US1914589A - Magnesium base alloys - Google Patents

Description

a division of my copending application Se- Patented' June 20, 1933 UNITED smrizz s- PATENT OFFICE ROBERT T. WOOD, OF LAKEWOOD, OHIO, ASSIGNOR, BY MESNE ASSIGNMENTS, TO MAGNESIUM DEVELOPMENT CORPORATION, A CORPORATION OF DELAWARE MAGNESIUM BASE ALLOYS No Drawing. Original application filed May 19, 1931, Serial No. 538,607. Divided and this application filed November 4, 1932. Serial No. 641,234.

The invention relates to magnesium base alloys. Heretofore, these alloys have contained as essential alloying elements such metalsv as aluininium, copper, and cadmium. Sofar as I amaware, no one has heretofore produced or investigated alloys containing magnesium in large amount and smaller,- but effective, amounts of zinc, tin, and calcium, in which manganese is a valuable alloying element. This application is rial No. 538,607, filed May 19, 1931.

I have discovered that magnesium base alloys containing tin, zinc, calcium and manganese may be cast, rolled, forged. ex-

' truded, and similarly treated according to well known methods, provided the proper proportions of each alloying element be present as hereinafter disclosed. They are also susceptible of improvement by the ordinary heat treatments known to the art, and in addition, the physical properties, especially the yield point and hardness, of these alloys ma be substantially improved by so-called artificial aging treatment subsequent to the usual elevated temperature heat treatments. I havediscovered that useful alloys of this nature may be compounded containing from about 0.1 per cent to about 20 per cent tin, from about 0.1 per cent to about 10 per cent zinc, from about 0.05 per cent to about 2.0 per cent calcium, and from about 0.1 per cent to about 2.5 per cent manganese.

The particular composition of each constituent to be chosen depends upon the use to which the alloy is to be put. Consider ing, for instance, the constituent zinc, if the alloy be intended for casting purposes, an amount of from about 2 per cent to about 6 per cent is suitable, and I prefer to use about 4 per cent, whereas for purposes of extrusion from about 0.1 per cent to about 10 per cent of zinc maybe advantageously added to the alloy. If an alloy-for forging or rolling is desired, the, zinc is preferably present in amount not less than about 0.1 per cent and not greater than about 1.0 per cent.

The element tin may be incorporated in the alloy in amounts from about 4 per cent to about 8 per cent for casting purposes, and for forgings or for extrusion purposes in amounts from about 0.1 per cent to about 20.0 per cent, although I prefer to add tin in amounts between 4 per cent and 12 per cent.

The element calcium should, for casting My new alloys may be made up according to the usual metallurgical methods of alloying but I prefer to add the tin and manganese to the molten magnesium in'the form of an alloy of tin and manganese suitably proportioned in metal content to give the desired final ratio of tin and zinc in the al loys. The calcium may be added in the form of pure calcium. The zinc may be added either separately or as a tin-zinc rich alloy. The magnesium, tin, zinc, calcium, and manganese from which the alloys are made may or may not contain impurities, depending upon the purity of the metal available, but in any event small'amounts of impurities even up to about 1 per cent may be present in the alloys without seriously affecting their favorable mechanical properties. Such alloys as are herein disclosed also have a high resistance to corrosion in comparison with magnesium base alloys hitherto commercially available.-

As an illustration of the increase in yield point to which alloys within the scope of my invention are inherently susceptible, I have made up an alloy containing about 5 per cent tin, about 3 per cent zinc, about 0.73 per cent manganese, and about 0.25 per cent calcium and cast test specimens in sand molds. After casting, the yield point was 8,800 pounds per square inch, the tensile strength23,900 pounds per square inch, and the Brinell hardness 44. After a solution treatment of. 24 hours at 500 centigrade followed by an aging treatment of 24 hours at 150 centigrade, the yield point was 18,200 pounds per square inch, the tensile strength 31,900 pounds per square inch, and the Brinell hardness 56.

An increase in yield point similarly phenomenal in nature, although numerically not so great, is observable if the alloys be artificially aged after casting and without preliminary heat treatment at an elevated temperature. For instance, a sand cast 51- loy containing 5.4 per cent tin, 4.55 per cent zinc, 0.72 per cent manganese, and 0.25 per cent calcium in the as-cast condition had a yield point of 9,910 pounds per square inch and a Brinell hardness of 44, and after an artificial aging of 24 hours at 150 centigrade, it had a yield point of 14,550 pounds per square inch and a hardness of 57.

In the worked condition, alloys within the scope of this invention have exceptionally good physical properties. For instance, an extruded magnesium base alloy containing about 4 per cent tin, 3 per cent zinc, 0.2 per cent calcium, and 2.5 per cent manganese had a yield point of 26,000 pounds per square inch, a tensile strength of 46,000 pounds per square inch, and an elongation of 13.5 per cent in 2 inches. Similarly, an extruded magnesium base alloy containing about 8 per cent tin, 3 per cent zinc, 0.2 per cent calcium, and 1 per cent manganese had a yield point of about 27,300 pounds per square inch, a tensile strength of about 45,000 pounds per square inch, an elongation of 10 per cent in 2 inches, and a Brinell hardness of 66.

The heat treatment which I have found especially suited to these alloys consists in a preliminary treatment for a number of hours, preferably from 4 to 16, at about 450 centigrade to 560 centigrade followed by an artificial aging for a number of hours, preferably from about 4 to 24, below 200 centigrade and preferably between about 150 centigrade to 200 centigrade. Increase in aging time usually results in increase in yield point and hardness.

In the specification and the appended claims, the term magnesium base alloy" denotes an alloy containing more than 50 per cent magnesium, which metal may be either of high purity or may contain the usual impurities found in commercial magnesium.

I claim:

1. An alloy consisting of about 0.1 to 1.

, per cent of tin, about 0.1 to about 2.5 per cent of manganese, about 0.1 to 10 per cent of zinc, and about 0.05 to about 2 per cent of calcium, the balance being substantially magnesium.

3. An alloy consisting of about 0.1 to 20 per cent of tin, about 0.1 to 10 percent of zinc, about 0.1 to 2.5 per cent of manganese, and about 0.05 to 2 per cent of calcium, the balance being substantially magnesium, characterized by high hardness and yield point and having an internal structure produced by a heat treatment of 4 to 16 hours at 450 centigrade to 560 centigrade followed by further aging treatment at a temperature less than 200 centigrade.

In testimony whereof I hereto aifix my signature.

ROBERT T. \VOOD.

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