Fabrication And Properties Of Particulate Reinforced Magnesium Matrix Composites

Particulate reinforced magnesium alloy matrix composites SiC_p/AZ91 and B4C_p/AZ91 were successfully fabricated by semisolid stirring method and hot-extrusion with lower porosity and harmonious particle distribution. Microstructure was observed to investigate morphology and distribution of reinforced particles in matrix by optical microscope. By means of scanning electron microscope(SEM),X-ray diffraction(XRD),energy dispersive spectrometry(EDS)and thermomechanical analysis(TMA),some analysis on fracture surface,phase constituent and thermomechanical property were carried out.The effects of fabrication parameters such as particle pretreatment, stirring speed, ceramic particle size and the rotation direction of propeller stirrer on uniformity of particles in SiC_p/AZ91 composites are researched and discussed in this paper. The experiment results indicate that semisolid stirring techniques are suitable for fabricating SiC_p/AZ91 magnesium matrix composites with reasonably uniform distribution, clean interface and lower porosity. Particle pretreatment which has significant effects on uniformity of particles can promote the wettability between matrix and particles, moreover, it can improve the distribution of particles in matrix. The distribution of particles gets harmoniously when the particle size is bigger, but it gets inharmoniously when stirring speed is lower. The rotation direction of propellerstirrer has important effect on uniformity of particles and it should use descending propellerstirrer when the particle size is under 50μm. The uniformity of particles is insensitive to the rotation direction of propellerstirrer when the particle size is bigger than 50μm and it should use ascending propellerstirrer to preventing sedimentation of particles.The experiment results indicate that the B₄C_p/AZ91 composites have a harmonious distribution and excellent properties. After hot-extrusion,the density of B4C_p/AZ91 composites is 1.873g/c³ and the linearity expansion coefficient is 19×10^-6K⁽-10 from 0 to 100℃,prosity is 0.51%,the tensile strength is 282.8MPa respectively. Hot-extrusion can significantly improve density,particle distribution and form lamellar structure which can improve the plastic propertyof composites. After hot-extrusion, it can damage the B₄C particles and form the small scale conglomerations of B₄C particles which will not impair the microstructure and properties of B₄C_p/AZ91 composites because of inflation mechanism of matrix alloy and coordinated deformation between particles and matrix. Moreover,it indicates that the higher bond strength interface is formed after hot-extrusion process by analyses of fractures. Moreover,the friction and wear properties of B₄C_p/AZ91 composites are also investigated in the paper. The results show that B₄C_p/AZ91 composites have excellent wear-resisting property compare with AZ91 alloy. The abrasion mechanism of composites is coactions of grain-abrasion and adhesion-abrasion.