US1932872A - Aluminum alloys - Google Patents

Description

Patented Oct. 31, 1933 ITE STATES PATENT OFFICE ALUll/IINUM ALLOYS Robert '1. Wood, Cleveland, Ohio, assignor m Aluminum Company of America, Pittsburgh, Pa, a corporation of Pennsylvania 2 Claims.

The invention relates to aluminum base alloys containing from about 2.0 to 9.0 per cent by weight of magnesium, from about 0.1 to 4.0 per cent by weight of manganese, and about 0.05 to 0.4 per cent by weight of at least one of that class of elements herein defined to be antimony and bismuth. The invention has for its object the improvement of alloys of the above-mentioned composition by the addition of from about 0.05 to 2.0 per cent by weight of calcium. This application is a continuation of my copending application Serial No. 634,154 which is a continuation in part of my copending application Serial No. 595,231.

Considerable difiiculty has heretofore been encountered in attempts to commercially produce.

castings of aluminum base alloys containing substantial amounts of magnesium. This difficulty is encountered both in the making of sand castings and permanent mold or chill-mold castings, although the nature of the difiiculty differs somewhat in each case. In the case of sand castings there occurs a reaction between the molten aluminum alloy containing magnesium and the ordinary sand-mold material, or vapors generated therefrom. In addition, the aluminummagnesium alloy does not flow freely through narrow sections at ordinary pouring temperatures, and if the pouring temperature be raised the resulting casting is unsound. If the magnesum-containing aluminum alloy be cast in a chill-mold the reaction effect is minimized to some extent but troubles arising from coldshuts and miss-runs are accentuated because of the more rapid chilling of the molten metal. These considerations apply with similar force to aluminum base alloys containing magnesium and manganese with or without antimony and/or bismuth such as are disclosed herein. Aluminum base alloys containing magnesium exhibit marked tendencies to evolve gas during cooling from the molten to the solid state in a mold. This evolution of gas is harmful since a certain amount 01' it is entrapped by the solidifying metal and tends to cause porosity and, therefore, unsound castings.

I have discovered that when calcium is added to aluminum base alloys of the type described herein, the difiiculties above described are, to a considerable extent, eliminated. The calcium should be present in amounts ranging from 0.05 per cent to 2.0 per cent by weight subject to specific considerations as hereinafter disclosed' In the melting of aluminum alloys of the composition herein described, a viscous scum often forms at the surface of the molten metal. Failure of the molten metal to run properly through narrow mold apertures is caused, in part, by shreds or particles of this scum being suspended in the molten metal and offering a resistance to the free passage of the metal through the apertures. Regardless of the cause of this low fluidity, I have discovered that the addition to the alloy of relative small amounts of calcium, in preferred range between 0.05 to 0.5 per cent, improves the casting characteristics to a very considerable extent and simultaneously effects a reduction of the scum or dross collecting at or near the surface. In the casting of articles in sand molds, I prefer to add calcium in amounts less than about 0.5 per cent except in instances where some reduction of tensile strength or other mechanical property is immaterial. In amounts of more than 0.5 per cent the calcium addition produces the advantages enu- -merated herein but has a tendency to lower some of the physical properties of the alloys. This effect is not harmful when calcium is added in amounts less than about 0.5 per cent, but when high strength is not a desideratum, the calcium may be used in amounts up to about 2.0 per cent. In intricate permanent mold castings where casting troubles are very serious if no calcium be added, the improved physical properties obtained coincident with the production of good castings more than offset the diminution in properties which might otherwise result from the use of the calcium.

I have discovered that when calcium is added to aluminum base alloys containing magnesium, the amount of gas evolved during solidification of the alloys is considerably reduced. When from about 0.05 per cent to 2.0 per cent by weight of calcium is added to the alloys, the amount of gas evolved becomes less marked with increasing calcium content, and the reduction of gas evolution may be so marked that the molten metal cools to the solidification temperature with a smooth mirror-like surface. I prefer to restrict the' amount of calciumzadded to 2.0 per cent or less since above this amount the physical properties of the alloys may be too seriously affected. If the best physical properties are desired, with an improved, although .not complete, degree of gas prevention, I keep the calcium content between 0.05 per cent and 0.5 per cent.

When calcium is added in the amounts above described to aluminum base alloys containing 2.0 to 9.0 per cent of magnesium and 0.1 to 4.0

per cent of manganese, the casting properties of the alloy are much-improved and the resulting castings are sound because of the elimination of much or all of gas evolution in the molten alloy before and during casting. Of such alloys consisting of aluminum, magnesium,

1 manganese, and calcium, the preferred alloys are those containing 2.0 to 9.0 per cent of magnesium, 0.1 to 1.5 per cent of manganese, and 0.05 to 2.0 per cent of calcium, the balance being principally aluminum. An excellent alloy for general foundry purposes is one containing about 4.0 per cent magnesium, about 0.5 per cent manganese, and about 0.2 per cent calcium, the balance being principally aluminum.

The aluminum alloys containing magnesium, manganese, and calcium are further improved, particularly as regards their strength and elongation at high temperatures, by the addition of about 0.05 to 0.4 per cent of at least one of that class of elements herein defined to be antimony and bismuth. Alloys of the above-mentioned compositions including antimony and/or bismuth in total amount not exceeding 0.05 to 0.4 per cent are extremely useful.

The alloys herein described may be produced by the usual methods of alloying metals. The calcium is preferably added to the molten alloy by thrusting the calcium beneath the surface with tongs or other suitable instrument.

The aluminum used in preparing the alloys may be pure or it may contain the impurities found in commercial grades of this metal. Ordinarily a good commercial grade of virgin aluminum will give excellent results and is preferable.

I claim:

1. A metallic alloy consisting of about 2.0 to 9.0 per cent by weight of magnesium, about 0.05 to 2.0 per cent by weight of calcium, about 0.1 to 4.0 per cent by weight of manganese, and about 0.05 to 0.4 per cent by weight of at least one of the class of metals composed of antimony and bismuth, the balance being aluminum.

2. A metallic alloy consisting of about 2.0 to 9.0 per cent by weight of magnesium, about 0.05 to 2.0 per cent by weight of calcium, about 0.1 to 1.5 per cent by weight of manganese, and about 0.05 to 0.4 per cent by weight of at least one of the class of metals composed of antimony and bismuth, the balance being aluminum.

ROBERT T. WOOD.