US2124563A - Magnesium alloy - Google Patents

Description

Patented m 2e, ass I ones a John A, G, Welland, Mich, asslgnor to The poration oi chigan t. Mind, Mich, a cor No Draw. application November 23,

1936,8c Ne. 1312,239. Divided and this apl lication April 14,1933, s i-ice) The present invention relates to improved light weight alloys in which magnesium is the predominant constituent.

The binary and ternary alloys of magnesium with the metals aluminum, cadmium, tin, and zinc are known. Many of their properties have been investigated and some of these alloys have been used commercially. In these alloy compositions, however, it is a general rule that, when the percentage of alloying constituents has been increased sumcientl'y to give adequate hardness, the brittleness of the alloy is unduly increased, or, in other words, the toughness of the alloy (as expressed by shock or impact resistance) is unduly decreased, thereby impairing the usefulness of this class of material.

The principal object oi this invention is the production of magnesium alloys having improved combinations of properties, and more specifically, the production of magnesium alloys having a good strength-weight ratio and a good toughness hardness ratio. Other objects and advantages will appear as the description proceeds.

This invention is based on the discovery that the above cited objectives may be obtained by simultaneously combining all of the metals magnesium, aluminum, tin, and zinc in cite. proportions to form the new quaternary alloy product consisting of magnesium, aluminum, tin, and zinc, and that this new alloy may be improved by the addition of cadmium, thereby giving as a new product a quinary alloy consisting oi the metals magnesium, aluminum, cedmium,tin, and zinc.

These new polynary alloys of magnesium-aluminum-tin-zinc andmagnesium-alumlnum-tih-zinccadmium have very good properties in the form of castings. Moreover, such alloys can be heat treated and/or readily worked, as by rolling, forging, or extrusion, to form articles having still better properties. The aluminum content mayv vary the alloy is to be used for the production of for:-

ings, sheet, and plate. It the castings are to he heat treated, I normally prefer to use an alloy contag approximately 6 per cent to it per cent of aluminum, 2 per cent to 6 per cent of tin, and l per cent to 3 per cent of zinc. When cadmium is used in this alloy, it should normally be added in amounts of 1 per cent to 5 percent. An alloy composition within the scope of my invention, which is satisfactory for the production of sheet, consists of approximately 2 per cent of aluminum, 1 per cent of tin, 0.75 per cent of zinc, 1 per cent of cadmium, the balance being magnesium.

Examples of the new polynary alloys are given in the accompanying tables which show their.

properties as determined on sand cast test specimens, with the properties of the parent ternary alloys given for comparison. in these examples, the parent ternary alloys were produced by the addition of increasing amounts of aluminum to magnesium-tin alloys, by the addition of increasing amounts of aluminum to magnesiumzinc alloys, and by the addition of increasing amounts of zinc to magnesium-tin alloys, while the new polynary alloys were obtained by adding increasing percentages of aluminum to magnesium-tin-zinc alloys or to magnesium-tin-zinccadmium alloys. Since the specific gravity of these alloys is approximately constant within the composition range under consideration, the strength-weight ratios of these alloys are approxi-, mately proportional to their tensile strengths. Toughness values are expressed in terms of footpounds of energy absorbed on breaking a notched bar specimen in the single-blow impact test.

Table I gives the tensile strength data for the new polynary alloys consisting of magnesium, 2

' per cent of tin, 2 per cent of zinc, plus increasing percentages of aluminum, compared with its parent ternary alloys. The first column of tensile strength data gives the range of values obtained by adding aluminum (or zinc) in amounts varying from. 1 per cent to 12 per cent. The second column of tensile strength data gives the corresponding values obtained by adding aluminumv (or zinc) 'over the narrower range of from 4 to 8 per cent. The third column of the tensile strength data gives the values for the alloys containing 2 per cent of aluminum (or of zinc) Table I! gives similar data for another series of ternary alloys compared to my new polynary alloy.

