US1570893A - Method of making aluminium-silicon-alloy castings - Google Patents

Description

1%.... Jan. 2a, 1926.

UNITED STATES PATENT ornca. A

.DOUGLAS 3. H0338, OI CLEVELAND, OHIO, ASSIGNOR 'IO ALUMINUM COMPANY OI AMERICA, A CORPORATION 01' PENNSYLVANIA.

. n'rnon or MAKING AnunInUu-smIcoN-Amoir cns'rmes.

Io Drawing.

Making Aluminum-Silicon-Alloy Castings,

of which the following is a specification.

This invention relates to aluminum allo s containing substantial amounts of silicon, and its object i to provide a simple method of making aluminum-silicon alloy castings.

with improved physical properties, such as tensile strength, yield point and hardness.

cry that the physical properties of cast alummum-silicon alloys, especially those which have been modified. by treatment with alkali metals or with alkali metal fluorides,

are greatly dependent upon the time which elapses between the' solidification of the castings in non-chilling molds and their attainment of room temperatures, or, more accurately, temperatures below about 250 C. 2 ;It is well known that sand cast aluminumsilicon alloys, containing siliconin amounts b from about 3 to 15 per cent do not ordinarily possess properties. much different from other sand cast aluminum" alloys, for example,

80 from an 8 per centcopper alloy. However, by a suitable procedure, commonly termed modifying, 1t is possible to greatly en hance their physical properties, so that such alloys at once become better adapted for 85 commercial use. The" modifying procedure may, for example, be that disclosed by A.- Pacz in U. S. atent No. 1,387,900 or that disclosed by J. D. Edwards, F. C. Frary and H. V. Churchill in U. 8. Patent No.

"40 1,410,461. Aluminum-silicon alloys untreated by any such method will hereinafter be. termed normal to distinguish them from the treated, or modifie alloys. As is already well known, such processes act to refine the grain of the alloy and to disperse highly the silicon particles.

. In carrying out my invention, I make'use of an alloy of aluminum containing fromv about 3 to 15'per cent silicon,- which may be made by stirring silicon into molten alu-- minum at 750 to 850 C. until solution is complete. In making castings, the alloy is The invention is based upon my discov- Application filed April 29, 1925. Serial No. 28,809.

preferably modified by treating it while molten with a suitable refining agent, say 0.1 per cent by weight of metallic sodium at a temperature of about 800 0., or' 2 per cent of. sodium fluoride at a temperature of about 940 Q, and allowed to cool to a suitable pourlng temperature, whereupon it is cast into a non-chilling mold, by which is meant a mold whose walls do not rapidly chill the molten alloy.- A suitable pouring temperature for an aluminum-silicon alloy containing 12, er cent silicon is approximately 650 higher freezing points, somewhat higher pouring temperatures may be required. As soon as practicable after the mold is filled, the casting is removed and quenched in a suitable liquid, referably water, in order to cool it as quic ly as possible to room temperature or .to a tem eratu're' below about 250- C. The physical properties are greatly im roved by this treatment and are materia y better than those of like alloys similarly treated with an alkali metal or an alkali metal fluoride fiux, but which are cooled normally to room temperature in sand molds.

.,'although with alloys of As an example of the improvement efiected merely by the modifylng treatment, a normal alumi-numalloy containing approximately 13 per cent silicon and approximately 0.5 per cent iron, showed an average tensile strength for two bars of'19 ,530 pounds per square inch and anelongation of 3.5

"per cent in twoinche's, when castand permitted to cool in sand in the form of a test bar 0.5 inch in diameter, the alloy being poured at 650 C. The same alloy, after being treated at 940 0., with 2 per cent of a refining flux (sodium fluoride) and cast similarly at 650 Q, had an average tenslle strength fortwo bars of 28,100 pounds per square inch and an elongation of 'Z .5 per cent in two inches. 2

The physical properties of such a modified alloy are further substantially improved if the casting is promptly removed from a nonchilling mold and suitably chilled. For example, by removing the bars from the molds shortly after pouring, i. e., while they are still relativel hot, and'quenching them in cold water, 1: e tensile strength and hard ness may be substantially increased. Thus .vlate variations in casting conditions, from the same 20-pound melt of modified aluminum-silicon alloy cited above, and quench ing bars at various times, I" found the prop erties to vary as follows Time before quenching Yield Tensile Elonga- Hardness of casting a point strength tlon Bnnell "in lag in Lbs IR/I in 74 seconds 18, 138 36, (75 6. 6 72 120 seconds 16, 138 33, 450 5. 5 66 163 seconds 16, 125 31, 915 1 5. 0 62 Cooled in mold to'room 1 temperature 13, 150 28, 100 7. 5 54 Thus it is seen that the tensile strength and hardness have been greatly improved as the result of the rapid cooling of the casting. Temperature measurements made by inserting an 18. gauge chromel-alumel thermocouple in the mold before pouring showed .that the temperature varied as follows, the

metal being at-650 C. when poured:

Time after Temperapouring U18 Minutes 0. 1 565 2 535 a. t 510 .4 485 5 470 10 350 I' have found further that if the iron content of these alloysis reduced, the physical properties are still further improved by my process. For example, a 20-pound melt of aluminum alloy containing approximately 13 per cent silicon and approximately 0.11

per cent iron, was treated with 2 per cent of the sodium fluoridemodifying flux at 930 C. and allowed to cool to 650 (1., whereupon it was poured into sand'm'olds, as before. Bars cooled to room temperature in the molds showed an average tensile strength for two bars of 24,890 pounds per square inch, a yield point of 11,830 pounds per square inch and 18.3 percent elon ation in two inches. Bars removed from t e molds and quenched in cold water within 90' seconds after pouring showed for two bars an average tensile strength of 34,150 pounds per-square inch, yield point 15,090 pounds per square inch, and 8.3 per cent elongation. Bars quenched at intermediate periods showed properties varying between these.

