US2314852A - Heat treatment of magnesium base alloys - Google Patents

Description

March 23, 1943.

A. BRANDT HEAT TRIilAEIIMEll'l QF MAGNESIUM BASE ALLOYS Filed Oct. 8, 1941 BCDEFGH 3mm: W364 m&z

Patented Mar. 23, 1943 HEAT TREATMENT OF MAGNESIUM BASE ALLOYS Alfred Brandt, Swansea, Wales, assignor, by mesne assignments, to The Anglo California National Bank of San Francisco, San Francisco, Calif., a national banking association, as trustee Application october 8, 1941, Serial No. 414,176 In Great Britain September 9, 1940 2 Claims.

This invention relates to high percentage magnesium base alloys and is particularly concerned with raising the yield point (proof stress) of the alloys by subjecting the same in the as-cast" condition to a single-step heat treatment within a range of not less than 100 C. but less than 250 C., having avoided any previous thermal treatment at higher temperatures.

It is an object of the present invention to avoid the so-called solution heat treatment at temperatures far above 250, which constitutes, with subsequent chilling, the first stage of the thermal treatment of magnesium bas alloys which has therefore been the standard practice in treating castings of this type, an annealing treatment at a lower temperature,' below 200 C., being preferably carried out as a second stage. The singlestep thermal treatment at low temperatures leaves the strength of the material substantially unaltered, and the elongation may even decrease to some extent. On the other hand, the yield point is materially increased. Uniformity of results, reduction of wastage, the lessening of fire risks, are also possible-advantages.

According to the present invention, the singlestep heat treatment between 100 C. and 250 C. is applied to magnesium base alloys containing more than 7% but less than 12% of aluminum,

' plus at least about 0.2% and less than 4% zinc,

and also containing from 0.1% to 1.0% of manganese. the total amount of alloying constituents being not'above 12%.

The following examples illustrate various indinates corresponding to yield point in tons per square inch.

Turning now to the figure of the drawing and reading from the left, the efiect of the heat treatment of magnesium base alloy castings A to H inclusive of the hereinafter appearing table is illustrated. Th top line of each of the various columns in the drawing indicates the yield point (tons per square inch, for 0.1% permanent deformation) of the heat-treated casting, the line in the same column somewhat below it indicating the yield point of the unheat-treated alloy, that is to say, the alloy in the condition resulting from casting, or in other words, the condition known as as cast" condition.

The table given below contains the percentages by weight of "the castings subject totolerance for usual impurities together with the heat treatment which they received, namelyz' Heat treatment in days at 0.

3x140 3x140 2x140 3x140 3x175 1x240 1x240 3x175 In preparing the above examples and diagrams, alloys were made up and cast into tensile test bars in accordance with the specifications of the British Air Ministry Department of Technical Development. 0.1% yield point was determined in the case of each alloy in the "as cast con-, dition, and after heat treatment at C. for 1, 2 and 3 days, after heat treatment at C. for 1, 2 and 3 days and after heat treatment at 240 C. for 1, 2 and 3 days. Duplicate tests were carried out in each case.

I claim:

1. A method for improving the yield point of cast magnesium base alloys containing more than 7% but less than 12% of aluminum, at least about 0.2% and less than 4% of zinc and from 0.1% to 1.0%.of manganese, the total amount of alloying constituents being not above 12% the balance being substantially all magnesium, which comprises subjecting such alloys in the as-cast condition to a heat treatment at a temperature within the range of 100 C. to 250 C.

2. An alloy consisting principally of magnesium and containing from '7 to 12% of aluminum, at least about 0.2% and less than 4% ofzinc and from 0.1% to 1.0% of manganese,- and the balanc substantially all magnesium, the total amount of alloying constituents not exceeding 12%, in the form of shaped castings the yield point of which has been raised without appreciable increase in strength by heat treatment in the as-cast condition at a temperature within the range of 100 C. to 250 C.

ALFRED BRANDT.

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