US2844463A - Magnesium-base alloys - Google Patents

Description

United States Patent MAGNESIUM-BASE ALLOYS Ren Lucien, Paris, and Emile Tetart, Louvie-Juzon, France, assignors to Societe dInventions Aeronautiques et Mecaniques S. I. A. M., Fribourg, Switzerland, a corporation of Switzerland No Drawing. Application May 26, 1954 Serial No. 432,575

Claims priority, application France November 9, 1953 1 Claim. (Cl. 75-168) This invention relates to magnesium alloys.

It is well known that alloys of magnesium are being more frequently used for castings, especially aeronautical construction. Until recently, alloys of magnesium, aluminum and Zinc were the only casting alloys used in practice and they are still regularly used at the present time. They exhibit, however, a fairly marked tendency to microscopic porosity which results in a fairly considerable deterioration of mechanical characteristics in certain solid zones. This defect has practically eliminated the use of many different alloys of this type, with the exception of, for example, the alloy G. A. 9 (8% A1, 0.5% Zn) which is the least subject to this fault, and which, in addition, has the best mechanical characteristics.

With a view to obtaining alloys of magnesium which are much less subject to the occlusion of microscopic holes, alloys containing cerium have been proposed, either pure or in the form of mischmetall, and its addition has been particularly advocated to the extent of a content of approximately 0.5 to 1.5% to alloys of magnesium, zinc and manganese. Alloys containing cerium are, however, almost unusable for casting purposes in view of their high oxidizing properties, their great sensitivity to silicon content, even in very small percentages, which leads to the necessity of a high content of iron so as to counteract the bad effects of the silicon (the iron content being, furthermore, very difficult to obtain and being also had from the point of view of corrosion) and, finally, the propensity of these alloys to produce excessively large coarse crystalline formations or to possess defective mechanical characteristics.

On the other hand, the problem of the occlusion of microscopic holes can only be resolved in these alloys by a compromise since a choice must be made between very good mechanical characteristics which are, however, accompanied by micro-porosity (a large zinc content and a small content of mischmetall) or, conversely, an absence of micro-porosity accompanied, however, by bad mechanical characteristics (a low zinc content with a high content of rare earths).

Research and tests which have resulted in the present invention have made it possible to establish that the behavior of these alloys from the point of view of their oxidizability as well as their tendency to coarse crystallization may be very greatly improved and the strict conditions governing the content of silicon and of iron may be relaxed by suppressing the manganese and by the addition of aluminum and of beryllium in respective percentage contents of the order of 0.5% and 0.01%. In the case of alloys of this kind, it is no longer necessary to increase artificially the normal content of the alloy in iron, While on the other hand, the silicon may have a content of 0.15% without detrimental effects.

In this way, the elimination of the manganese and the Patented July 22, 1958 "ice presence of aluminum and beryllium in the proportions indicated above enable high iron content and low silicon contents to be dispensed with, the latter being necessary in order to obtain acceptable mechanical characteristics in the case of magnesium, manganese and cerium alloys.

The alloy of magnesium, the composition of which is given below, is provided in accordance with the invention:

Aluminum 0.5%.

Beryllium 0.01%.

Zinc 6 to 7% Mischmetall 0.5 to 1.5%.

Silicon Acceptable up to 0.15% Magnesium The remainder.

It will be noted that a proportion of silicon may be permitted up to a limiting content which is about ten times greater than that which could be tolerated in the case of previous alloys, so as to obtain acceptable mechanical characteristics.

The applicants have observed that the advantageous results obtained through the alloys considered are particularly marked when the mischmetall used is roughly in accordance with the following composition:

Cerium 47 to 50%. Lanthanum 25 to 27%. Neodymium 15 to 17%. Praseodymium, Samarium, Yttric earths Together 8 to 10%. Iron 0.2 to 0.5%. Silicon 01% maximum.

The invention also comprises a heat treatment applied to the alloys which have the compositions referred to above.

Homogenization is carried out in two stages, the first at about 338 centigrade, and the second at a temperature in the neighborhood of 460 centigrade. By this means, increase of granular structure during heat treatment is avoided. For hardening, a simple cooling in air is sufiicient. This homogenizing treatment is followed by a tempering treatment which is also carried out in two stages, the first stage for example at 140 centigrade and the second at 160 centigrade. These tempering temperatures can, however, be varied between fairly wide limits; for the first stage between and 150 centigrade and for the second stage between and 200 centigrade, depending on the results it is desired to obtain and the composition of the alloy.

What we claim is:

Magnesium alloy consisting essentially of the following: 6 to 7% of zinc 0.5 to 1.5% of mischmetall 0.5% of aluminum 0.01% of beryllium Residue: magnesium References Cited in the file of this patent UNITED STATES PATENTS 1,941,039 Luschenowsky Dec. 26, 1933 2,302,968 McDonald Nov. 24, 1942 2,420,293 Beck et al May 13, 1947 2,549,955 Jessup et a1. Apr. 24, 1951 2,569,477 Leontis Oct. 2, 1951 2,609,309 Meier Sept. 2, 1952 2,622,049 Hesse Dec. 16, 1952 FOREIGN PATENTS 693,478 Great Britain July 1, 1953 113,802 Australia Sept. 4, 1941