US2224151A - Magnesium alloys - Google Patents

Description

, Patented Dec. 10, 1940 UNITED STATES PATENT OFFICE I 2,224,151 MAGNESIUM ALLOYS No Drawing. Application February 9, 1938, Se-

rial No. 189,645. In France February 16, 1937 4 Claims.

It is a well known disadvantage of magnesium base alloys that they are liable to progressive oxidation when in the molten state and that they are also subject to superficial oxidation when in 5 the solid state, particularly at relatively high temperatures such as for instance higher than 300 C.

In order to reduce the liability of magnesium base alloys to oxidation it has been proposed to incorporate small quantities of calcium in the alloys. It has also been suggested that the addition of small quantities of beryllium to'such alloys reduces their liability to oxidation, and it is true that the effect of an addition of beryllium in respect of this liability to oxidation is far more pronounced than that of corresponding amounts of calcium. On the other hand it'has been observed that the incorporation of beryllium in magnesium. or magnesium base alloys imparts to the metal on solidification an extremely coarsegrain texture as compared with the corresponding metals in which beryllium is absent. Owing tothis coarse-grain texture, the alloys containing beryllium have low mechanical strength properties and particularly fatigue strength; moreover, when a thermal treatment of the metal or alloy is required, then the coarse-grain texture necessitates a much longer duration of such treatment than otherwise would be required.

It is an object of the present invention to provide magnesium base alloys containing beryllium in which the favourable known effects of beryllium as an inhibitor of oxidation are preserved, while at the same time avoiding the tendency to coarse-grain crystallisation otherwise observable in magnesium alloys containing beryllium.

I have found that the presence of zirconium in magnesium base alloys containing beryllium has the effect of imparting thereto, on solidification, a fine-grain structure without in any way impairing the resistance to oxidation due to the presence of the beryllium. At the same time, the joint presence of zirconium in the alloy avoids the undesirable reduction in mechanical properties imparted thereto by the presence of the beryllium, the mechanical strength properties being at least equal to those of the original metal or alloy containing neither beryllium nor. zirconium.

By way of example, beryllium can be present in the metal or alloys in amounts lying between 0.005 and 0.5% while zirconium is present in amounts lying between 0.005 and 0.5%.

It has been found that a content of 0.025% of beryllium imparts to the alloy 8. sufllcient resistance to oxidation for all practical purposes, while a zirconium content of 0.05% is sumcient to counteract the disadvantages caused by the presence of that amount of beryllium in the alloy.

Based on the foregoing observations, the present invention provides a magnesium base alloy containing both beryllium and zirconium, preferably each in an amount lying between 0.005 and 0.5%.

Theinvention also provides a process of grainrefining magnesium base alloys containing beryllium, which consists in adding zirconium to said alloys.

The zirconium can be added either in making 15 up the alloys or when remelting ingots or scrap.

The zirconium may be introduced in any desired manner, for example in the form pro-alloys, or in the form of salts of zirconium which are adapted to be reduced to metal in contact with the molten magnesium or magnesium base alloys.

The alloys of the present invention can even be melted without use .of a flux. Due to the decreased liability to oxidation of the molten alloy, losses by burning arereduced to a minimum and when no flux is used, salt inclusions in the metal, and therefore with their attendant risks of corrosion are impossible.

A further advantage arising out of the invention is that when subjecting the alloys to heat treatment, the duration of the latter is the same as that for the same alloy, containing neither beryllium nor zirconium. In addition the parts subjected to the heat treatment do not become oxidised and retain their original lustre.

What I claim is: l

1. A magnesium base alloy containing between about 0.005% and 0.5% beryllium and between about 0.005% and 0.5% zirconium characterized by a refined grain structure and by mechanical properties at least equal to those of the same alloy without beryllium.

2. A magnesium base alloy containing about 0.025% beryllium and about 0.05% zirconium characterized by a refined grain structure and by mechanical properties at least equal to those of the same alloy without beryllium.

3. A magnesium base alloy containing between about 0.005% and 0.5% beryllium and. between about 0.005% and 0.5% zirconium, the balance I being substantially all magnesium.

4. A magnesium base alloy containing about 0.025% beryllium and about 0.05 zirconium, the balance being substantially all magnesium. Y

GASTON GAUTHIER.