US2807540A - Aluminum base bearing - Google Patents

Description

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7 2,807,540 I ALUMINUM BASE BEARING Alfred W. Schluchter, Dearborn, Mic 11., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware 7 4 Claims. (Cl. 75-142) This'invention relates to an aluminum base alloy and particularly 'to an improved alloy of this type having properties rendering it especially suitable for use as a bearing material.

Many aluminum base bearing alloys, such as the type disclosed in Patent No. 2,238,399, which issued April 15, 1941, in the name of Alfred W. Schluchter, are satisfactory bearing materials in most respects. However, such alloys cannot be satisfactorily heat treated so as to provide sufficient hardness for many purposes. Ac cordingly, a principal object of my invention is to provide an aluminum base bearing alloy which can be heat treated so that it possesses a hardness comparable to that of any conventional hardenable aluminum alloy and which, at the same time, can be rolled into strip form by conventional commercial methods.

- A further object of this invention is to provide such a heat treatable aluminum alloy which has good score resistance when used as a bearing. Aluminum and most of its alloys are generally quite unsuitable for use in bearings for machine parts of iron for the additional reason that aluminum tends to adhere to, or combine with, the ferrous metal, thereby causing scoring or seizing. I have found, however, that by a suitable combination of alloying constituents this difficulty can be overcome and an alloy produced having not only excellent anti-friction properties but other characteristics especially desirable in a bearing material.

In accordance with my invention, therefore, the foregoing and other objects and advantages are attained to a particularly high degree in an aluminum base alloy con- 2,807,540 Patented Sept. 24, 1957 'ice having a correspondingly longer fatigue'life. As a result of this hardness, solid bearings made from this alloy also retain their original shapes much better than many of the bearings which heretofore have been made of softer alloys. The former do not take a set at temperatures to which they are normally subjected, and they undergo a negligible amount of shrinkage when removed fromen raining copper, magnesium, cadmium and silicon. Inasmuch as the alloy thus produced is a much stronger metal than the aluminum alloys generally heretofore used for bearing purposes, solid bearings may be made from it, no backing of steel or similar metals being necessary for many applications. Of course, this alloy can also be readily bonded to steel and many other metals and can be used on a backing of such metals. Moreover, if desired, a bearing formed from my alloy may be advantageously provided with a thin'overlay of lead or a lead base alloy. Examples of these overlays include the lead-tin and lead-indium alloys which are used for this purpose and in which the lead is the major C011, stituent. Hence it is obvious that, as well recognized by the trade, the term bearing is used herein as meaning an element which performs a bearing function regardless of the presence or absence of such an overlay.

gin'es after extensive use. Despite these aforementioned properties, the alloy can be easily rolled down by conventional methods.

In accordance with my invention, highly satisfactory bearing properties are obtained with an alloy having the following composition by weight: 0.05% to 3.0% magnesium, 0.05% to 5.0% cadmium, 0.3% to 11.0% silicon, 0.1% to 3.0% copper and the balance substantially all aluminum. Various incidental impurities may be in cluded in this alloy in the usual small amounts without any substantial detrimental effects. For example, iron, which together with silicon is present in commercial aluminum, may be present in amounts up to 0.5% without causing any harmful results. Under severe test conditions, alloys having the above composition show excellent anti-friction properties so that bearings formed of this alloy not only do not score or gall when in contact with a rotating steel shaft, but neither the shaft nor the bearings show an appreciable amount of Wear after long and severe use. I have also found that the resistance of this alloy to cracking or crumbling is extraordinarily high.

The magnesium is added to increase the hardness of the bearing alloy, a magnesium content of only 0.05% being sufficient to provide a sufficient degree of hardness for many applications. Inasmuch as the molten magnesium tends to oxidize during the alloying procedure, however, for best results it is preferable that the magnesium be added in amounts equal to at least 0.2% of the weight of the alloy. 'Magnesium has anadverse effect on score resistance and friction properties, however, and as a result the magnesium content should not be higher than approximately 3.0%.

With additions of magnesium in amounts greater than approximately 0.5%, the increase in hardness is relatively slight. Moreover, if the magnesium content is not higher than this amount, theaddition of copper tends to offset the adverse effect of magnesium on the score properties of the alloy. Accordingly, a magnesium content ranging from 0.2% to 0.5 is preferred, approximately 0.5% magnesium generally being the optimum amount to be added. V

The addition'of cadmium greatly improves the score resistance of the alloy. Despite the fact that it has been generally recognized that the addition of cadmium to aluminum causes slight loss of strength, I have found that cadmium, in the presence of silicon, may be beneficially introduced in amounts as large as 5.0% without causing a measurable loss of strength. 7 In fact, the resultant alloy is remarkably resistant to disintegration under impact or pounding such as occurs in severe bear-t ing service. Moreover, thepresence. of cadmiurndocs not affect the hardness if the alloy issubsequently hmt treated. Although the effect of cadmium on both strength and hardness is negligible in anyoevent if added in quantities no greater than 5.0%, cadmium is a relatively soft metal and hence the cadmium content should not be higher than this amount. v

I have also found that a cadmium content greater than 5.0% tends to cause this element to segregate out and settle to the bottom of the casting during the solidification thereof in the form of the apparently nearly pure, metal. Thus, too high a cadmium content raises the cost of the alloy by increasing personnel expenses because of increased handling costs and the necessity, ofmore detailed andcareful' supervision. Moreover, inasmuch as cadmium is also a relatively expensive and somewhat rare metal, it is desirable to add only as much of this metal as is necessary to produce the desired results.

