US2124552A - Magnesium alloy - Google Patents

Description

Patented July 26, 1938 UNITED STATES MAGNESIUM ALLOY John A. Gann, Midland, Mich, assignor to The Dow Chemical Company, Midland, Mich, a corporation of Michigan No Drawing.

Application November Serial No. 112,289

3 Claims.

been used commercially. In these alloy compositions, however, it is a general rule that, when the percentage of alloying constituents has been increased sufficiently 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 of 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 definite 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 of the metals magnesium, aluminum, cadmium, tin, and

zinc.

These new polynary alloys of magnesium-aluminum-tin-zinc and magnesium-aluminum-tinzinc-cadmium 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 may vary from about 1 to 16 per cent, the tin content from about 0.5 per cent to per cent, the zinc content from about 0.5 per cent to 10 per cent, and the cadmium content from about 1 per cent to 10 per cent. The magnesium content should,

in general, be not less than approximately 80 per cent when the alloy is to be used for the production of castings and extrusions, and, in general, not less than approximately90 per cent when the alloy is to be used for the production of forgings, sheet, and plate. If the castings are to be heat treated, I normally prefer to use an alloy containing approximately 6 per cent to 10 per cent of aluminum, 2 per cent to 6 per cent of tin, and 1 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 per cent. An alloy composition within the scope of my inblow impact test. U

vention, 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 approximately proportional to their tensile strengths. Toughness values are expressed in terms of foot-pounds of energy absorbed on breaking a notched bar specimen in the single- Table 1 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 aluminum (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 11 gives similar data for another series of ternary alloys compared to my new polynary Table II Similar property improvements, particularly in regard to the toughness-hardness ratio, are liken n wise obtained with other magnesium-aluminum- Composition g g gg cadmium-tin-zinc alloys as illustrated for' example, in Table V. In this case two series of 5 alloys were prepared, namely, by the addition of j$ increasing amounts of aluminum toa magnesium Ms+ 181300 alloy containing 2 per cent of tin, and 2 per cent of Mg-l-4%Sn+4%Zn+4%Al Q. 26,300 zinc; and by the addition of increasing amounts of aluminum to a magnesium alloy containing 2 In the ples giv in T bles I a d the per cent of cadmium, 2 per cent of tin, and 2' w qu a y al a be considered as per cent of zinc, thereby increasing the hardness s been produced by the addition of a fouljth and decreasing the toughness of the alloy. The 7 metal to One of the, Parent ternary alloys, W hardness and impact-toughness values for each 15 g f g g g g z ggf 8: 2 :12 g 2%;; series of alloys were plotted against the percentage of aluminum. Impact-toughness values than the correspondmg ternary alloys Table were read from these curves corresponding to III, however, shows that the quaternary alloy is Brine hardness Values of 45 50 55 and 60 likewise distinctly superior to the three parent r ternary alloys when the alloy compositions are respectively. The data n Table Vshow that for 20 so regulated that all compositions contain the a gtven hardness t tmpact'toughness Values I same total percentage of alloying constituents. of the cadmtum'bearmg alloys are greater than the corresponding values of the cadmium-free Table III alloys 25 Composition Tensile strengghitbhlisgg. in. [01' ys Table V Impact-toughness, ft.-lb. Base Added 1m 12% 4:0 8% gg, 3

- metal addedmetal addedmetal metal Brinenhatdness M +27 Mg+2% 30 I 33 Mg+8%Sn Al 15,e00-22,20o 1s,90o-22,200 22,200 zn'+ Mg+8%Zn Al 1 1,800-20, 16, 400-13, 100 18,100 Mg+8%Sn Zn 2o,1oo-21,aoo 2o,soo-21,200 21,200 Mg+4%Sn+4%Zn Al 22,1o0 2s,30o 26,300 :5 E

The new magnesium-aluminum-tin-zinc qua- 60 ternary alloys are likewise characterized by a good ratio of toughness to hardness. This was My new polynary alloys, consisting of ma established as follows. Impast-toughness and nesmm a1uminum tin zinc magnesimm 40 hardness curves were drawn for numerous series aluminum cadmium tin zinc, may be prepared 9 tentary and polynary alloys Simllar to those by the usual methods for melting and alloying listed in Tables I through III. The hardness metals with magnesium such as addm th values corresponding to impact-toughness values g 8 of 1.5, 2.25, and 3 foot-pounds respectively were spefmve alloymg metals to t of molten mag- 45 read from these curves; The tabulated data nesium protected from o ndatlon by a cover of showed that good and very good toughness-hardfluid ness ratios were obtained in 31 per cent of the other modes of applymg the Prmclpte of my magnesium a1un inum ti alloys, in 76 per cent invention may be employed instead of those exof th magnesium-a1umjnum zinc alloys, and in plained, change being made as regards the in- 5.0" 8 per cent 'of the magnesium-tin-zinc alloys gredients and the steps herein disclosed, provided whereas using the same basis of comparison, 88 those stated by any of the following claims or per cent of my new magnesium-aluminum-tintheir equivalent be employed. tsing1 aloys showed good to very good toughness I particularly point out and distinctly claim 0 ar HESS ra 10S. as my invention:

I have likewise found that the new magnesium- 1 A magnesium-base alloy consisting of aluminum-tin-zinc alloys may be improved by the proximately 1 per cent to 16 per cent of a1um1 addition ofcadmium. This is illustrated, ior num 05 per cent to 10 per cent of tin a 0.5 example y the data m Table where gains per cent to 10 per cent of zinc, the balance being are shown in strength, hardness, and toughness. magnesium. 50

Table IV 2. A magnesium-base alloy consisting of approximately 6 per cent to 10 per cent of alumi- Composition num, 2 per cent to 6 per cent of tin, and 1 per Prioperty cent to 3 per cent of zinc, the balance being mag- 5 -Mg+4% Al+ Mg+4% Al+2% Sn+ nes1um.,. 2% Sn+2% Zn 2% +273 Cd 3. A magnesium-base alloy consisting of 8 per cent of aluminum, 2 per cent of tin, and 2 per cent gg iffiggfg ggf'f gf:. gg of zinc, the balance being magnesium; Impact toughness, ft.-lb 5. 5 c. 2 70 JOHN A. GANN.