Table I I Tensile strength, lb./sq. in. for alloys Composition eontammvg Added 1 to 127 added 4 to 8'7 added Base metal metal metal metal Al 16, 300-22, 19, 500-22, 700 22, 300 Al 16, 300-24, 500 22, 300-23, 400 23, 100 Zn 211,900-25, zoo 23,00025,200 24,000

Mg+2%Sn+2%Zn Al 23, 700-27, 500 26,900-27, 500 25, 700

Table II Tensile Composition strength, lh./sq. in.

Mg-H% SIM-4% Al 21.600 Mg+i7 Zn-l-47 .u 23,600 Ms+4 e W 72 1 18.300

Mg+4% Sn+4% Zn+4% AI 1 25, 300

In' the examples given in Tables I and II, the new quaternary alloy can be considered as having been produced by the addition 01' a fourth metal to one of the parent ternary alloys, with the resuit that the new alloy contains a somewhat greater total percentage of added metals than the corresponding ternary alloys. Table 111, however, shows that the quaternary alloy is likewise distinctly superior to the three parent ternary alloys when. the alloy compositions are so regulated that all compositions contain the same total percentage 01' alloying constituents.

The new magnesium-aluminum-tin-zinc quaternary alloys are likewise characterized by a good ratio of toughness to hardness. This was established as follows: Impact-toughness and hardness curves were drawn for numerous series of ternary and polynary alloys similar to those listed in ables I through III. The hardness values corr sponding to impact-toughness values or 1.5, 2.25,'and 3 loot-pounds respectively were read lrom these curves. The tabulated data showed that good and very good toughness-hardness ratios were obtained in 31 percent of the magnesium-aluminum-tin alloys, in 76 per cent or the magnesium-alumin'um-zinc alloys, and in 8 per cent of the magnesium-tin-zinc alloys, whereas using the same basis of comparison, 88 per cent of my new magnesium-aluminum-tinzinc alloys showed good to very good toughness to hardness ratios.

I have likewise found that the new magnesiumaluminum-tin-zinc alloys may be improved by the addition of cadmium. This is illustrated, for example, by the data in Table IV, where gains are shown in strength, hardness, and toughness.

Similar property improvements, particularly in regard to the toughness-hardness ratio, are likewise obtained with other magnesium-aluminum cadmium-tin-zinc alloys as illustrated, for example, in Table V. In this case two series of alloys were prepared, namely, by the addition of increasing amounts of aluminum to a magnesium alloy containing2 per cent of tin, and 2 percent of zinc; and by the addition of increasing amounts of aluminum to a magnesium alloy containing 2 per cent of cadmium, 2 per cent of tin, and 2 per cent of zinc, thereby increasing the hardness and decreasing the toughness of the alloy. The hardness and impact-toughness values for each series of alloys were plotted against the percentage of aluminum. Impact-toughness values were read from these curves correspondingto Brinell hardness values of 45, 50, 55, and 60 respectively. The data in Table V show that for a given hardness, the impact-toughnessvalues of the oadmium-bearing alloys are greater than the corresponding values of the cadmium-free alloys.

My new pplynary alloys, consisting of masnesium-aluminum-tin-zinc and magnesium-aluminum-cadmium-tin-zinc, may be prepared by the usual methods for melting and alloying metals with magnesium, such as adding the respective alloying metals to a bath of molten magnesium protected from oxidation by a cover of fluid flux. This application is a division of my copending application, Serial No. 112,289, filed November 23, 1936.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the ingredients and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

I particularly point out and distinctly claim as my invention: 1. A magnesium-base alloy consisting of approximately 1 per cent to 16 per cent of aluminum, 0.5 per cent to 10 per cent of tin, 0.5 per cent to 10 per cent of zinc, and 1 per cent to 10 per cent or cadmium, the balance being magnesium.

2. A magnesium-base alloy consisting 0! approximately 6 per cent to 10 percent of aluminum, 2'per cent to 6 per cent of tin. 1 per cent to 3 per cent of zinc, and 1 per cent to 5 per cent of cadmium, the balance being magnesium.

3. A magnesium-base alloy consisting of approximately 2 per cent of aluminum, 1 per cent of tin, 0.75 per cent of zinc, and 1 per cent of cadmium, the balance being magnesium.