The castlng temperature and time elapsing before quenching ,will' naturally vary somewhat with the nature and. size of the casting, but I have found that in order to obtain improvement in propertiespf the test bars referred to above the bars should generally be quenched in less than five 'tical. The approximate temperatures of the bars, corresponding to these limits of time, were 470 and 510 C., respectively.

Quenching ten minutes after pouring castings of the size of test .bars does not alter appreciably: the properties obtained by slow cooling to room temperature,but it will be understood that in the case of large castings greater periods of time must elapse between castin and removal from molds than in the case 0 small castings.

' -I have also found that'by' applying this quenching process to normal, or unmodified, aluminum-silicon alloys, an improvement is effected, but it is not so, large as that obtained by applying it to the modified alloys.

As stated above, the" silicon content of the alloy is preferably from about 3 to 15 per cent. In the case of normal alloys the silicon content is ordinarily not greater than 5 to 10 per cent, while in the case of modilied alloys it is preferably from about 8 to 13 per cent. The invention is not limited to alloys containing only aluminum and silicon, but is applicable to aluminumsilicon alloys containing other elements,

such as copper, zinc and nickel.

In a copending application of R. S.

Archer and J. D. Edwards, Serial No.-

426,839, thereiis described the production of aluminum-silicon alloys of similar oomposition with improved physical properties, which comprises causing the alloy to solidify ra idly, as forwaxample, by casting in a 0 ill mold. As a result of this rapid solidification of the molten alloy, a very high dis ersion of the silicon particles is secured. y process is not concerned, however, with the rapid solidification of the molten metal, but with an improvement in the properties of the casting which can be effected by a rapid cooling of the czsting immediately after it' has solidified 1 a non-chilling mold, and is largely predicated on my discovery that the physicalproperties of the casting may be improved by rapid cooling after the casting has solidi fied sufficiently to remove itfror'n a mold.

My invention is particularl applicable. to

castings made in sand mo ds which normally permit a relativel slow rate of cooling of the casting as long as it stays in the mold. It may also be applied effectively in the case of castings made in metal molds as described in the above-mentioned application, but wliere the mold temperature was maintained too high to permit the obtainingof the improved physical properties resulting from chillihg of the casting. Such a heated metal mold is a non-chilling mold in the sense in which the term is herein used. In some cases a casting may be removed from a mold and uenched before it has completely solidifie internally, and in these cases an additional improvement may be secured by the rapid solidification of the interior sections oi produced by uenching.

The modification treatments used to improve the properties of aluminum-silicon alloys have for their ultimate eflect the high dispersion of the silicon particles, the normally relatively large plates and needles of silicon being thereby dispersed'as fine particles, even appearing globular in character. It is the maintaining of this high dispersion of the silicon particles which symbolizes my process in its preferred form. By removing the castin s from the mold as soon as they are rigi ,enough to handle, and then quenching in a sultable fluid, such as water, it appears that the silicon particles are cooled rapidly through a temperature range in which they. nor-- mally grow to some extent, and this growthi which lowers the hardness, yield polnt strength, is thereby inhibited. It is also probable that my process retains in solid solution a greater proportion of silicon than normally obtains on slowcooling of a casting of similar composition and the strength of the casting is thereby improved.

According to the provisions of the patent statutes, I have explained the principle and mode of o eration of my invention, and have specifica y described the preferred manner of practicing it as to temperature, compositions and cooling periods. However, I desire to have it understood that,

within the scope of the appended claims,

the invention may be practiced otherwise than as explained in the specific examplps given.

I claim:

1. The method of making aluminum-silicon alloy castings, comprising filling a nonchilling mold w1th molten aluminum-silicon alloy, promptly removing the casting from the casting.

the mold after initial solidification, and

chilling the casting.

rapid il y 2 he method of making aluminum-Sill con 'alloy castings, comprising filling a sand moldxwith molten aluminum-silicon alloy,-

4. The method of making castings of aluminum-silicon alloy, comprising filling a sand mold with molten aluminum-silicon alloy which has been treated with a reagent capable ofrefining the grain and dispersing the SlllCOIl partlcles, removing the cast-- ing from the'mold after initial solidification, and rapidly chilling the casting.

5. The method of mak ng castings from an aluminum-silicon alloy containing from about 3 to 15 per cent silicon, com rising filling a nonchilling mold with sai, alloy in a molten condition, promptly removing the casting from the mold after initial solidification, and rapidly chilling the cast ing by quenching it in a quenching 1i uid.

6. The method of making castings .rom an aluminum-silicon alloy containing from about 8 to 13 per cent silicon, comprising filling a non-chilling mold with said alloy in a molten condition and after being treated with a reagent capable of refining the,

' grain and dispersing the-silicon particles,

removing the casting the casting by quenching it in a quenching liquid. 7

In testimony whereof I sign name.

m noucnas- B. fionns;

from the mold after initial solidification, and rapidly chilling