US2420293A - Magnesium base alloys - Google Patents

Description

Patented May 13, 1947 MAGNESIUM BASE ALLOYS Adolf Beck, Gustav Sicbel, and Hugo Vosskiihler, Bitterfeld, Germany; vested in the Attorney General of the United States No Drawing. Application March 2, 1940, Serial No. 322,034. In Germany March 4, 1939 7 Claims.

This invention relates to magnesium base alloys.

The high percentage magnesium base cast a1- loys heretofore known, generally contain as alloying constituents substantially only aluminium and zinc, the aluminium content amounting to between about 4 and 10% and the zinc content up to about 3%, the zinc content being smaller as the aluminium content is increased. Depending on the particular composition of the alloy and on the type of casting process (sand, chill mould or pressure die casting) these known magnesium base cast alloys have in the as cast state, a tensile strength of from 16 to 22 kgs. per square mm, an elongation of from 3 to 12% and a yield point of from 8 to 16 kgs. per square mm. (see Werkstoffhandbuch Nichteisenmetalle, 1936, sheet K. 3).

However these known alloys have the disadvantage that they suffer from a tendency to microshrinkage on solidification. This micro-shrinkage leads to the formation of microscopic discontinuities in the structure which not only involve a certain lack of tightness of the casting against pressure of liquid or gaseous media, but which also have a notch effect and thus, on occasion, substantially impair the strength properties attainable in the case of a sound structure, particularly in highly stressed thick sections. Attempts have hitherto been made to counteract micro-shrinkage by an ample use of chill plates and other measures for the rapid cooling of such sections; such measures, however, are expensive to apply and their effect is difficult to control in practice, moreover they are frequently only partially successful.

The present invention aims at providing new magnesium base alloys which are equal and in some cases even superior to the hitherto known magnesium base cast alloys in respect of mechanical strength, whilst being much less liable to micro-shrinkage than such known alloys.

The alloys of the present invention are characterized in that they contain cerium in amounts ranging between about 0.1 and about 2% as well as zinc between about 0.5 and about 12%. Preferably, the cerium content varies between about 0.5 and about 1.5%, while the zinc content is maintained between about 4 and about 8%.

The term cerium used herein is intended to include the so-ca1led Cerium Mischmetall.

In addition to the aforementioned metals, the alloys of the present invention may contain further alloying constituents which are soluble in magnesium in the solid state in the presence of the specified amounts of the two principal alloying constituents viz. cerium and zinc. Such additional alloying constituents are especially cadmium, tin and. silver. The amount of these additional alloying constituents can be up to 10%, but preferably does not exceed 4%. The alloys of the present invention may also contain aluminium but in this connection it has been found that the presence of substantial amounts of aluminium, i. e., about 1% or more, introduces an increased tendency to micro-shrinkage which becomes exceedingly pronounced when the aluminium content exceeds 3%. Consequently the alloys of the present invention are preferably free from aluminium or if they contain aluminium as an intentional constituent, the aluminium content is preferably less than 1%.

The presence of even the smallest amounts of silicon likewise has an unfavourable effect on the properties of the alloys of the present invention, so that the silicon content of the alloys should be kept below 0.05% and preferably below 0.01%. The presence of antimony is also detrimental. On the other hand, the normal iron content of magnesium (about 0.05%), which in the case of hitherto known magnesium cast alloys was regarded as undesirably high, not only has no unfavourable eiiect in the case of the alloys of the present invention, but even appears to improve the properties of said alloys.

For the purpose of improving their resistance to corrosion, the alloys of the invention preferably also contain between about 0.3 and 0.8% of manganese.

It has further been found that the mechanical strength properties of the hereindescribed alloys can be very considerably further improved by suitable heat treatment. This heat treatment comprises heating (soaking) the alloys for several hours, preferably at the highest possible temperatures, i. e., as closely as possible below the solidus point, and, after rapid cooling (for example in the atmosphere), annealing them for a longer period than the soaking period, at lower temperatures (between about and 250 C.). For an alloy containing 0.75% of cerium and 4% of zinc, for example, heating at 515 C. for 5 hours and annealing at C. for 20 hours or longer have been found convenient. The soaking can also be dispensed with on occasion and the heat treatment restricted to the annealing, in which case, however, the aforedescribed improvement of the mechanical properties is generally substantially smaller.

in the following table a number of alloys according to the invention are given by way of example, together with their mechanical strength properties. By way of comparison the corresponding values of two magnesium base alloys between about 0.1 and about 2% of cerium, between about 0.5 and about 12% of zinc, and at least one other alloying metal capable of forming a solid solution with magnesium in the pres- (No. 1 and No. 2 in the table) are indicated, the 5 ence of cerium and zinc in a total amount not first of which contains 0.3% of manganese as exceeding about 4%, said alloy being characsole alloying constituent and the second 0.3% terized by greater freedom from micro-shrinkage of manganese and 0.5% of zinc, as the sole alloythan a magnesium base alloy of the same compoing constituents, both alloys thus being free sition but devoid of said amount of cerium. from cerium. 10, 5. A magnesium base casting alloy containing Alloy Strength properties No. State Tensile 05 Zn ca Mn fla g 112. 1%? q mmsquare mm.

