MACHINABILITY OF CAST AND POWDER-FORMED ALUMINUM-ALLOYS REINFORCED WITH SIC PARTICLES

Metal matrix composites (MMCs) have been increasedly used in the industries because of their improved properties over those of non-reinforced allays. High hardness silicon carbide (SiC) particles are commonly used to reinforce the aluminum alloys, but the full application of such MMCs is however cost sensitive because of the high machining cost. This study investigates the machinability of cast and powder-formed aluminum alloys reinforced with SiC particles. Models for tool wear are validated, while the effect of tool materials, particle distribution, and sub-surface damage are studied and compared. Roughing with uncoated tungsten carbide inserts then finishing with polycrystalline diamond tools is the most economical route to machine SiC reinforced MMCs. The cast MMC exhibits higher machinability than that of the powder-formed MMC mainly because of the favourable shape and distribution of the particles, but weakly because of the fabricating processes. Regardless of the cutting tool materials used for machining, cracked SiC particles and debonded matrix-reinforcement interface were found underneath a machined surface. Such machine-induced defects could be a concern when using the MMCs in a critical application.