US2127254A - Magnesium alloy - Google Patents

Description

Patented Aug. 16,1938

UNITED STATES PATENT OFFICE mesne assignments, ment Corporation, a

to Magnesium Developcorporation of Delaware No Drawing. Original application August 7, 1935,

Serial No. 35,126. Divided and this application July 2, 1937, Serial No. 151,699

4 Claims.

This application is a divisional application of my copending Serial No. 35,126, filed August 7, 1935. The invention herein relates to wrought magnesium base alloys, and it is particularly concerned with those alloys which contain from about to per cent aluminum, 0.1 to 1 per cent manganese, 0.05 to 0.5 per cent calcium, and 0.1 to 1.5 per cent zinc.

Magnesium base alloys containing aluminum and zinc have proved to be quite satisfactory for the production of castings. Manganese is frequently added to these alloys for the purpose of improving their corrosion resistance, but it does not affect their casting quality to any substantial degree. Where attempts have been made to hot work these same alloys in the production of wrought articles, it has been found that the best workability is obtained by limiting the aluminum content to less than about 3 per cent. However, alloys containing 5 per cent or more aluminum have a higher strength and consequently are desired for many applications. Also, as the aluminum content of these alloys is increased, they become more diflicult to work, especially at elevated temperatures, because of the tendency of the billets to crack when pressed, rolled, or forged. In order to successfully fabricate the alloys containing more than 5 per cent aluminum it has been necessary to exercise rigid control over the heating and working conditions. In other words, the attainment of high strength in alloys of the foregoing type is achieved at the expense of ease in hot working.

In the production of wrought articles, the major portion of the reduction or change in shape is accomplished at an elevated temperature where the metal is much more plastic than at ordinary temperatures. As a matter of practice the deformation of the metal is performed well above the temperature at which strains would be developed of the character found in the cold worked product. In the fabrication of magnesium base alloys hot working is usually done above about 600 Fahrenheit. At this and higher temperatures the alloys are readily shaped without leaving deleterious residual strains. Although the alloy becomes suiiiciently plastic at these temperatures to be easily deformed, it may lose its cohesive quality to such an extent that cracks or incipient fractures are created under pressure of the hammer, roll, or plunger, which prevent it from being utilized in the subsequent manufacture of wrought articles. Some alloys are more prone to exhibit this behavior than others. Magnesium base alloys containing from about 5 to 10 per cent aluminum, 0.1 to l per cent manganese, 0.05 to 0.5 per cent calcium, and 0.1 to 1.5 per cent zinc belong to this group which in terms of the art are called hot short. Particular pains must therefore be taken to avoid the formation of cracks with a consequent increase in cost of production. I

My invention is directed toward overcoming the disadvantages enumerated hereinabove with respect to the hot working of magnesium-aluminum-manganese-zinc-calcium alloys. In particular, it is an object of my invention to improve the ductility of these alloys at elevated temperatures without detracting from their strength or other desirable properties. I have discovered that magnesium-aluminum-manganese-zinc-calcium alloys can be'rendered more ductile under the conditions imposed by working at high temperatures, such as have been referred to above, by the addition of a small amount of lead amounting to from 0.1 to 1 per cent of the total weight of the alloy. I have found, in addition, that this alloying constituent does not substantially change or affect other desirable properties of the base alloy, but only effects a remarkable and beneficial change in its working characteristics at elevated temperatures. Further, I have determined that the hot working properties of magnesium-aluminum-manganese zinc calcium alloys can be similarly improved by incorporating in the alloy an amount of thallium and cadmium varying in amount from 0.1 to 1 per cent of the total weight of'the alloy. My improved alloys containing the metals lead, thallium, and cadmium, individually or collectively in combination, within the amounts set forth, show a pronounced beneficial effect during hot working, which is surprising in view of the small amount of the alloying constituent employed. If used in combination, the total amount should not exceed 2 per cent. The operation of hot working oi. this type of base alloy is simply and economically expedited by the use of these improved alloys.

