; and 5%. Preferably the thorium percentage is not greater than 1 /2 plus nine tenths of the zinc percentage and preferably not less than 1.4 times the zinc percentage less 1.5%. Preferably also the thorium content is between 2 and 5.75% and the zinc between 0.75 and 4.75%. A lower or higher percentage of zinc does not offer the desirable high creep resistance, and a higher percentage of zinc harmfully affects other properties of the alloy, such as elongation at atmospheric temperatures.

The present invention provides alloys having a creep resistance at temperatures of the order of 300 to 320 (3., much higher than in other magnesium base alloys and in fact much higher than commonly used aluminium base alloys and this high creep resistance, which is achieved in combination with good tensile strength at normal temperatures, and other sufficiently good mechanical properties, is a remarkable and unexpected advance in this art.

The alloys of the present invention preferably contain no other alloying ingredients than those abovementioned, in particular for example, silver and copper, which if included at all should not exceed 1% in the case of silver and preferably less than 0.05%, whilst the copper should not exceed 1% and is preferably less than 0.02%.

A cast test bar made from alloys according to the present invention and cast according to British Standards'Specification No. L101, Figure 1, when heat treated at 315 ,C., for 24 hours and subjectedto creep test at 315 C., under a load of 1.5 tons will have a creep strain less than 2% and tion also provides alloys having themaximum corrosion resistance in aqueous solutions of sodium chloride.

By way of example, the following alloymam be cited:

Per cent Rare earth metals, up to 4 Baryllium, up to 0.1 Calcium, up to 0.2

Silver. up to 1 Copper, up to 1 Mercury, up to 3 Lead, up to 1 Tha-llium, up to 1 Lithium, up to 12 the magnesium content being at least 85%.

3..An alloy'as' claimed in claim 1 containing 'aisoiat least oneof the following:

.. Per cent Silver, up to 0.05 Copper, up to 0.02

Zirconium -1; 0.7v

Thorium alla1- =1 1 1e e 111e1 11 3.1 Zinc a. Y..:.. Magnesium 1 balance Cast test bar of the above composition made accordim;v to. the aforesaid. British: Standards Specification whenheat treated at 315 C., for 2a. hours hadthe following. properties. atxroom temperatures:

Elongation per cent on 2 inches Ultimate Tensile I Proof Stress .1% Strength Tons per Tons per sq.

square inch inch On thesarne alloy the percentage creep strain after 500 hours at 315 C., was 0.30 under a stress of 1.5 tons per square inch.

Other ingredients. which can be usefully tolerated in the alloys are the following;

Lithium, upto 12 The total proportion of all alloying'ingredients otherthan magnesium should not exceed 15 per cent. I

'Il-ie all-oys of the present invention are-specially useful for the ma-nufacture of partsusedin or adiac'e'nt'to engines which parts are stressed and subject to temperatures of over 250 C. in use.

1; A magnesium base alloy *consistin'g'essentially of zirconiuminamount between 0.1" and 0.9%", at least 0.1% being presentin solution in the alloy, thoriflmbetWeen-1;and-6%' andjzi'nc between-0:5 and-5%, thep'ercen-tage of thorium being between ninetenthsand three times the percentage ofzinc but not exceeding nine-tenths of "t-l' efzinc content byr-more than, 2%%'',' the thoriumjand zinc together not exceedingifle'e, the balance-being magnesium;

2. An'alloyas'claimed claim 1 containing also atleast one of the following:

4. An alloy as claimed in claim 1 containing at least one of the rare earth metals in amount between 0.1 and 0.7%.

5.,A magnesium Ibase alloy consisting of essenmany zirconium in amount between 0.1 and 0.9% at least 0.1 being in solution in the alloy, thorif um between land 6%, and zinc between 0.5 and 57%" the ercentage of 'thoriunibeing between ninetenthsand three times thepercentag'e of zincihut not'ex'ceedin'g nine-tenths of the-zinc content by more than 1 /2 nor falling short of 1.4 times the percentage of zinc by more. than 1.5 per cent, the thorium and zinc together not exceeding 10 the balance beingmagl lesium. v

6'. An alloy as. claimed in claim 5 containing also at least oneof the following:

the magnesiur'ncontentbeing at least 7: An' alloy as claimed in claim 5" containing also at least one of the-following: V

ALFREDO. JESSUP.-'

REFEnENoEscI-mn The following references are of 'rec'ord in the file of this patent: V

UNITED STATES: PATENTS Number V OTHER. REFERENCES "senat 3fi 9g749; sauerwald et al. (A. P. 0.6:, published-June'15,194'3;

Claims (2)

1. A MAGNESIUM BASE ALLOY CONSISTING ESSENTIALLY OF ZIRCONIUM IN AMOUNT BETWEEN 0.1 AND 0.9%, AT LEAST 0.1% BEING PRESENT IN SOLUTION IN THE ALLOY, THORIUM BETWEEN 1 AND 6% AND, ZINC BETWEEN 0.5 AND 5%, THE PERCENTAGE OF THORIUM BEING BETWEEN NINE-TENTHS AND THREE TIMES THE PERCENTAGE OF ZINC BUT NOT EXCEEDING NINE-TENTHS OF THE ZINC CONTENT BY MORE THAN 2 3/4%, THE THORIUM AND ZINC TOGETHER NOT EXCEEDING 10%, THE BALANCE BEING MAGNESIUM.

2. AN ALLOY AS CLAIMED IN CLAIM 1 CONTAINING ALSO AT LEAST ONE OF THE FOLLOWING: