Grinding of alumina/aluminum composites

With the anticipated widespread usage of metal matrix composites (MMCs) in the near future, the machinability of high performance MMCs needs to be understood. This paper reports research results obtained from the grinding of aluminum-based MMCs reinforced with Al2O3 particles using grinding wheels having SiC in a vitrified matrix and diamond in a resin-bonded matrix. The issues discussed are surface roughness, grinding force, type and size of the abrasives, grinding conditions, and the consequential sub-surface integrity. The study used grinding speeds of 1100–2200 m/min, a grinding depth of 15 μm for rough grinding and 1 μm for fine grinding, and cross-feeds of 3 and 1 mm for rough and fine grinding respectively, while maintaining a constant table feed-rate of 20.8 m/min. The surface integrity of the ground surfaces and sub-surfaces were analyzed using a scanning electron microscope (SEM) and a profilometer. The surface finish values, Ra, were scattered in the range 0.15–0.70 μm for the rough-ground samples, whilst a narrower range of 0.20–0.35 μm was achieved for the fine-ground samples. Smearing of aluminum on the ground surfaces was seen for rough grinding, but was negligible for fine grinding because all the Al2O3 particles of the ground surfaces were clearly visible when observed with the SEM. Grinding using a 3000-grit diamond wheel at depth of cut of 1 μm produced many ductile streaks on the Al2O3 particles. Both the Al2O3 particles and aluminum matrix were removed by micro machining. There were no cracks and defects found on the ground surfaces. There was almost no sub-surface damage, except for a rare cracked particle being found. Rough grinding with a SiC wheel followed by fine grinding with a fine-grit diamond wheel is recommended for the grinding of alumina/aluminum composites.