US2178582A - Magnesium alloy - Google Patents

Description

otented Nov. 7, i939 MAGNESIUM Annoy John A. Gama, Midland, Mich, asslgnor to The Dow Chemical Company, Midland, Mich, a corporation of Michigan No Drawing.

Original application November 23,

1930, Serial No. 112,288. mivided and this apinvention relates to ma particularly to those containing magnesi in excess of approximately 80 per cent.

it is well known that the addition of certain metals to magnesium results in the production oi alloys possessing good strength characteristics, while the addition of other metals results in the production of alloys possessing good corrosion resistance. One of the major problems of the magnesi industry is the preparation of an alloy'in which both objectives are obtained at the same time.

Accordingly, the obiectoi the present inve tion is to prepare magnesium alloys which have improved physical properties and corrosion resistance. Other objects and advantages will appear as the description proceeds.

My invention is hased'on the discovery that highly desirable and useful alloys can he prepared by the addition of silver to magnesium and magnesium alloys, and that these alloys possess good strength characteristics, combined with good corrosion resistance.

I have discovered that the strength character istics of magnesium may be proved to a very 14,000 pounds per square inch,-vvhile that of a magnesium alloy containing 2 per cent of silver was 21,100 pounds per square inch and that of a magnesium alloy containing 4 per cent of silver was 22,300 pounds mi square inch. The yield strength of cast magnesium was 2,500 pounds per square inch, while the yield strengths of the magnesi alloys containing 2 per cent of silver and t per cmt of silver were 4,100 pounds per square inch and 5,100 pounds per square inch respectively. The addition of 2 per cent and 4 mr cent of silver to pure magnesium raised the percentage elongation oi the cast metal from 8.0 per cent up to 10.5 per cent and 10.0 per cent respectively. The toughness of the magnesl was likewise improved by the addition oi silver. ihe single blow impact value for pure magnesi was 0.0 foot pounds, while the correspong values for the magnesi alloys containing 2 per cent oi silver ands per cent oi silver were 12.0 and H5 foot pounds respectively. i he ldrinell hardness values of these sametwo alloys were 34 and 37 respectively as compared with 33 tor pure I magnesium. As the percentage of silver in the alloy is increased, still greater improvements are obtained in the yield strength and hardness, with a proportional decrease in the percentage eloplicntion August 7, i030, Serial No. 288,772 3 @laims. (@l. id-108) E ,1: alloys and tion and toughness. The magnesium alloy containing per cent of silver, for example, had a Brinell hardness value of 45 and the magnesiumalloy containing 12 per cent of silver had a Brlnell hardness value of 51.

Magnesium-silver alloys, particularly those containing approximately 4 per cent or more of silver, are amenable to heat treatment. A solution heat treatment of 18 hours at 770 F. increased the tensile strength of the magnesium alloy containing t per cent of silver from 22,300 pounds per square inch to 24,900 pounds per square inch, and increased the percentage elongation from l0.0 per cent to 11.5 per cent without appreciably afiecting other properties. A-su'bsequent precipitation heattreatment of 48 hours at 350 F. produced a small increase in the tensile strength. Precipitation heat treatment, however, produced marked property improvements, particularly in tensile strength, yield strength, and hardness in alloys containing higher percentages of silver. A solution heat treatment of 18 hours at 7'l0 F. iollovved by a precipitation heat treatment of 4.8 hours at 350 Bl, for example, in creased the Brinll hardness of the magnesium alloy containing 8 per cent of silver from 45.0 to 55.5 and the Brinell hardness value oi the magnesiuni alloy containing 12. per cent of silver from 51.0 to 65.5. Although beneficial property improvements are obtained in alloys containing approidmately 0.3 to l per cent of silver, I normolly, prefer to use from 0.5 to 8 per cent of silvenexcept in those cases where maximum properties in the heat treated condition are required, and then I prefer to use alloys containing approximately 4 per cent to 8 per cent of silver. Alloys with low percentages of silver are better adapted for plastic deformation operations, while alloys with higher percentages of silver are better suited for the production of castings.

