Evaluation of aluminium metal matrix composites (AA 6061 and AA 7075) for tribological applications

Abstract

In general, aluminium alloy components are light in weight and widely used in general engineering applications. But, they lack in good resistance to wear, particularly under poor, partial or boundary lubricated conditions. With solid lubricant particles dispersed in the matrix of aluminium alloy, this material exhibits good potential for resistance to wear and consequently, becomes more suitable for tribological applications. Aluminum based Metal Matrix composites (MMCs) have become a very valuable ddition to the field of newer materials for high performance tribological applications. Aluminium based composites are being increasingly used in automobiles, aerospace, marine and mineral processing industries. Aluminium matrix composites are normally processed by the liquid casting technique or powder metallurgy route. In this work, the casting was done by the liquid casting technique. The particulates were mechanically stirred and well distributed over the liquid metal, before casting and solidification. Thus, this research work aims to identify the ability of AA 6061 and AA 7075 to acquire resistance to wear, when they were cast as composites with graphite, Al2O3 and B4C as reinforcements. In all the investigations, the wear tests were conducted on pin-on-disc apparatus at room temperature. Generally, a lubricant is externally added to reduce the wear. This poses a problem when the materials need periodic applications of the lubricant, particularly to wear parts which are difficult to access. For such applications, self-lubricating materials are preferred because the solid lubricant contained in them can be automatically released during the wear process, to reduce the wear. Graphite is one of the most widely used solid lubricant materials. In this work, AA 6061 and AA 7075 are reinforced with 5, 10, 15 and 20 wt. % of graphite. The dry sliding wear of the aluminum/graphite particulate was found to decrease with graphite content and touched a minimum wear rate with 5 wt. % graphite content.