Fabrication, Microstructure And Mechanical Properties Of AZ81 Magnesium Matrix Composites Reinforced With SiC Particles

The magnesium matrix composites, AZ81 magnesium alloy reinforced with SiC particles (average sizes are 2μm, 5μm and 10μm, respectively), have been fabricated by melt stir technique. Mechanical properties of SiCp/AZ81 composites at different temperature and heat treatment conditions were determined. Microstructure was observed to investigate changes in matrix grain size, morphology of precipitates and distribution of reinforcing particles in matrix. By means of SEM, some analysis on fracture surface and phase constituent was carried out. And reinforcing mechanism in magnesium matrix composites was discussed. Finally, the wear resistance of AZ81 magnesium matrix composites reinforced with SiC particles (average sizes are 5μm and 10μm, respectively) was measured while its wear mechanism in magnesium matrix composites was discussed.Experimental results show that SiC particles are diffused uniformly and mixed with matrix tightly by melt stir technique. After adding SiC particles which homogeneously distribute along the grain boundaries, the matrix grains are obviously refined. Among the three kinds of AZ81 magnesium matrix composites reinforced with different sizes of SiC particles, SiC particles with the size of 10μm is of great advantage to be diffused homogeneously, and which restrains theβ-Mg₁₇Al₁₂ phase forming; And solution treatment could enhance ultimate tensile strength of composites; on the contrary, reduce the yield tensile strength. The magnesium matrix composites, reinforced with relatively large size of SiC particles, which has steady mechanical properties; and SiC particles are diffused more uniformly; The mechanical properties of 10μm SiC_p/AZ81 composites are steady and excellent. Especially after solution treatment, The ultimate tensile strength of as solution SiC_p(10μm)/AZ81 is increased obviously. The ultimate tensile strength of as solution SiCp(10μm)/AZ81 at room temperature is 265.95 MPa, and increased by 31.9% compared with that of the matrix alloy. Frictional wear analyses show that furrow, plastic deformation and few spalling pit are appeared in wear surface. The main wear mechanisms are furrow and plastic deformation; besides, furrow troughs are observed. The wear resistance of SiCp/AZ81 is excellent, and due to the addition of SiC particles, which increased by 15.4% and 18.3% compared with that of the matrix alloy.Fracture surface analysis reveals that combination between matrix alloy and SiC particles is good. At low temperature, the cleavage surface and tearing ridge, which is taken as typical brittle fracture features, could be seen on fracture surfaces. With increasing test temperature, brittle features decreased, while ductile ones increased. At elevated temperatures, cleavage surface is replaced by large amount of homogeneously distributed dimples.