0.3 011111 casting. 14.4 7.4 3.0 0.5 0.3 10.5 4.7 3.3 .25 0. 5 19. 20. 0 0. 0 .75 2. 0 20. 4 17. 0 8.1 .75 4.0 21.2 13.7 3.3 .75 0.0 20.1 8.0 8.7 1.0 2.0 10.3 12.0 7.0 1.0 0.0 22.3 11.0 5.9 1. 2. 0 17. 5 7. 0 7. 5 1.5 0.0 5 do 18.2 7.2 7.1 1.0 2.0 Sand casting heat treated.. 22. 5 10. 4 l3. 5 0.75 5.0 .5 -do 25.5 5.0 13.3 0.75 0.0 0.5 23.5 3.4 22.3 0.75 4.0 4.0 0.5 20.3 9.4 10.0

The best strength properties are usually obtained with smaller contents of cerium; an increase in the cerium content within the limits defined by the invention, however, leads to a still more complete suppression of micro-shrinkage. By suitably proportioning the content of the alloys of the present invention it is thus possible to produce alloys having particularly good strength properties or else alloys particularly free from a tendency to micro-shrinkage, the choice between the two alternatives depending substantially on the purpose for which the alloys are intended.

The alloys of the present invention are not only suitable for the production of shaped castings, but also possess good properties in the wrought state.

We claim:

1. A magnesium base casting alloy containing between about 0.5 and about 1.5% of cerium and between about 4 and about 8% of zinc, said alloy being characterized by greater freedom from micro-shrinkage than a magnesium base alloy of the same composition but devoid of said amount of cerium.

2. A magnesium base casting alloy containing between about 0.5 and about 1.5% of cerium and between about 4 and about 8% of zinc, the aluminum content of said alloy being less than about 1% and the silicon content being less than about 0.05%, said alloy being characterized by greater freedom from micro-shrinkage than a magnesium base alloy of the same composition but devoid of said amount of cerium.

3. A magnesium base casting alloy containing between about 0.1 and about 2% of cerium, between about 0.5 and about 12% of zinc, and at least one other alloying metal capable of forming a solid solution with magnesium in the presence of cerium and zinc in a total amount not exceeding about 10%, said alloy being characterized by greater freedom from micro-shrinkage than a magnesium base alloy of the same composition but devoid of said amount of cerium.

4. A magnesium base casting alloy containing between about 0.1 and about 2% of cerium, between about 0.5 and about 12% of zinc, and further at least one other alloying metal of the group consisting of cadmium, tin, and silver in a total amount not exceeding about 4%, said alloy being characterized by greater freedom from micro-shrinkage than a magnesium base alloy of the same composition but devoid of said amount of cerium,

6. A magnesium base casting alloy containing between about 0.1 and about 2% of cerium and between about 0.5 and about 12% of zinc, the balance being magnesium and not more than about 0.3 and about 0.8% of manganese and 10% of metal capable of forming a solid solution in magnesium in the presence of the cerium and zinc content of the alloy.

7. A magnesium base casting alloy containing between about 0.1 and about 1.5% of cerium and between about 4 and about 8% of zinc, the balance being magnesium and not more than about 0.3 and about 0.8% of manganese and 4% of metal capable of forming a solid solution in magnesium in the presence of the cerium and zinc content of the alloy.

ADOLF' BECK. GUSTAV SIEBEL.

HUGO vossKI'irnnR.

REFERENCES CITED The following references are of record in, the file of this patent:

UNITED STATES PATENTS Number Name Date 2,045,244 Paine June 23, 1936 2,121,292 Haughton June 21, 1938 1,936,550 Gann Nov. 21, 1933 1,558,066 Veazey Oct, 20, 1925 1,850,612 Wood Mar. 22, 1932 2,221,319 Altwicker Nov. 12, 19.40

FOREIGN PATENTS Number Country Date 810,610 France Dec. 28, 1936