Fabrication and machinability of Si 3 N 4 –Mg–Al–Zn (AZ91) composites

Two Si₃N₄–Mg–Al–Zn (AZ91) metal matrix composites (MMCs) were fabricated by immersing, sintering and infiltration processes. The cutting tool materials and cutting parameter had an important influence on the lathe turning properties of Si₃N₄–Mg–Al–Zn composites. The machinability changed along with the distribution and volume fractions of reinforcement. The cutting material polycrystalline diamond (PCD) is one of the optimal materials to machine MMCs. The surface roughness of Si₃N₄–Mg–Al–Zn composites decreased with increasing cutting velocity at first, then increased with increasing cutting velocity owing to Si₃N₄ ceramic phase participating in cutting, and the surface roughness linearly increased along with the increase in feed rate of not only Mg–Al–Zn alloy but also Si₃N₄–Mg–Al–Zn composites, whereas the cutting depth had very little effect on surface roughness. The difference in machinability between Si₃N₄–Mg–Al–Zn composites and Mg–Al–Zn alloy was large.