US2204568A - Magnesium alloy - Google Patents

Description

Patented June 18, 1940 MAGNESIUM ALLOY Arthur Burkhardt, Berlin-Lichterfelde, and Richard Knabe, Berlin-Zehlendorf, Germany, assignors to Georg Von Giesches Erben,

Breslau, Germany, a No Drawing.

corporation of Germany Application September 3, 1938,

Serial No. 228,323. In Germany September 21,

3 Claims.

Our invention relates to magnesium alloys, and more particularly to alloys of the class containing aluminium and bismuth.

It is an object of our invention to improve a magnesium alloy of the class aforesaid, with a view to increasing its strength, without deteriorating its resistance to corrosion.

Magnesium alloys as known heretofore and having satisfactory resistance to corrosion, are not strong, their strength being not much in excess of 30 kilogrammes per square millimeter. It is true that the strength can be increased to about 38 kgnlsq. mm. by suitable heat treatment but this is at the expense of corrosion resistance; ,The corrosion resistance of magnesium alloys is poor per se, and by the segregations which occur during the heat treatment, it is deteriorated to such an extent that the range of usefulness of such comparatively strong alloys is very'limited. Nor does the addition of manganese-which generally increases the resistance to corrosion-exert any favorable influence in the case of the alloys in consideration.

However, it has been found that the resistance to corrosion is not deteriorated if strength-increasing alloying elements are added in such quantities that such elements prevent the formation of a second phase. In the single-phase alloys thus produced the heterogenous inclusions which act as local elements and are the cause of poor corrosion resistance insecond-phase alloys of high strength, are absent. When such a single-phase alloy is heat treated for increasing its strength, segregation does not occur at the grain boundaries but, in uniform distribution, within the crystals themselves, so that the corresion resistance is not deteriorated.

Starting with these considerations, we have made the surprising discovery that magnesium alloys of the class referred to in which the content of aluminium is 8 to 14%, and the content of bismuth is 2 to 4%, possess very high strength in heat treated condition.

The remainder of the alloys may be substantially allmagne'sium. The phrase substantially all magnesium is intended to include magnesium and magnesium with the usual impurities in technical magnesium, and minor amounts of alloying elements, provided that the said constituents are present only in such percentages as not to overstep the limit of solid solubility in the mixed crystal. ents are 0.1 to 1%.

The usual rates of such constitu- The usual alloying elements are, for instance, calcium which is added for improving the castability of the alloys; manganese for increasing their resistance to corrosion; or'at least one metal of the iron group, or silicon, for improving the strength of the alloys under high temperature conditions, and for increasing their yield point.

Examples of suitable alloys-according to our invention will appear from the following table.

Alloy No. 132 1? gfi gg" he a t ii e t ed, Elfigga percent p c kg/sq. mm. percent It is understood that in all cases the remainder is substantially all magnesium.

The alloys Nos. 2 and 3 are particularly good.

We claim:

nesium.

3. A magnesium alloy containing from 8 to 14 per cent aluminium, 2.5 to 4 per cent bismuth, the remainder substantially all magnesium.

ARTHUR BURKHARDT. RICHARD KNABE.