US2763546A - Aluminum base bearing - Google Patents

Description

ALUMINUM BASE BEARING No Drawing. Application October 6, 1951, Serial No. 250,192

5 Claims. (Cl. 75147) 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 thetype disclosed in Patent No. 2,238,399, which issued Apr l 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. Accordlng ly, 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 convennonal commercial methods.

A further object of this invention is to provide such a heat treatable aluminum alloy which has exceptionally 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 difiiculty 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 containing nickel, magnesium, cadmium and silicon. Inasmuch as the alloy thus produced is a much stronger metal than the aluminum alloys heretofore used for hearing purposes, solid bearings may be made from it, no backing of steel or similar metals being necessary for many applications. Of course, this alloy also can be readily bonded to steel and many other metals and can be used on a backing.

Furthermore, the above-described alloy is characterized by much greater hardness than related aluminum base alloys heretofore used, heat treatment of this alloy resulting in increasing its hardness as much as several hundred percent. Such a high degree of hardness is desirable because recently developed high compression engines impose exceptionally heavy loads on bearings, thus creating an increased need in recent years for greater hardness in such bearings. Similarly, the greater hardness of my alloy permits it to be formed into a bearing 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 from engines after extensive use. Despite these aforementioned properties,

States Patent 0 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 4.0% nickel and the balance substantially all aluminum. Various incidental impurities may be included 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. Similarly, resistance to cracking or crumbling is also extraordinary.

The magnesium is added to increase the hardness of the bearing alloy, a magnesium content of only 0.05% being sufficient to provide a sufiicient 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 mag nesium be added in amount-s equal to at least 0.2% of the weight of the alloy. Magnesium has an adverse 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, the addition of nickel 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.

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 loss of strength. In fact, the resultant alloy is remarkably resistant to disintegration under impact or pounding such as occurs in severe bearing service. Moreover, the presence of cadmium does not effect the hardness if the alloy is subsequently heat treated. Although the affect of cadmium on both strength and hardness is negligible in any event 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.

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, a too high cadmium content raises the cost of the alloy by increasing personnel expenses because of increased handling costs and the necessity of more detailed and careful 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 in score properties if cadmium is added in quantities up to 2.5%, but increasing the cadmium content beyond this amount does not appreciably increase the score resistance of the alloy. Hence, cadmium preferably should be present in an oneness amount ranging from approximately 0.2% to 2.5% in order to providethe most desirable anti-friction proprties. 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 offset this tendency for volatilization. A cadmium content of at least 0.05% is necessary in all instances to provide adequate score resistance.

The inclusion of silicon in my aluminum base bearing alloy also enhances its score 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 thatthe 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 silicon content improves score resistance, the addition of silicon in amounts greater than 5.0% provides only slight additional beneficial properties in this respect. Accordingly, best results are obtained for most purposes when the silicon content is kept within a preferred range of 2.0% to 5.0%.

The inclusion of nickel, in combination with the magnesium addition, confers greater hardness on the aluminum base alloy. Moreover, nickel is also particularly beneficial in that it improves the score properties of the alloy by tending to counteract the detrimental effects of magnesium on score resistance. These desirable qualities with respect to hardness and score resistance are provided by adding nickel in amounts ranging from approximately 0.1% to 4.0%.

While the hardness of the alloy will be substantially reduced if the nickel content is too low, the addition of nickel' in amounts greater than 4.0% does not appreciably increase the hardness but, on the other hand, reduces the ductility of the resultant alloy, a high ductility being necessary in wrought alloys. At the same time, the score resistance of the alloy is improved only slightly if the nickel content is beyond 4.0%. Furthermore, it is generally not feasible to add more than 4.0% nickel because increasing the nickel content above this amount raises the alloy costs by greatly increasing the difficulty in casting and fabrication of the cast parts. Also too high a temperature is required to place and hold greater amounts of nickel in solution in the liquid state. inasmuch as cadmium volatilizes excessively above approximately 1400" R, a 4.0% nickel content is therefore about the upper limit that can be used with conventional foundry equipment, this being the saturation point of the nickel in the aluminum alloy at this temperature. Below this amount, however, nickel does not segregate out.

As a result of the above considerations, I have found that a nickel content within a preferred range of 0.3% to 1.5% provides excellent results in all respects.

