US2178580A - Magnesium alloy - Google Patents

Description

Patented Nov. 7, 1939 v UNITED STATES PATENT OFFICE MAGNESIULI ALLOY John A. Gann, Midland, Mich assignor to The Dow Chemical Company, Midland, Mich, a corporation of Michigan No Drawing. Original application November 23,

1936, Serial No. 112,288. Divided and this application August 7, 1939, Serial No. 288,770

3 Claims. (Cl. 75-168) This invention relates to magnesium alloys and elongation and toughness. The magnesium alloy particularly to those containing magnesium in containing 8 per cent of silver, for example, had excess of approximately 80 per cent. a Brinell hardness value of 45 and the mag It is well known that the addition of certain nesium alloy containing 12 per cent of silver had metals to magnesium results in the production of a Brinell hardness value of 51. alloys possessing good strength characteristics, Magnesium-silver alloys, particularly those con- 1 while the addition of other metals results in the taining approximately 4 per cent or more of silproduction of alloys possessing good corrosion rever, are amenable to heat treatment. A solusistance. One of the major problems of the magtionheat treatment of 18 hours at 770 F. in

m nesium industry is the preparation of an alloy creased the tensile strength of the magnesium m in which both objectives are obtained at the alloy containing 4 per cent of silver from 22,300 same time. i a pounds per square inch to 24,900 pounds per Accordingly, the object of the present invensquare inch, and increased the percentage elongation is to prepare magnesium alloys which have tion from 10.0 per cent to 11.5 per cent without 35 improved physical properties and corrosion reappreciably affecting other properties. "A subsistance. Other objects and advantages will apsequent precipitation heat treatment of 48 hours pear as the description proceeds. at 350 F. produced a small increase in the ten- My invention is based on the discovery that sile strength. Precipitation heat treatment, howhighly desirable and useful alloys can be preever, produced marked property improvements,

20 pared by the addition of silver to magnesium and particularly in tensile strength, yield strength, 20 magnesium alloys, and that these alloys possess and hardness in alloys containing higher pergood strength characteristics, combined with good centages of silver. A solution of heat treatment corrosion resistance. or 18 hours at 770 F. followed by a precipitation I have discovered that the strength characheat treatment of 48 hours at 350 lit, for exteristics of magnesium may be improved to a ample, increased the Brinell hardness of the niagg5 very marked degree by the addition of suitable nesiurn alloy containing'8 per cent of silver from amounts of silver. The tensile strength of cast 45.0 to 55.5 and the Brinell hardness value of 1 pure magnesium, for example, was found to be the magnesium alloy containing 12 per cent of 14,000 pounds per square inch, while that of a silver from 51.0 to 65.5. Although beneficial 3o magnesium alloy containing 2 per cent of silver pr perty m rov m n s a tain d i alloys nso was 21,100 pounds "per square inch and that of taining approximately t0 1 pe n of i a magnesium alloy containing 4 per cent of silver 7 ver, I normally prefer to use from 0.5 to 8 per was 22,300 pounds per square inch. The yi ld cent of silver, except in those cases where maxistrength of cast magnesium was 2,500 pounds per mum properties in the heat treated condition are 5 square inch, while the yield strengths of the 'magq i n h n p f to use alloys 6011- as nesium alloys containing 2 per cent of silver taming approxim tely 4 p r cent to 8 per cent and 1 per cent of silver were 4,100 poundsper of silver. Alloys with low percentages of silver square inch and 5,100 pounds per square inch are better adapted for plastic deformation oprespectively. The addition of'2 per cent 'and s erations, while alloys with higher pe nt of 40 per cent of silver to pure magnesium raised the ilv r are et er s i ed f r the rod f no percentage elongation of the cast metal from castings- 8.0 per cent up to 10.5 per cent and 10.0 per cent Furthermore, I have discovered that the addi- 1". respectively. The toughnes of the magnesium was time of silver to commercial magnesium is benelikewise improved by the addition of silver, The ficial from the standpoint of corrosion resistance.

single blow impact value for pure magnesium This may be illustrated by alternate immersion 45.5 was 9.0 foot pounds, while the corresponding val corrosion tests conducted in a 3 per cent salt ues for the magnesium alloys containing 2 per solution. At the end of 24 hours, pure magnesium cent of silver and 4 per cent of silver were 12.6 had lost weight at the rate of 65.8 mg/cm /day, and 11.5 foot pounds respectively. The Brinell while the magnesium alloys containing 2 -per cent hardness values of these same two alloys were of silve and 4 D cent of Silver 108?; y .2 50 4 (34 and 37 respectively as compared with 33 for and 17.3 mg/cm /day respectively. in another i pure magnesium. As the percentage of silver in test the addition of 1 per cent of silver produced the alloy is increased, still greater improvements a 30 per cent decrease in the corrosion rate of are obtained in the yield strength and hardness, magnesium.