Furthermore, l have discovered that the ad dition of silver to commercial magnesium is henc ilcial from the standpoint of corrosion resistance. This may beillustrated by alternate immersion corrosion tests conducted in a 3pc! cent salt solution. At'the end of 2% hours, pure magnesium had lost weight at the rate of 65.0 mg./cm. /day, while the magnesium alloys containing 2 per cent vof silver and d per cent of silver lost only 51.2

a 30 per cent decrease in the corrosion rate or metals aluminum, manganese, zinc is added to from 13,000 pounds per square inch to 18,000

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 025 per cent to 12 per cent, the percentage of zinc may from about 0.5 per cent to 8 per centfand the percentage of manganese may vary from about 0.1 per cent to 1 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 the percentages 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 percent 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, I normally 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 lfper cent.

The following examples serve 'to illustrate the beneficial eifect of silver in this class ofmagneslum alloys as expressed by improvements in physical-mechanical 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 percent 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 m esium alloy containing 0.2 per cent of manganese and 4,100 pounds per square inch for the zinary magnesium alloy containing 2 per cent of lver.

The addition of silver to magnesium-aluminum and to magnesium-aluminum-manganese alloys' has been found to be particularly beneficial when the alloys are 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 8 per cent of aluminum and 0.2'per cent of manganese from 34,000 pounds .per square inch to 36,000 pounds per square inch and 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, theaddition of 2 percent of silver to this same magnesium alloy containing 8 per cent of aluminum and 0.2 per cent of manganese increased the yield strength pounds per square inch and the Brinellhardnee-s from 58 to 84. V

The magnesium-silver-zinc and mlli esiume. silver manganese-zinc alloys are satisfactory for the production of wrought shapes. While both alloys can be extruded readily, the former issbetter for rolling and forging operations; since the an-- nealing temperature generally employed in such operations closely corresponds to the temperature at which precipitation of manganese occurs, and this precipitated manganese lowersthe ductility and workability of the alloy. Magnesium-silverzinc alloys, suitable for rolling, contain approximately 0.5 per cent to- 3 percent 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 inagnesium-silver-manganeseezinc alloyscontaining 0.5 per cent to 5 per cent of silver, 0.1 per centrto 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 this type of alloy to the extent of a few tenths of a per cent, and in such amounts has no appreciable efl'ect on physi-' cal property improvement, although it does im-' prove 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 of aluminum, 0.2 per cent of manganese, ands .per cent of zinc. This alloy, in the solution heat treated condition has atensile strength of 27,200 pounds per square inch, a yield strength of 13,000 pounds per square inch, 5 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 treated condition, this same alloy composition has the follewing.proDertie8,-tensile strength 31,000 pounds per square inch, yield strength 21,000 pounds per square inch, 0.5 per cent elongation, '12 Brinell hardness, and a single-blow impact value of 2.5 foot pounds.

I have likewise discovered that the corrosion 60 nig./cm.'/day to 1.7 mg./cm.=/day. In a sin'iilar fashion, the addition of 8 per cent of alurninum 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 mgJcmfl/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 oi? a 90-10 aluminum-manganese hardener.

This is a division of my co-pending application 20 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 in gredients and the steps herein disclosed, provided those stated by any of the following claims or- 7 their equivalent be employed.

I particularly point out and distinctly claim as my invention: I

1. A magnesium base alloy comprising from 0.3 to 12 per cent of silver, from 0.5 to 12 per cent of aluminum, from 0.1 to 1 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 6 per cent of silver, from 0.5 to 8 per cent of aluminum, from 0.1 to 0.8 per cent of manganese, and from 0.5 to 3 per cent of zinc, the balance being magnesium.

3. A magnesium base alloy comprising about 5 per cent of silver, about 5 per cent of aluminum, about 0.2 per cent of manganese, and about 3 per cent of zinc, the balance beingmagnesium.

v JOHN A. GANN.