US2075517A - Aluminum alloy - Google Patents

Description

Patented Mar. 30, 1937 PATENT. OFF/ICE ALUMINUM ALLOY John G. G. Frost and Walter Bonsack, Cleveland,

Ohio, assignors to The National smelting Company, Cleveland, Ohio, a corporation of Ohio No Drawing.

Application October 4, 1935, Serial 8 Claims. (01. 15-147) This invention relates to alloys, and more particularly aluminum base alloys having a low thermal expansion and high thermal conductivity.

In the making of cast articles, such as pistons,

cylinder heads and similar articles utilized in internal combustion engines and motor constructions, it is desirable to make such articles from aluminum and alloys thereof because of their 10 low specific gravity.

While aluminum and aluminum alloys in general have a high thermal expansion, some aluminum alloys have been developed with a considerably lower thermal expansion, making them more desirable for use in the manufacture of castings for motor parts.

It has been found, however, that, in addition to having a low thermal expansion, aluminum alloys for use in making motor part castings should also have a high thermal conductivity, as well as good mechanical and physical properties, such as hardness, machinability and suitable strength at the elevated temperatures occurring in internal combustion engines.

It is, therefore, an object of this invention to provide a light weight aluminum base alloy having a comparatively low thermal expansion and a comparatively high thermal conductivity, and also having suitable mechanical and physical properties for the casting of motor parts and other similar articles requiring similar properties.

Another object of this invention is to provide such an aluminum base alloy which is readily machinable, which may be readily cast in the 5 usual type of molds, and which has a fine, ho-

mogeneous grain structure, and which may be subjected to elevated temperatures without causing grain growth or loss of strength.

While certain aluminum-silicon alloys are known to have a relatively low thermal expansion and relatively high thermal conductivity as compared to other aluminum alloys, it is necessary with these aluminum-silicon alloys to have the other desirable properties of hardness, machinability and good bearing qualities to make them more suitable for the production of pistons and other motor parts, and it is an object of this invention to provide such an aluminum-silicon alloy with such' desirable mechanical properties and still maintain the relatively low thermal expansion and relatively high thermal conductivity of these alloys.

The addition of magnesium to aluminum-silicon alloys increases their hardness and tensile 55 strength, and increases their elastic properties,

and, in the amount desirable to give these properties, has little or no effect on the low thermal expansion and high thermal conductivity.

It has been discovered that if tin is added in proper proportions to aluminum base alloys containing silicon it will increase the thermal conductivity without materially affecting the thermal expansion of the alloy. Tin also improves the machinability of the alloy, and provides better bearing qualities in castings made therefrom. 10

excellent properties for the manufacture of ar- 15' ticles of this nature.

In preparing our improved aluminum base alloy, silicon is used as the predominating ingredient and may be present in amounts ranging from 7% to 20%. Proportions of silicon greater than 7% are more effective in reducing the thermal expansion of the alloy. It is desirable, however, to avoid the use of too large a proportion of silicon, since it has a tendency to segregate out in large crystals, unless the casting is chilled very rapidly. It is, therefore, preferable to use silicon in an amount from 11% to 15%.

Tim is an important addition to the aluminumsilicon alloy in order to provide better thermal conductivity and bearing qualities, as well as to improve its machinability. In order to obtain these properties, tin may be present in the amount of .3% to 3%, and preferably in an amount from .5% to 1.5% or 2%.

Many types of castings where rapid heat transfer is desired, such as for compressors, motor parts and other purposes where the castings are subjected to elevated temperatures, or even for refrigerator parts and other uses where the castings are used at low temperatures, can be advantageously made of an alloy of aluminum, silicon and tin, without magnesium.

In order to increase the hardness of the alloy when it is subjected to heat treatment, and to produce an alloy having desirable machinable qualities, it has been found that the addition of magnesium is advantageous. This may be in an amount from approximately .1% to 2%, and

preferably magnesium is utilized in an amount up to 1%, such as substantially .5% -to .9%, as as excess of magnesium has a tendency to render the alloy brittle, and a tendency to reduce the thermal conductivity of the alloy to too great a degree.

When present in small amounts up to apmal conductivi proximately 3%, zinc has the eflect of improving the mechanical properties such as increasing the tensile strength and hardness of the metal. When added in amounts such as 2% to 3% it tends to reduce the thermal conductivity of the alloy and to increase the thermal expansion. If relatively high thermal conductivity and relatively low thermal expansion are desired, it is preferable to have zinc present in amounts less than 2%, such as .5% to 1.5%, and when present in these amounts the thermal conductivity and thermal expansion of the alloy are not materially aflected.

Copper may be present in the alloy in small amounts, for in amounts such as .6% or less it does not seem to materially afiect the thermal expansion of the alloy, and it is, therefore, not

necessary, in making the alloy, to exclude base metals containing small amounts of copper. If copper is present in the alloy in the amount of approximately 1% or more, it has the effect of,

substantially reducing the thermal conductivity of the alloy.

If relatively high thermal conductivity of the alloy is desired, copper should not be present in an amount more than approximately 2%, but when such a high degree of thermal conductivity is not necessary, the copper may be present in amounts up to about .6% or more. I

Chromium, manganese, nickel, cobalt and titanium tend to reduce the thermal conductivity of aluminum-silicon alloys. These metals also have a tendency to form compounds with aluminum at a high melting point, and such compounds tend to segregate from the molten metal before solidification occurs. When a relatively high thermal conductivity of the alloy is desired, the above metals should not be present in an amount suflicient to materially reduce the thermal conductivity, and, if present at all, should only be present in such minimum amounts as are practicable in the commercial manufacture of the alloy, or as will not reduce the thermal conductivity beyond the limit desired for the alloy. Iron also has the tendency to reduce therbut iron, as is well known, is usually present an impurity in aluminum or aluminum alloys. However, it should not be present in an excessive amount, such as 1% or more.

