US1934281A - Aluminum-silicon alloy - Google Patents

Description

Patented Nov. 7, 1933 UNITED STATES PATENT OFFICE ALUIHINUM- SILICON ALLOY No Drawing. Application January 30, 1936 Serial No. 424,726,

4 Claims.

The invention relates to aluminum-silicon casting alloys and it is particularly concerned with new alloy compositions having improved casting properties.

5 The use of aluminum alloys in cast articles has received considerable impetus in recent years because of the adaptability of these alloys to various conditions of casting practice and their desirable combination of strength, lightness and excellent appearance in the cast condition. Among those aluminum alloys which have obtained wide-spread application in the casting art the aluminum-silicon alloys containing substantial amounts of silicon are, in importance and extensive use, second only to aluminum base alloys containing copper.

The physical properties of aluminum-silicon alloys, including their resistance to the corrosive agencies commonly encountered, are especially advantageous for small and intricate castings such as motor parts and miscellaneous fittings, and for east articles such as cooking utensils, as well as comparatively large structural shapes of various design. The aluminum silicon alloys generally used for these purposes contain between about 3 to 15 per cent of silicon together with a small amount of iron as impurity, and sometimes copper, nickel, zinc, magnesium or similar alloying elements added in varying amounts to impart certain particular and beneficial properties. Among alloys of this type the aluminum-silicon-copper alloys are, for example, well known. Alloys containing somewhat smaller amounts than 3 per cent of silicon together with copper, nickel, etc., are used to some extent for casting purposes.

When, however, aluminum-silicon alloys are cast there are often formed small depressions or holes on the surface of the casting which are usually known as shrinks or draws. These are apparently due to shrinkage at the boundaries of the grains within the metal. In any casting these shrinks are undesirable, and in many cases they are so numerous and their effect on the strength, appearance and other properties of the casting is so objectionable as to preclude the use of the casting for its intended purpose, thus necessitating numerous rejections of castings which otherwise are perfectly good.

The present invention is predicated upon my discovery that this serious tendency of aluminumsilicon alloy to form shrinks or draws on solidification may be inhibited, in some cases completely, by the presence of a small amount of titanium in the alloy, and I have found that the addition will allow the use of aluminumsilicon alloys for castings which had not heretofore been considered possible with these alloys. Furthermore, the addition of the titanium to these alloys does not appear to decrease their natural strength.

One of the desirable features of my invention is the small amount of titanium required to eliminate these shrinks or draws. I have determined that the amount of alloyed titanium which will produce the most beneficial results may vary slightly according to the particular aluminum-silicon alloys with which it is used but will usually fall within the range of 0.1 to 0.5 per cent. Ordinarily it is not necessary to have present in the alloy more than about 0.1 to 0.2 per cent of titanium. In some cases the titanium content may be even less. Greater amounts ithan 0.5 per cent may be added but the segregation caused by the high melting titanium constituent which is formed when titanium is added to aluminum makes it inadvisable to exceed this concentration.

In any casting operation there are, as is well known, a number of variables, many of them 8 elusive and diflicult to control, which must be favorably adjusted before good castings can be obtained, but even the most careful observance of these well known conditions is insufficient, in the case of aluminum-silicon alloys, to secure uniformly good castings in respect to freedom from shrinks and'- draws, whereas with my aluminum-silicon-titanium alloy this important uni" formity of results is readily obtainable when conditions which are known to give poor results are avoided.

In casting the alloy the best results will be obtained if the temperature of. the molten metal be kept as low as possible consistent with proper pouring and the time of holding the metal molten before pouring the casting be not too long. However, in the usual foundry practice it is at times necessary to pour at a higher temperature because of the casting design and section thickness or to hold the metal molten for a considerable time before pouring. This latter practice will have an injurious tendency which I have found to be offset by the use of titanium as described in this specification.

The manner in which titanium is added to the alloy is not important and in so far as the final result is concerned, any of the well known methods of addition may be used. However, the usual precautionsemployedwith good melting and casting practice should be observed. It has been found advantageous to add the titanium in the course of. the electrolytic production of the aluminum rather than to add it to the final aluminum-silicon alloy. A titanium-bearing ore, for example titanium oxide, or alumina containing titanium oxide, may be added to the fluoride bath in the electrolytic pot, so that the titanium compound will, during the reduction process, be reduced to metallic titanium which will alloy with the aluminum. Silicon may then be added to this titanium-bearing aluminum in any convenient form, such as a silicon-rich aluminumsilicon alloy, or as metallic silicon. The aluminum which is used in making these alloys may be of any commercial grade or may be aluminum of the highest purity. Usually, however, it is ad vantageous for economic reasons to use aluminum of commercial grade, though containing small amounts of iron and other impurities.

Castings of the aluminum-silicon-titanium a1- loy may be made from the untreated molten alloy and also from the alloy which has, before casting, been treated to modify or improve its internal structure. Treatments for such purposes are well known and may consist, for example, in the addition of metallic sodium or potassium or a compound or compounds thereof to the molten alloy directly before casting. The ultimate eifect of this treatment is to produce a casting having substantially higher strength and ductility than is found in the so-called unmodified alloy.

The importance of the elimination of the shrinkage defect in aluminum-silicon alloy may be illustrated by the case of a large foundry which makes a variety of cast aluminum cooking utensils of more or less intricate design. This foundry had encountered the usual difficulty in obtaining good castings of aluminum-silicon alloys containing 5 per cent of silicon, particularly in some of the more intricate castings, these latter always showing so large a number of shrinks or draws on their surface as to be unsuitablefor use. Because of this it was found necessary to substitute for the aluminum-silicon alloy an aluminum-copper alloy containing 5 per cent of copper which, although not entirely overcoming the difficulty, made posisble the production ofa better casting. This substitution, however, was objectionable because of the inferior corrosionresisting properties of the aluminum-copper alloy. But with aluminum-silicon alloy containing 5 per cent of silicon to which there had been added, in accordance with my discovery, 0.1 per cent of titanium, the trouble was obviated and castings were regularly produced of a quality which had theretofore been considered impossible. This specific instance is given only by way of illustration.

The term aluminum-silicon-titanium alloy is used in the appended claims as a generic expression to include the following alloys and none other: (a) Alloys consisting entirely of aluminum, silicon, and titanium; and (b) alloys consisting of aluminum, silicon, titanium, and one or more metals of the class composed of copper, nickel, zinc, magnesium and the like; the titanium in each case serving to substantially inhibit the formation of surface shrinks or draws in casting the alloy.

It is to be understood that the invention is not limited to the specific details herein described but may be carried out in other ways without departure from its spirit.

I claim- 1. An aluminum-silicon-titanium casting alloy composed chiefly of aluminum, having about 3 to 15 per cent silicon and about 0.1 to 0.5 per cent titanium, the latter element serving to substantially inhibit the formation of surface shrinks or draws when the alloy is cast.

2. An aluminum-silicon-titanium casting alloy composed chiefly of aluminum, having about 3 to 15 per cent silicon and about 0.1 to 0.2 per cent titanium, the latter element serving to substantially inhibit the formation of surface shrinks or draws when the alloy is cast.

3. An aluminum base casting alloy consisting of silicon between about 3 and 15 per cent, titanium between about 0.1 and 0.5 per cent, and the balance aluminum, characterized, in the cast condition, by substantial freedom from surface shrinks or draws.

4. An aluminum base casting alloy consisting of silicon between about 3 and 15 per cent, titanium from about 0.1 to about 0.2 per cent, and the remainder aluminum, characterized, in the cast condition, by substantial freedom from surface shrinks and draws.

THERON D. STAY.