55 with a proportional decrease in the percentage 1 have also discovered that the beneficial elffects of silver are retained when at least one of the metals aluminum, manganese, zinc is added to magnesium-silver alloys, or; in other words, when silver is added to an alloy consisting of magnesium with at least one of the metals aluminum, manganese, zinc. In such alloys, the percentage of silver may vary from about 0.3'per cent to 12 per cent, the percentage of aluminum may vary from about 0.5 per cent to 12 per cent, the percentage of zinc may vary from about 0.5 per cent to 8 per cent, and the percentage of manganese may vary from about 0.1 per cent to 2 per cent (0.1 per cent to 0.5 per cent in alloys likewise containing aluminum), but the total percentage of added metals should not exceed approximately 20 per cent. The absolute percentage of 'each metal is dependent upon the use for which the alloy is intended 'and upon thepercentages of the other alloying ingredients. For plastic deformation processes, I normally prefer from 0.5 per cent to 4 per cent of silver, from 0.5 per cent to 6 per cent of aluminum, from 0.2

per cent to 0.8 per cent of manganese, and from 0.5 per cent to 2.0 per cent of zinc, with a maximum of approximately 8 per cent of added metals. For castings, Tnormally prefer from 0.5 per cent to 8 per cent of silver, from 5 per cent to 10 per cent of aluminum, from 0.1 per cent to 0.4 per cent of manganese, and from 1 per cent to 4 per cent of zinc, the percentage of total added ingredients varying from approximately 8 per cent to 12 per cent.

The following examples'serve to illustrate the beneficial effect of silver in this class of magnesium alloys as expressed by improvements in physical-nrechanical properties. For example, the ternary magnesium alloy containing 2 per cent of silver and 0.2 per cent of manganese had a tensile strength of 23,000 pounds per square inch as compared with 18,000 pounds per square inch for the binary magnesium alloy containing 0.2 per cent of manganese and 21,100 pounds per square inch for the binary magnesium alloy containing 2 per cent of silver. The yield strength of this ternary magnesium-silver-manganese alloy was 4,400 pounds per square inch as compared with 3,000 pounds per square inch for the binary magnesium alloy containing 0.2 per centof manganese and 4,100 pounds per square inch for the binary magnesium alloy containing 2 per cent of silver.

The addition of silver to magnesium-aluminum and to magnesium-aluminum-manganese alloys has been found to be particularly beneficial when the alloys are used for the production of heat treated castings. Under such conditions, comparable physical property improvements are obtained in alloys with and without manganese, but otherwise of similar composition, although the presence of manganese is desirable when the alloy is used for extrusion purposes. The addition of 2 per cent of silver, for example, increased the tensile strength of a solution heat treated magnesium alloy containing and 0.2 per cent of manganese'from 34,000 pounds per square inch to 36,000'pounds per square inch and the yield strength of this same alloy from 11,000 pounds per square inch to 12,000 pounds per square inch; Maximum improvement due to the presence of silver in alloys containing aluminum and manganese occurs in the aged or precipitation heat treated alloys, and here the effect is particularly pronounced in the yield strength and hardness values. For example, the addition 8 per. cent of aluminum 'mg/cm /day. In another silver to this same magnesium of 2 per cent of aluminum and 0.2

alloy containing 8 per cent of per cent of manganese increased the yield strength from 13,000 pounds per square inch to 18,000' pounds per square inch and the Brinell hardness from 58 to 64. W

