Dual particle size (DPS) composites: effect on wear and mechanical properties of particulate metal matrix composites

Al-Si-Mg alloy composites reinforced with up to 15 vol. % of SiC particles were prepared by the melt-stirring process. The wear behavior, under low loads, of the unreinforced Al-Si-Mg alloy and the metal matrix composites (MMCs) was investigated using a ball-on-disc test at room temperature under dry conditions. Tt was found that the maximum effective increase in wear resistance (ratio of percentage reduction in weight loss and volume percent of SiC added to achieve the reduction) occurred for the composite with about 7 vol. % SiC. Metallographic investigations have revealed that the wear zone of the unreinforced alloy consisted of a hardened layer, in which fragmented Si phase was observed to be redistributed and aligned parallel to the wear direction. The delamination of material from the hardened layer was responsible for higher wear loss observed in the unreinforced alloy The thickness of the hardened layer formed on the MMC specimens (10-30 mum as against 30-60 mum in the unreinforced specimens) was reduced by the fragmentation of the incorporated SiC particles. The fragmentation of Si phase was also found to be of much lesser magnitude in the MMC specimens. This led to lesser wear in the case of the MMC specimens. It is proposed that an effective method of optimizing the wear resistance and mechanical properties of low volume fraction composites is to incorporate small and large SiC particle sizes (DPS) within the same composite. The improvement in wear resistance of the DPS composites could be attributed to the ability of the larger SiC particles to carry a greater portion of the applied load, as well as to the function of the larger SiC particles in protecting the smaller SiC particles from being gouged out during the wear process. Furthermore, the incorporation of larger particles increased the charpy impact energy of the DPS composites with respect to the composite with fully small sized particles. (C) 2001 Elsevier Science B.V. All rights reserved.