A Study On Properties Of Mg₂B₂O_5w/ZK60 Magnesium Matrix Composites Prepared By Powder Metallurgy

Magnesium matrix composites are another kind of competitive light metal matrix composites following by aluminum matrix composites. Magnesium matrix composites are characterized by low density, high specific strength and high specific stiffness, while they also have good wear-resisting, good high-temperature resistance, good impacting resistance, excellent shock absorption properties and good dimension stability and castability, etc. Magnesium matrix composites, therefore, have wide application prospect in aerospace, military products, automobile and electronic packaging, and other fields. The magnesium borate whisker is a kind of high ratio of performance to price whisker and it also has good compatibility with Mg-based alloy. But there was little research on this whisker reinforcing magnesium alloy, so its application was limited. Therefore, in order to expand magnesium borate whisker to further application, the preparation and properties of magnesium matrix composites were studied.In this thesis, preparation and properties of the magnesium matrix composites prepared by powder metallurgy were studied. The composites were based on ZK60 alloy and reinforced with 15% volume fraction of magnesium borate whisker, and the magnesium borate whisker is cheap and also has excellent mechanical properties. Tissue and structure was studied by optical microscope, SEM, TEM, XRD, EDAX and so on. Properties were studied by universal testing machine analysis, micro hardness digital tester and so on. The result showed: Compared to composites prepared by unidirectional pressing, the density of the composites prepared by cold isostatic pressing increased by 9.52 percent on the same pressure. Compared to ZK60 alloy, the hardness of composites increased by 26.8 %. The white strip of α-Mg phase was distributed in the matrix, and the black shred of MgZn₂ phase was distributed in the grain boundary, also the same as the needle or bar of Mg₂B₂O₅ phase. Mg₂B₂O₅ whisker was well distributed in the matrix and refined grain. There was no interfacial product at the interface between Mg₂B₂O₅ whisker and ZK60 substrate. X-ray element mapping showed that there was magnesium and oxygen concentration gradient around Mg₂B₂O₅ whisker. Compared to ZK60 alloy without reinforcement, tensile strength, elasticity modulus, compressive strength, compression modulus and elongation of composites increased by 17.7 %,14.5 %,18.1%,8.3% and 1.5 % at room temperature, respectively.