US2221247A - Magnesium base alloy - Google Patents

Description

Patented Nov. 12, 1940 UNlTED STATES MAGNESIUM BASE ALLOY John C. McDonald,

Midland, Mich., assignor to The Dow Chemical Company,

Midland, Mich.,

a corporation of Michigan No Drawing. Application November 13, 1939,

Serial No.

4 Claims.

The invention relates to magnesium base alloys. It more particularly concerns alloys of this nature having a high degree of iormability, coupled with improved physical properties, such as high tensile and yield strengths.

Magnesium alloys are being widely used in structural and mechanical arts where a light weight metal is highly desirable, such as for use in making large casting forgings, and the like. However, the use of these alloys in the rolled form to make sheet metal articles requiring forming operations, such as bending, drawing, and the like, has not progressed very rapidly due to the fact that, in general, alloys of good formability, permitting relatively sharp bends to be made without the article developing external properties of a related alloy, illustrates the'improvement in yield strength, tensile strength, and ductility or formability, as represented by the per cent increase in elongation, of the new alloy over that of a closely related quaternary alloy.

Table Nominal composition in percent (magnesium remaindar) Annealed Cold rolled Yield Tensile Percent Yield Tensile Ag Ce Mn Zn strength in strength in elon ation strength in strength in Ilia/sq. in. lbs./sq. in. in 2 ches lbs./sq. in. lbs./sq. in

cracks, have inferior characteristics as regards their tensile and yield strengths.

It is accordingly the principal object of the invention to provide a magnesiumbase alloy which can be made into rolled sheet or the like, possessing a suflicient degree of ductility or formability at ordinary temperatures to be sharply bent, drawn, or otherwise shaped, while having greatly improved tensile and yield strengths.

Other objects and advantages will be apparent as the description of the invention proceeds.

My invention resides in the discovery that a magnesium base alloy composed of from about 7 0.3 to 10 per cent of silver, 0.05 to l per cent of calcium, 0.1 to 3 per cent of manganese, and from 0.1 to 10 per cent of zinc, the balance being substantially all magnesium, is endowed with atore-mentioned properties. While the properties oi good-iormability or ductility, coupled with the increased tensile and yield strengths are manifest over the entire range of the composition indicated, I have found that, in general, the preferred combination of properties, such as the most desirable ductility for forming operations, coupled with high tensile strength and greatly increased yield strength is found in those The properties listed in the above table under the section headed by the term annealed were obtained by first rolling the alloys at a temperature between about 500 to 600 F., and thereafter annealing them at various temperatures through a temperature range of from 400 to 800 F. The properties selected for the table were those of the annealed specimens which exhibited the maximum elongation. The properties listed under the section headed cold rolled were obtained by subjecting specimens of the alloys which had been hot rolled at a temperature I of from 500 to 600 F. to additional rolling in the cold state, to bring about a total reduction of from '2 to 10 per cent. The properties selected for the table were those 01 the cold rolled specimens which showed the greatest tensile and yield strengths, while having at least a l per cent elongation in 2 inches.

By a comparison of the properties set forth in the above table, it will be observed that, in general, the combined properties of my new polynary alloy are always superior to those of the related quaternary alloys. For example. it'will be noted that in the annealed state my new alloy shows improved elongation, as well as improved tensile and yield strengths over that of the related quaternary alloy. In the cold rolled state the yield and tensile strengths of the new alloy also showed a high degree of improvement. Similarly in other ranges of alloying ingredients the properties of the new alloy show improvement over those of the related alloys. The improvement in the physical properties of my new alloy over that of a related alloy is also shown by a conventional bend test, which serves to measure the formability or ductility of a specimen. In making the conventional bend test referred to above, the specimen is subjected to a 90 bend and the minimum radius of a bend which can be produced without fracture of the specimen; at room temperature is noted. The minimum radius thus obtained, expressed in terms of the thickness of the specimen being subjected to the test, serves as a measure of the ductility or formability of the specimen. An annealed specimen of mynew alloy had a ductility of 2.1 times the thickness of the specimen when subjected to the above test, While the ductility of the related silver-manganese-zinc alloy, as measured by the same test, was 5.3 times the thickness of the specimen.

While the new alloy is most useful in wrought form, such as sheets, due to its formability characteristics, it may also be suitably used in making castings, forgings, extruded forms, and the like. It is further pointed out that my new alloy is amenable to solution and precipitation heat treatments, which, accordingly, modify its properties.

The new alloy may be compounded in any of the ways known to the art, such as by adding the alloying ingredients to the molten magnesium under a suitable flux. The flux should be substantially free from magnesium chloride if the calcium content of the alloy is to be above 0.3 per cent. In those instances where an alloy is to be compounded containing less than 0.3 per cent of calcium, magnesium chloride may be present in the flux, but in this case it is usually preferable to add the calcium last and without too much stirring in order that the loss of calcium into the flux will be substantially prevented.

I claim:

1. A magnesium base alloy containing from 0.3 to 10 percent of silver, 0.05 to 1 per cent 01'. calcium, 0.1 to 3 per cent of manganese, and 0.1 to 10 per cent of zinc, the balance being magnesium.

2. A magnesium base alloy containing from 0.3

to 4 per cent of silver, 0.1 to 0.3 per cent of cal- JOHN C. MCDONALD.