In the alloy hereinbefore described, it is necessary that both magnesium and. nickel 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.

The above alloy possesses the aforementioned desirable characteristics to an outstanding degree when it consists of the following preferred composition: 0.5% magnesium, 2.0% cadmium, 4.0% silicon, 0.5% nickel and the balance substantially all aluminum. As hereinbefore stated, other incidental impurities may be presentin the above alloy, but for best results the amounts of these other ele ments' should be confined to relatively low proportions.

Accordingly, it is desirable that iron, for example, be present in amounts not greater than 0.5%.

In order to obtain the high degree of resistance to pounding, such as is encountered in a bearing, 1t is preferable that the alloy have a physical structure typified by the absence of continuous networks of metallic elements. Convtntional alloying procedures may be employed with intermediate alloys, such as aluminum-silicon and aluminum'nickel alloys, being used to introduce the silicon and nickel. It is desirable that the more volatile elements, such as the magnesium and 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 nickel may advantageously be fused at a temperature in the order of approximately 1200" F., the melt then preferably being removed from the furnace. The magnesium and cadmium may next be successively added to the melt, which is subsequently stirred and cast, usually in metal or graphite molds. The highest tem perature 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 not to permit the temperature to exceed approximately 1400 F. The alloy may be either cast in the desired form for use in bearings or it may be cast into 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 resistanceby suitable heat treatment. For example, I have found that a solution treatment at a temperature between approximately 900 F. and 950 F. for a period of twelve to fifteen hours is particularly eflective to more completely dissolve the constituent elements and form a solid solution. Upon removal from the furnace following the solutoin treatment, it is preferable to immediately cool the alloy by quenching it in water. This treatment provides the alloy with a 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 atemperature in the range between approximately 350 F. and 400 F., a precipitation treatment at 370 F. for eight hours being particularly satis factory. 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.

The specific gravity of the above-described alloy is about one-third that of a tin-bronze bearing alloy, and

the former 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 extreme conditions, tests on such bearings indicating the remarkable absence of wear, either of the bearing or the shaft. In addition, the alloy appears to be resistant to corrosion by acid constituents of lubricating oils 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 of a hardenable alloy characterized by high score resistance consisting essentially 'of excess of 0.5% and the balance aluminum plus incidental impurities.

2. A bearing formed of an alloy consisting essentially of from 0.05% to 3% magnesium, 0.05% to 5% cadmium, 0.3% to 11% silicon, 0.1% to 4% nickel, to 0.5 iron and the balance aluminum.

3. A bearing characterized by high anti-friction properties and resistance to disintegration 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 11% silicon, 0.1% to 4% nickel, and the balance aluminum plus incidental impurities.

4. A hearing formed of an alloy capable of being rolled into sheet form from cast ingots and having high anti-friction properties and fatigue resistance, said alloy consisting of 0.2% to 0.5% magnesium, 0.2% to 2.5% cadmium, 2% to 5% silicon, 0.3% to 1.5% nickel and the balance aluminum.

5. A heat-treated and Worked, corrosion resistant hearing consisting essentially of from 0.05% to 3% magnesium, 0.05% to 5% cadmium, 0.3% to 5% silicon, 0.1% to 1.5% nickel, iron not in excess of 0.5%, and the balance aluminum.

References Cited in the file of this patent UNITED STATES PATENTS Pritchard Apr. 19, Bossha rd Feb. 28, Sterner-Rainer Jan. 30, Pacz Sept. 25, Kempf et a1 Jan. 8, Schlucter Apr. 15, Kempf et al. June 16, Bagley Nov. 2, Hensel et a1. Apr. 15,

FOREIGN PATENTS Great Britain Feb. 22, Switzerland Feb. 29, Great Britain June 2,

OTHER REFERENCES May 4, 1943.

Claims (1)

1. A BEARING FORMED OF A HARDENABLE ALLOY ALLOY CHARACTERIZED BY HIGH SCORE RESISTANCE CONSISTING ESSENTIALLY OF FROM 0.2% TO 0.5% MAGNESIUM, 0.2% TO 2.5% CADMIUM, 2% TO 5% SILICON, 0.3% TO 1.5% NICKEL, IRON NOT IN EXCESS OF 0.5% AND THE BALANCE ALUMINUM PLUS INCIDENTAL IMPURITIES.