Microstructures And Mechanical Properties Of SiC Particulate Reinforced Magnesium Matrix Composite

The SiCp/AZ91 magnesium matrix composite, i.e. AZ91 magnesium alloy reinforced by SiC particulates with average sizes of 2 μm, has been fabricated using fluxless casting technique. Mechanical properties of the SiCp/AZ91 composite at different temperatures and under various hot processed conditions including as-cast, solution treatment, solution plus aging treatment, hot-extrusion were determined. Microstructures of the SiCp/AZ91 composite with different hot processed statuses were observed. Analysis on the tensile fracture surfaces and phase constituent of the SiCp/AZ91 composite was performed by scanning electron microscope and x-ray diffraction technique. Subsequently, the change in grain size and precipitate of the AZ91 matrix alloy as well as the distribution of reinforcing particulates in the matrix were studied. The particulate reinforcing and wear-resistant mechanism as well as tensile fracture behavior in the SiCp/AZ91 magnesium matrix composite was investigated and discussed.The observations on the microstructures showed that the addition of SiC particulates could considerably refine the grains in the AZ91 alloy matrix, and the distribution of the SiC particulates in the matrix was very homogenous. It was found that both ultimate tensile and yield strengths of as-cast SiCp/AZ91 composite at different testing temperatures were higher than those of as-cast AZ91 matrix alloy. There are two kinds of strengthening mechanism in particulate reinforcing magnesium composites. One is refinement of matrix grains caused by both heterogeneous nucleation of a-Mg phase on the surface of the SiC particulates and prohibited growth of a-Mg grains. The other is the increased dislocation density in the matrix. Heat treatment could enhance both ultimate tensile and yield strengths of the SiCp/AZ91 composite at different testing temperatures. The amplitude of the increase in the strength of was more significant for the SiCp/AZ91 composite subjected to the solution plus aging treatment. Hot-extrusion for the SiCp/AZ91 composite could considerably enhance its ultimate tensile and yield strengths at room and elevated temperatures, and the hot-extruded composite could remain the very high strengths. Compared with the AZ91 matrix alloy, the SiCp/AZ91 composite exhibited the better wear-resistance. In addition, the SiCp/AZ91 composite had lower fracture elongationcompared with the AZ91 matrix alloy. And the testing temperature had no significant effect on the elongation of the SiCp/AZ91 composite. Even at the testing temperature of 200°C, the fracture elongation was a little enhanced for the SiCp/AZ91 composite.At the room temperature, the cleavage plane and tearing ridge, which was usually taken as typical brittle fracture features, could be seen on the tensile fracture surfaces of the SiCp/AZ91 composite. At the elevated temperatures, however, the tensile fracture surface of the SiCp/AZ91 composite was composed of the cleavage plane, tearing ridge and dimple with small size. It implied that the SiCp/AZ91 composite showed a mixed ductile and brittle fracture feature.