Effect of particle-porosity clusters on tribological behavior of cast aluminum alloy A356-SiCp metal matrix composites

Aluminum alloy composites have evoked keen interest in recent times for potential applications in aerospace and automotive industries owing to their superior strength-to-weight ratio and high-temperature strength. In the automotive industry, these materials have been evaluated for applications such as pistons, piston ring inserts, cylinder liners, brake rotors, brake pads and connecting rods. However, the extensive use of such composites is still largely unrealized due to the limited knowledge of the processing-microstructure-property relationship in such materials. In this work, cast A356-SiCp metal matrix composites with up to 15 vol.% reinforcement were produced by the melt stirring technique. The composites thus produced were evaluated for their microstructural and tribological properties. The uniformity of distribution of SiC particles (SiCp) was found to improve with increasing SiC content. Porosity was found to increase with increase in SiCp content incorporated. However, the extent of particle-porosity interaction (clustering) was observed to be greater for low SiC content composites as compared to higher SiC content composites, In sliding contact against an AISI 1060 steel counterface, it was observed that the interaction between the load on the composite specimen and the extent of particle-porosity clustering in the specimen played a significant role in determining the wear and friction behavior of the composite. For composites showing greater extent of clustering, an increase in the pressure x sliding velocity (PV) from low (0.25 MPa m s(-1)) to intermediate (0.5 MPa m s(-1)) values caused an increase in wear, while a further increase in PV value (to 0.75 MPa m s(-1)) caused a reduction in wear. On the other hand, composites, which showed lesser tendency to form particle-porosity clusters, exhibited very little change in the wear even with increasing PV values. The difference in wear behavior between the unreinforced alloy and between the various composite specimens has been attributed to the interactive effect between the particle-porosity clusters and the PV value under which wear takes place. A qualitative model, explaining the interaction between the particle-porosity clusters and the wear conditions (PV value) and its concomitant influence on wear of the material, has been proposed. (C) 2001 Elsevier Science BN. All rights reserved.