The magnesium-silver-zinc and magnesium-silver-manganese-zinc alloys are satisfactory for the production of wrought shapes. While both alloys can be extruded readily, the former is better for rolling and forging operations, since the annealingtemperature generally employed in such operations/closely corresponds to the temperature at which precipitation of manganese occurs, and this precipitated manganese lowers the ductility and workability of the alloy. Magnesium -silver-zinc alloys, suitable for rolling, contain approximately 0.5' per cent to 3 per cent of silver and 0.5 per cent to 1 per cent of zinc, the balance being magnesium. Magnesium-silver-zinc alloys, suitable for extrusion, contain approximately 0.5 per cent to 6 per cent of silver and 0.5 per cent to 5 per cent of zinc, the balance being magnesium. Where ease of subsequent deformation is not required, as, for example, in extruded sections, I normally prefer to use magnesium-silver-manganese-zinc alloys containing 0.5 per cent to 5 per cent of silver,'0.1 per cent to 0.6 per cent of manganese, and 0.5 per cent to 6 per cent of zinc. The properties of such alloys, particularly those containing more than approximately 3 percent of silver and 2 per cent of zinc, may be further improved by heat treatment.

Although the magnesium-silver-zinc alloys may be used for the production of castings, I generally prefer to use, for such purposes, alloys containing silver, aluminum, and zinc, or silver, aluminum, zinc, and manganese.

Manganese is soluble in thistype of alloy to the extent of a few tenths of a per cent, and in suchamounts has no appreciable effect on physical property improvement, although it does improve the corrosion resistance of the alloy. The choice between the alloy with or without manganese, but otherwise of similar composition, depends largely on the use for which the product is intended. A good composition, selected from the more corrosion resistant type of alloy, contains 2 per cent of silver, 8 per cent ofaluminum, 0.2 per cent of manganese, and 3 per cent of zinc. This alloy, in the solution heat'treated condition, has a tensile strength of 27,200 pounds per square inch, 9. yield strength of 13,000 pounds per square inch, 4 per cent elongation, a Brinell hardness value of 53, and a single-blow impact value of 9.7 foot pounds. In the solution-precipitation heat treatedgcondition, this same alloy composition has the following properties,--tensile strength 31,000 pounds per square inch, yield strength 21,000'pounds per square inch, 0.5 per cent elongation, "72 Brineli hardness, anda singleblow impact value of 2.5 foot pounds.

I have likewise discovered that the corrosion resistance of the magnesium-silver alloys may be improved very materially by the addition of vat least one of the metals aluminum, manganese, zinc. For example, theloss in weight in a magnesium alloy containing 2 per cent of silver when tested in 3 per cent salt solution was 51.2 mg/cm /day, whereas the addition of 0.2 per cent of manganese reduced this corrosion rate to 4.9 instance, the addition of 0.9 per cent of manganese to a binary magnesium alloy containing 1 per cent of silver re duced the corrosion rate from approximately mg/cm /day to 1.7 mg/cm /day. In a similar fashion, the addition of 8 per cent of aluminum plus 0.2 per cent of manganese to a binary magnesium alloy containing 2 per cent of silver reduced the corrosion rate from 51.2 mg/cm /day to 1.2 mg/cm /day, while the addition of 8 per cent of aluminum plus 0.2 per cent of manganese plus 3 per cent of zinc to the binary alloy containing 2 per cent of silver reduced the corrosion rate to 0.6 mg/cm /day.

The above described alloys may be prepared by the well known methods of alloying metals with magnesium, such as adding the respective alloying ingredients to a bath of molten metal protected from oxidation by a cover of a fluid flux. The various alloying ingredients may be added singly or simultaneously, and are usually added as pure metals, except in those compositions containing both aluminum and manganese, in which case these two metals are preferably added in the form of a -10 aluminum-manganese hardener.

This is a division of my co-pending application Serial No. 112,288 filed November 23, 1936.

Other modes of applying the principle of my invention may be employed instead of those eX- plained, 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 comprising from 0.3 to 12 per cent of silver, from 0.1 to 2 per cent of manganese and from 0.5 to 8 per cent of zinc, the balance being magnesium.

2. A magnesium base alloy comprising from 0.5 to 5 per cent of silver, from 0.1 to 0.6 per cent of manganese and from 0.5 to 6 per cent of zinc, the balance being magnesium.

3. A magnesium base alloy comprising from 2 to 5 per cent of silver, from 0.1 to 0.6 per cent of manganese and from 1 to 4 per cent of zinc, the balance being magnesium.

JOHN A. GANN.