There is a marked improvement 1 in score properties it cadmiumis added in quantities up to 2.5%, but increasing the cadmium content beyond this amount does. not an preciably increase the. score ,resistance of the alloy. Hence, cadmium preferably should be present in an amount ranging from approximately 0.2% to 2.5% in order to provide the most desirable anti-friction proper= ties. Inasmuch as cadmium also tends to volatilize at the temperature of molten aluminum, however, it often may be desirable to add slightly greater amounts of cadmium to oflsetlanylosses. due tothis tendency for volatilization. Arcadmium contentof at least 0.5% is necessary in all instancesto, provide adequate score resistance.

Theinclusion of silicon in my aluminum base bearing alloy alsoenhances itsscore resistance. This property of silicon, plus the manner in which it influences the effects of the cadmium present in the alloy and the fact that solidification shrinkage is lower as the silicon content is. raised, dictates that the alloy contain at least 0.3% silicon. Inasmuch as a high silicon content interferes with rolling processes,.however, the maximum amount of silicon. to be added necessarily is governed by the method in which the article, such as a bearing, is formed. Accordingly, silicon. should not be present in amounts greater than 5.0% in the wrought alloy because such an alloy needs to be rolled, while it may be added in amounts as high as 11.0% in the cast alloy. While an increased I silicon content improves score resistance, the addition of silicon in amounts greater than 5.0% provides only slight additionalbeneficial properties in this respect. Accordingly, .best results are obtained for most purposes when the siliconcontent is kept within a preferred range of 2.0% to 5.0%.

Theaddition of copper, in conjunction with the mag nesium present in the aluminum base alloy, contributes to the hardenability of the resultant alloy. The hardness of the alloy will be reduced to too great an extent if the copper content is below 0.1%, and the addition of at least 0.3 copper is preferable in order to obtain a satisfactory degree of hardness in those applications where this property is ofprime importance. Where even greater hardnesswis desired, amounts of copper as high as 3% may be added and, in the case of the cast alloy, the copper content may be as high as 5% in some instances. Copper should notbe present in amounts greater than about 3% in the wrought alloy, however, because of the difficulties which would otherwise be encountered in rolling operations due to the reduction in .ductility of this alloy. In general, theincrease in the hardness of the alloy resulting from the addition of copper in quantities above approximately1% is not substantial if this alloy is subsequently subjected to a suitable form of heat treatment, such as the preferred :one hereinafter described. In the absence of such a heat treatment, however, the hardness of the alloy continues to increase with the use of the larger amounts of copper. It is usually not feasible to add more than 3% copper because increasing the copper content above this amount'raises alloy costs by greatly increasing the difficulty in casting and fabrication of the castparts.

As a result of. the above considerations, I have found that a copper content within a preferred range of 0.3% to 1% provides excellent results in all respects.

In the alloy hereinbefore described, it is necessary that both magnesium and copper be used in conjunction to obtain the desired hardness. The use of either one of these metals alone in a quantity equal to the combined amounts of the two metals will not provide the same degree of hardness as the use of the two metals'in combination.

1 The above alloy possesses the aforementioned desirable characteristics to an outstanding degree when it consists by the absence of continuous networks of relatively brittle eutectic mixtures. Conventional alloying procedures may be employed with intermediate alloys, such as aluminumsilicon and aluminum-copper alloys, being used to introduce the silicon and copper. It is desirable that the more volatile elements, such as cadmium, be the last to be added to the melt in order to prevent their vaporization. In general, it is advisable to use the lowest temperature possible to keep the cadmium from vaporizing. For example, I have found that the aluminum, silicon and copper mayadvantageously be fused at a temperature in the order of approximately 1200 F., the melt then preferably being removed from the furnace. The magnesiumand cadmium may next be successively added to the melt, which is subsequently stirred and cast, usually in metal or graphite molds. The highest temperature suitable for casting is that point at which the cadmium just begins to vaporize or smoke. and, in order to avoid loss of metal, it is desirable not to raise the temperature of the melt above this point. Accordingly, care should be taken to prevent the temperature from exceeding approximately 1400 F. The alloy may be either cast in the desired form for use in hearings or it may be cast in ingots, rolled down to strip material of the desired thickness, and bearing liners or other bearing elements formed from the stock.

