US1932834A - Aluminum alloys - Google Patents

Description

Patented Oct. 31, 1933 ALUMINUM ALLOYS Robert T. Wood, Lakewood, Ohio, assignmto Aluminum Company of America, Pittsburgh, Pa., a corporation of'Pennsylvania No Drawing. Application February 25, 1932 Serial N0. 595,231

.2 Claims.

The invention relates to aluminum base alloys containing from about 2 per cent to about 9 per cent of magnesium. The invention has for its object the improvement of alloys of the abovementioned composition by the addition of from about 0.01 per cent to, 2.0 per cent of calcium. As one of its more specific objects the invention includes the provision of a desirable alloy of this class containing magnesium, manganese, and calm cium. Wherever in this specification and the appended claims the term aluminum occurs, it includes such impurities as ordinarily occur in aluminum. The term aluminum base alloys refers to alloys containing 80 per cent or more of aluminum.

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 chill-mold castings, although the nature of the difficulty differs somewhat in each case. In the case of sand castings, there occurs a reaction between the molten aluminum-magnesium alloy and the ordinary sand-mold material, or

vapors generated therefrom. There is also a reaction with the atmosphere. In addition, the aluminum-magnesium alloy does not flow freely through narrow sections at ordinary pouring temperatures, and if the pouring temperature be raised the solidified alloy. is unsound. If the aluminum-magnesium alloy be cast in a chillmbld the reaction effect is to some extent minimized but the troubles arising from cold-shuts and mis-runs are accentuated because of the more rapid chilling of the molten metal. These considerations apply with similar force to aluminum base alloys consisting of aluminum, magnesium, and manganese such as are disclosed and claimed herein. Aluminum base alloys containing magnesium in amounts between 2 per cent and 9 per cent exhibit marked tendencies to evolve gas during cooling from the molten to the solid state in a mold. This evolution of gas isharmful since a certain amount of 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 containing from about 2 per cent to about 9 per cent magnesium, the

difficulties described hereinabove are r to a considerable extent eliminated. The calcium should be present in amounts ranging from 0.01 per cent to 2.0 per cent subject to specific considerations as hereinafter disclosed.

In the melting of aluminum-magnesium alloys of the composition herein described, a viscous scum 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 resistanee 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 relatively small amountsof calcium, in preferred range between 0.01 per cent and 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 properties is immaterial. In amounts of more than 0.5 per cent,

the calcium has the advantages enumerated herein but has a tendency to lower some of the physical properties of the alloys. This effect on the physical properties is not harmful when the calcium is used in amounts less than 0.5 per cent, but when high'strength is not a desideratum the calcium may be used in amounts up to about 2 per cent. In intricate chill-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 0.01 per cent to 2.0 per cent of calcium is added to the alloys, the amount of gas evolved during solidification becomes less marked with increasing calcium content, and when, for instance, about 2 per cent of calcium is added to an aluminum base alloy containing about 9 per cent magnesium, the reduction of gas evolution is so marked that the molten metal cools to the solidification temperature with a smooth, mirrorlikesurface. Amounts as low as 0.01 per cent are found to be beneficial when added to aluminum base alloys containing from about 2 to 9 per cent of magnesium. I prefer to restrict the upper limit of the calcium to about 2 per cent since this is about the maximum amount which may be added without preventing the obtainment in the 119 alloys of the physical properties required for ordinary needs. If the best physical properties are desired, with an improved though not complete degree of gas prevention, I keep the calcium between 0.01 per cent and 0.5 per cent. 2

I have found that the addition of calcium in amount as disclosed hereinabove is also beneficial to alloys consisting of aluminum, magnesium, manganese, and calcium; which alloys are superi or in tensile strength, yield point, per cent elongation, and Brinell hardness to the alloy without manganese, and superior in casting properties and freedom from gas evolution to aluminum-magnesium-manganese alloys without the calcium. In the aluminum-magnesium-manganese-calcium alloy I produce an improvement over a range of from 0.1 per cent to 1.5 per cent manganese by the addition of from 0.01 per cent to 2.0 per cent calcium. As a preferred alloy I use an alloy consisting of about 4.0 per cent magnesium, about 0.5 per cent manganese, and about 0.2 per cent calcium in an aluminum base.

In compounding the aluminum-magnesiumcalcium alloy, I prefer to add the calcium to the molten aluminum by thrusting the calcium beneath the surface with a tongs or other suitable implement. After the calcium is alloyed, the magnesium can be added either in the form of commercially pure magnesium'or in the form of an aluminum-magnesium-rich alloy previously prepared. when an aluminum-magnesium-manganese-calcium alloy is to be prepared, it is preferably compounded by first adding to the molten aluminum the manganese, which is usually in the form of an aluminum-manganese-rich alloy. Since the melting point of an aluminum-manganese-rich alloy is higher than that of the other combinations involved, the best results are obtained when the melt is brought to a slightly higher temperature than for an alloy in which manganese is not used. The aluminum-manganese-rich alloy is then added and permitted to dissolve. As the melt cools the magnesium and calcium may be added in the manner described for the compounding of an aluminum-magnesium-calcium alloy.

Having thus described and explained my invention and the manner in which it may be practiced, I claim:

1. A metallic alloy consisting of about 2.0 per cent to 9.0 per cent of magnesium and about 0.01 per cent to 0.5 per cent of calcium, the balance being principally aluminum.

2. A metallic alloy consisting of about 2.0 per cent to 9.0 per cent of magnesium and about 0.01 per cent to 2.0 per cent of calcium, the balance being principally aluminum.

ROBERT T. WOOD.