The operation of my invention is well exemplified by the following test which has been found tov indicate the relative capacity of different alloys for being hot worked. The test comprises heating test bars mounted in a fixture to a predetermined temperature, immediately fastening the bar and fixture to a pendulum, and causing the pendulum to swing so that a cross member of the fixture encounters a stop on the frame of the machine with the resultant breaking of the bar in tension on impact. The elongation of the broken test piece is then measured, the alloy having the greatest elongation under the impact being considered the most ductile and susceptible to hot working without exhibiting cracks. An exceptionally high correlation has been established between the results of this test and the actual behavior of alloys when rolled, extruded, pressed, or forged. The test has therefore come to be treated as a reliable guide in ascertaining the relative workability of different alloys at elevated temperatures.

The eflect of lead, thallium, and cadmium is illustrated in alloys of the composition indicated below which were extruded and heated to a temperature of 550 Fahrenheit, 600 Fahrenheit, the practicable minimum hot working temperature, 650' Fahrenheit, and 700 Fahrenheit, and. broken in tension under impact. The temperature to which the particular bars were heated and the elongation oi the broken test pieces are also shown in the table below.

cent aluminum, 0.2 to 0.0 per sent manganese, 0.05 to 0.25 per cent calcium, 0.1 to 1.3 per cent zinc, and 0.2 to 0.75 per cent or at least one oi the metals lead, thallium, and cadmium are particularly desirable in making wrought articles.

The alloy may be produced in any suitable manner. I prefer, however, to add the heavy, low melting point metals to the melt in elemental form, stirring the liquid bath suificientiy to prevent segregation or settling or the added substance.

I claim:

1. A magnesium base alloy containing from 5 to 10 per cent aluminum, 0.1 to 1 per cent manganese, 0.1 to 1.5 per cent zinc, 0.05 to 0.5 per cent calcium, and 0.1 to 1 per cent cadmium, and characterized by improved ductility and i'reedom from hot-shortness under mechanical deformation at elevated temperatures.

2. A magnesium base alloy composed of 6.5

Composition Per cent elongation in 2" at- .u Zn Mn Ca ,Pb '11 ca 550 s. 000 F. 650F. 100 F.

0.5' 0.5 0.3 27.0 22.5 10.0 as 0.5 0.3 34.0 41.1 39.1 12.5 o. a o. 0.1 30. 2 41.1 10.3 10. 0 a. s 0. a 0. a 32. 0 31.8 26. 2 11s. 1 0.5 0.5 as 35.1 40.2 36.5 22.2 o. 5 o. 5 0. a 35. a a9. a a9. a 12. 4

From the foregoing data it is at once apparent that the elongationot the basic magnesium-aluminumzinc-manganese*calcium alloy decreases rapidly above 600 Fahrenheit, whereas the alloys containing lead, thallium, or cadmium show a much lower diminution in this property with arise in temperature above 600 Fahrenheit. Furthermore, it is to be observed that the latter alloys show a better ductility at all the temperatures than does the normal product.

While magnesium base alloys composed of magnesium, irom about 5 to per cent aluminum, 0.1 to 1 per cent manganese, 0.05 to 0.5 per cent calcium, 0.1 to 1.5 per cent zinc, and 0.1 to 1 per cent 01' at least one of the group of elements lead,

thallium, and cadmium, may be satisfactorily hot worked, I have found that those alloys which are composed of magnesium, from about 6 to 9 per per cent aluminum, 0.5 per cent zinc, 0.3 per cent manganese, 0.1 per cent calcium, and 0.5 per cent cadmium, the balance being magnesium.

3. A magnesium base alloy containing from 5 to 10 per cent aluminum, 0.1 to 1 per cent manganese, 0.1 to 1.5 per cent zinc, 0.05 to 0.5 per cent calcium, and 0.1 to 1 per cent each of cadmium and thallium, and characterized by improved ductility and freedom from hot-shortnem under mechanical deformation at elevated temperatures.

4. A magnesium base alloy containing from 5 to 10 per cent aluminum, 0.1 to l per cent manganese, 0.1 to 1.5 per cent zinc, 0.05 to 0.5 per cent calcium, and 0.1 to 1 per cent each of cadmium and lead, and characterized by improved ductility and freedom from hot-shortness under mechanical deiormation at elevated temperatures.

EDWARD F. FISCHER.