Cast articles having a metallographic structure showing a'continuous network of segregated metal compounds may be improved as to strength and fatigue resistance by suitable heat treatment. For example, I have found that a solution treatment at a temperature between approximately 900 F. and 1050 F. for a period of eight to fifteen hours is particularly effective to more completely dissolve the constituent elements and form a solid solution. Upon removing the alloy from the furnace following the solution treatment, it is preferable to cool it immediately by quenching in water. This treatment provides the alloy with the high degree of ductility, such as is desirable for rolling operations; and it may then be easily rolled down to strip material of the desired thickness.

A precipitation treatment may: thereafter be employed to substantially increase the hardness of the alloy. This process is preferably carried out by heating the article for five to ten hours at a temperature in the range between approximately 300 F. and 400 F., a precipitation treat ment at 370 F. for eight hours being particularly satisfactory. The alloy then may be again cooled, preferably in water, and suitably machined. Such a heat treating process results in an article which is three or four times as hard as it. was in the as-cast condition and whose fatigue strength is proportionally improved. 7 The specific gravity of the above-described alloy is about one-third that of a tin-bronze bearing alloy, and has much greater resistance to fatigue or to cracking under the pounding action to which bearings, such as connecting rod bearings, are subjected. This property renders such an alloy particularly suitable as a bearing for use under extremeconditions, tests on such bearings indicating the remarkable absence of wear, either of the hearing or the shaft. In addition, the alloy appears to be resistant to corrosion by acid constituents of lubricatingoils which attack many other bearing compositions.

It is to be understood that, while the invention has been described in conjunction with certain specific examples, the scope of the invention is not to be limited thereby except as defined in the appended claims.

I claim:

1. A bearing formed from a heat-treatable wrought alloy consisting of 0.05% to 3% magnesium, 0.05% to 5% cadmium, 0.3% to 5% silicon, 0.1% to 1% copper, and the balance aluminum plus incidental impurities.

2. A bearing formed of an alloy consisting essentially of 0.05% to 3% magnesium, 0.05% to 5% cadmium,

0.3% to 11% silicon, 0.1% to 5% copper, to 0.5%

iron, and the balance aluminum.

3. A bearing characterized by high anti-friction properties and resistance to distintegration under impact and to attack by acids developed in lubricating oils, said bearing being formed of an alloy consisting of 0.05 to 3% magnesium, 0.05 to cadmium, 0.3% to 5% silicon, 0.1% to 3% copper, and the balance aluminum plus incidental impurities.

4. A bearing formed of an alloy capable of being rolled into sheet form from cast ingots and having high antifriction properties and fatigue resistance, said alloy consisting essential of 0.2% to 0.5% magnesium, 0.2% to 2.5% cadmium, 2% to 5% silicon, 0.3% to 1% copper, iron not in excess of 0.5 and the balance aluminum.

References Cited in the file of this patent UNITED STATES PATENTS 1,079,035 Tebbetts Nov. 18, 1913 1,333,337 Pack et a1. Mar. 9, 1920 1,508,556 Jefr'ries et al. Sept. 16, 1924 1,572,487 Jeifries et a1. Feb. 9, 1926 1,945,297 Sterner-Rainer Jan. 30, 1934 2,026,559 Kempf et a1. Jan. 7, 1936 2,026,561 Kempf et al. Jan. 7, 1936 2,026,571 Kempf Jan. 7, 1936 2,076,281 Steudel et a1 Apr. 6, 1937 2,122,535 Nock July 5, 1938 2,214,432 Murphy et a1 Sept. 10, 1940 2,225,925 Nock Dec. 24, 1940 2,238,399 Schluchter Apr. 15, 1941 2,263,823 Bonsack Nov. 25, 1941 2,277,023 Steiner Mar. 17, 1942 2,352,990 Wood July 4, 1944 2,357,578 Brownback Sept. 5, 1944 2,435,991 Whitfield Feb. 17, 1948 2,501,440 Dix Mar. 21, 1950 2,586,099 Schultz Feb. 19, 1952 2,599,726 Schluchter June 10, 1952 FOREIGN PATENTS 534,623 Great Britain Mar. 12, 1941 550,516 Great Britain Jan. 12, 1943 OTHER REFERENCES Metal Handbook, 1948 edition, pub. by Amer. Soc. for Metals, p. 776.

Ser. No. 327,066, Garre (A. P. C.), published May Norton et a1 July 16, 1889 4, 1943,

Claims (1)

1. 4. A BEARING FORMED OF AN ALLOY CAPABLE OF BEING ROLLED INTO SHEET FORM FROM CAST INGOTS AND HAVING HIGH ANTIFRICTION PROPERTIES AND FATIGUE RESISTANCE, SAID ALLOY CONSISTING ESSENTIAL OF 0.2% TO 0.5% MAGNESIUM, 0.2% TO 2.5% CADMIUM, 2% TO 5% SILICON, 0.3% TO 1% COPPER, IRON NOT IN EXCESS OF 0.5%, AND THE BALANCE ALUMINUM.