ALUMINUM-TIN alloys which promise to be excellent bearing materials are the result of an intensive research and development program carried out by the authors.
After testing a number of aluminum alloys for antiscoring qualities, fatigue resistance, and mechanical stability in operation, they concluded that the optimum bearing characteristics are found in alloys having a plastic, low-melting phase and a relatively hard phase uniformly distributed throughout an aluminum solid solution matrix of moderate hardness.
Tin, affording ease in alloying and resistance to corrosion in lubricating oils, furnishes the best plastic constituent. Pure aluminum-tin alloys do not possess the strength needed in highly stressed bearings. The addition of silicon forms a hard constituent which increases strength markedly. Antiscuffing qualities are improved also, although ductility is reduced.
An aluminum-tin-silicon-copper alloy is the most successful aluminum bearing alloy yet developed, according to the authors. It was intended for permanent-mold castings, but it may be used in centrifugal castings for large-size bearings or in pressure die castings and sheet for small thin-walled bearings. Manufacturing costs are low because of good machining characteristics and the high speed with which the material can be cut and finished.