Influence of reinforcement and processing on the wear response of two magnesium alloys

Reinforcement of magnesium alloys with ceramic particulates has engineered a new family of materials that are marketed under the trade name metal-matrix composites. Rapid strides in the processing of these materials during the last two decades have provided the necessary impetus for their emergence and use in structure and automotive-related components. In this paper are reported the results of a study aimed at understanding the role of the reinforcing phase on the wear behavior of two magnesium alloys discontinuously reinforced with silicon carbide (SiC) particulates and saffil alumina short fibers. The wear rate of the reinforced magnesium alloy metal matrices is lower than that of the unreinforeed counterpart (AM60-T5 and AZ92-T6). The improved wear resistance of the composite microstructures is attributed to the presence and distribution of the ceramic reinforcement phase, which minimizes the tendency for material flow or plasticity at the surface during sliding. Wear rate is influenced by sliding speed, nature, and volume fraction of the reinforcing phase. For the unreinforced magnesium alloys, an increase in sliding speed results in a marginal increase in wear rate. For a given reinforcement (particulate and saffil fiber) in the magnesium alloy metal matrix, an increase in sliding speed had a negligible influence on wear rate. An increase in volume fraction of the reinforcing phase in the magnesium alloy metal matrix resulted in a noticeable drop in wear rate. Coefficient of friction of the unreinforced magnesium alloys AM60 and AZ92 decreased with an increase in sliding speed regardless of the amount of applied load. Addition of reinforcement, i.e., particulates and short fibers, to the magnesium alloy metal matrix resulted in a significant drop in coefficient of friction. However, increase in volume fraction of the reinforcing base in the magnesium alloy metal matrix had negligible influence on coefficient of friction. The wear characteristics of the reinforced metal matrix are discussed in light of the mutually interactive influences of intrinsic microstructural effects, strength of the microstructure, sliding speed, and local stress state.