As illustrations of our improved alloys the following specific examples are given:

An alloy containing 13% silicon, 1% tin, .5% magnesium and approximately .1% copper, and the balance aluminum and inner impin'ities, was chill cast and aged for 15 hours at 200 C. Upon being tested it was found to have a thermal expansion of 19.9 10 per degree centigrade between a temperature range of 20 and C. It also had a thermal conductivity of .38 calories per square centimeter per second at 30 C.

In an alloy having the same composition as above, except that 1%'copper was included instead of approximately .1% copper, the coeflicient of thermal expansion was substantially the same, while the thermal conductivity was approximately .36 calories per square centimeter per second at 30 C. after being aged at 20050.

For some purposes, where a high degree of' machinability is not so essential, the quantity of magnesium in the alloy may be substantially reduced or practically eliminated, and the alloy has a low coefficient of thermal expansion and high thermal conductivity. An example of such an alloy is an alloy containing 13% silicon, 1%

tin and the balance aluminum and nnnor impurities, which was chill cast and aged for 15 hours at 200 C. Upon being tested it was found to have a thermal expansion of approximately 20 10- per degree centigrade between a temperature range of 20 and 100 C., and it also had thermal conductivity of .37 calories per square centimeter per second at 30 C. With the same alloy, with the exception that the amount of tin was 2%, instead of 1%, the thermal conductivity was approximately .38 calories per square centimeter per second at 30 C., and the thermal expansion was the same.

In an alloy containing 13% silicon, 1% tin and .5% magnesium the coejicient of thermal expansion was substantially the same as that of the alloys given above, and the thermal conductivity was approximately .37 calories per square centimeter per second at 30 C., whereas when the amount of magnesium was increased to 1% in this alloy, the silicon and tin content being the same, the thermal conductivity was approximately .33 calories per square centimeter per second at 30 C.

As previously stated our invention contemplates that copper may be present in small amounts in the alloy and it is also to be understood that minor impurities may be present without departing from the scope of the invention set forth in the claims.

Low thermal expansion and high thermal conductivity alloys containing aluminum, silicon and tin are described and claimed in our copending application, Serial No. 96,517, filed August 17, 1936; aluminum base alloys having similar characteristics and containing aluminum, silicon, tin and zinc are described and claimed in our copend ing application, Serial No. 96,519, filed August 17, 1936; and aluminum base alloys of a similar character, containing aluminum, silicon, tin, magnesium and 'zinc, are described and claimed in our copending application, Serial No. 96,518, filed August 17, 1936.

Furthermore, it will be understood that the present invention is not limited to the specific details set forth in the foregoing examples, which should be construed as illustrative, and not by way of limitation, and in view of the numerous modifications which may be effected therein with out departing from the spirit and scope of this invention, it is desired that only such limitations be imposed as are indicated in the appended claims.

What we claim is:

1. A machinable aluminum base alloy having a low coeflicient of thermal expansion and high thermal conductivity, comprising about 11 to 15% silicon, about .5 to 2% tin, about .5 to .9% magnesium, with the balance substantially all aluminum.

2. A machinable aluminum base alloy having a low coefiicient of thermal expansion and high thermal conductivity comprising 7 to 20% silicon, .3 to 3% tin and .1 to 2% magnesium with the balance substantially all aluminum.

3. An aluminum base alloy having a low coemcient of thermal expansion and high thermal conductivity comprising about 11 to 15% silicon. .3 to 3% tin and .1 to 2% magnesium with the balance substantially all aluminum.

4. An aluminum base alloy having a low coefllcient of thermal expansion and high thermal conductivity, comprising about 11 to 15% silicon, about .5 to 2% tin, .1 to 2% magnesium, with the balance substantially all aluminum.

5. An aluminum base alloy having a low coefllcient of thermal expansion and high thermal conductivity, comprising about 11 to 15% silicon, about .5 to 1.5% tin, .1 to 1% magnesium with the balance substantially all aluminum.

6. An aluminum base alloy having a low coemcient of thermal expansion and high thermal conductivity, comprising about 11 to 15% silicon, about .5 to 2% tin, about .5 to 1% magnesium,

with the balance substantially all aluminum, said alloy having a coemcient of thermal expansion as cast of approximately 20x 10-, or less, per degree centigrade between a temperature range of 20 and 100 C. and having a thermal conductivity oi approximately .33 calories or more per square centimeter per second at 30 C.

"l. A piston formed from an aluminum base al- 10y having a low coeflicient of thermal expansion and high thermal conductivity comprising about 11 to 15% silicon, .1 to 1% magnesium, about .5 to 1.5% tin with the balance substantially all aluminum.

8. A chill casting formed from an aluminum base alloy having a low coemcient or thermal expansion and high thermal conductivity, comprising about. 11 to 15% silicon, .5 to 3% tin and .5 to 1% magnesium, with the balance substantially all aluminum.

JOHN G. a. mom. WALTER aonsacx CERTIFICATE OF CORRECTION.

Patent No. 2,075,517. March 30, 1937.

JOHN G. G. FROST, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 55, for the word "inner" read minor; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 1st day of June, A. D. 1957.

Henry Van Arsdale (Seal) Acting Commissioner of Patents.