US2087269A - Aluminum-calcium alloys - Google Patents

Description

Patented July 20, 1937 ALUMINUM-CALCIUM ALLOYS Philip '1.- Stroup, New Kensington, Pa; assignor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application April 29, 1936, Serial No. 77,020

4 Claims.

I This invention relates to aluminum base alloys containing calcium and it is more particularly concerned with a means of producing sound castings. I

Aluminum base alloys consisting of aluminum and 2 to 15 per cent calcium find commercial use both as material from which certain articles are made and as a source of calcium in the manufacture of other alloys. 4 I In making aluminum base alloys containing calcium it is preferable to add this element as a constituent in a rich alloy rather than in elemental form to avoid undue loss and excessive oxidation. Hence it is the customary practice to employ a calcium-bearing alloy of the kind mentioned above. 1

The manufacture of the aluminum-calcium alloys themselves involves some difficulty by reason of the readiness with'which they oxidize in the molten condition and their marked tendency to sorb gas from the atmosphere. The oxide particles formed on the surface of the metal appear to hold onto considerable gas when they become mingled with the molten metal and thus in eifect become a source of gas when conditions change and the particles are no longer able to retain their gas charges. This phenomenon of gas release is manifested during the solidification of the alloy. During this process the affinity between the metal, the oxide particles and the sorbed gas is greatly reduced and the gas forms bubbles in the liquid metal. If the metal is in a sufilciently fluid state the bubbles may escape, otherwise they are trapped and formspaces in the casting. Furthermore, in the case of the rich alloys, the void spaces contain gas which is released in the melt to which the alloys are i added. The deleterious effect of gas isthus transferred to other alloys.

o Aluminum-calcium alloys also exhibit another disadvantageous feature when solidifying, namely, the formation of excrescences on the head or upper surface of the castings which necessitates discarding this portion of the casting.

45 My invention is accordingly directed to a means of eliminating or greatly reducing the formation i of the void spaces in aluminum-calcium alloys,

65 spaces in the solidifying alloy and does away with the protuberances normally occurring on the top surface of the frozen alloy. '1 have found, for example, that the addition of 0.05 per cent sodium to an alloy composed of aluminum and 14 per cent calcium completely removes the objection- 5 able porosity ordinarily occurring in such an alloy. I have also found that such a sodium treated alloy does not introduce gas into other aluminum base alloys to which it may be added, thus carrying over the benefit of sodium into the 10 final product. t

In order to be effective the sodium should be added shortly'before the aluminum-calcium alloy is poured into the mold. In this manner the maximum amount of sodium is retained in the 1 alloy. This element must remain in the alloy, especially where the latter is to be added to another melt. I am aware that sodium has been heretofore employed in modifying the structure of aluminum alloys containing substantial 20 amounts of silicon, and in certain treatments when it iscompletely removed from the alloy after it has been added. My invention, however, is clearly distinguishable from such prior uses of sodium inthat I employ it to suppress the 25 'action of the calcium, and it is necessary to retain the sodium in the alloy to accomplish this purpose.

In referring to the proportions of sodium to be added to the molten alloy, allowance must be 30 made for the escape of a certain portion of the element because .of its volatility at the temperature of molten aluminum and its great tendency to burn. It is therefore usually necessary to add more sodium than is ultimately desired in the 5 alloy to compensateior any losses. In stipulating that 0.005 to 0.1 per cent sodium should be added to the herein described aluminum-calcium alloys, I mean that at least this amount of sodium should'remain in the final product. The 40 sodium is in fact a positive constituent of the alloy. If smaller amounts of this element than 0.005 per cent are employed, the benefit in respect to reducing porosity is negligible. On the" other hand, amounts larger than about 0.1 per cent do not show any commensurate effect upon the gas content of the alloy. For most purposes, however, I prefer to use no more than 0.05 per cent sodium because of the difliculty of adding I and retaining a larger amount of the element in the alloy. 7

The sodium should be added to the molten aluminum-calcium alloy in the elemental form. This is preferably done by wrapping pieces of the metal in aluminum foil, placing them in a persilicon, and the like.

suppress the action of calcium in promoting the formation of oxide particles and the sorption of gas. My invention is applicable to treating such alloys also since it pertains primarily to inhibiting the action of calcium. These alloys as well as the binary aluminum-calcium alloys are characterized by a relative freedom from gas, and the resultant porosity of the casting when 0.005 to 0.1 per cent sodium is present.

The term aluminum as herein employed refers to the metal containing the usual impurities of iron, silicon and the like. The calcium also may contain impurities usually associated with this metal.

I claim: 7

1. An aluminum base alloy containing. from 2 to 15 per cent calcium and 0.005 to 0.1 per cent sodium, said alloy being characterized by substantial freedom from porosity attributable to the presence of gas in the metal.

2. An aluminum base alloy composed of from 2 to 15 per cent calcium, 0.005 to 0.1 per cent sodium, and the balance aluminum.

3. An aluminum base alloy composed of from 2 to 15 per cent calcium, 0.005 to 0.05 per cent sodium, and the balance aluminum.

4. An aluminum base alloy composed of 14 per cent calcium, 0.05 per cent sodium, and the balance aluminum.

PHILIP T. STROUP.