Microstructure And Mechanical Properties Of AZ31Alloy Matrix Reinforced By Mg-Zn-Gd Quasicrystal

The Mg-Zn-Gd icosahedral quasicrystal master alloy particles was added into theAZ31alloy by the repeated plastic working (RPW) process in order to develop themechanical properties of the AZ31alloys at room and high temperature. Themicrostructure and tensile properties of composites have been investigated by usingOptical Microscope (OM), Scanning Electron Microscope (SEM), TransmissionElectron Microscopy (TEM), X-ray Diffraction (XRD), Energy Spectrum Analysis(EDS), Thermal Analyzer (DSC), Micro-hardness Tester, tensile testing machine andwear equipment.It is shown that the solidification microstructure in Mg-Zn-Gd icosahedralquasicrystal master alloy consists of the primary phase, Mg3Zn6Gd quasicrystal phasewhich is generated by the peritectic reaction, MgZn phase and-Mg solid solution inconventional solidification. the content of quasicrystal phase in Mg-Zn-Gdicosahedral quasicrystal master alloy is about70%.The results suggested that the RPW process could effectively refine the matrixand make the I-phase particles distributed well. The composites which With10wt.%content of quasi-crystal master alloy and with250cycles of RPW process had a goodtensile properties, The ultimate tensile strength (UTS) reached its maximum values of373.7.3MPa. During high temperature (175℃), when the content of I-phase particlesin composite materials reached10wt.%and15wt.%, and the RPW processincreased from250cycles to300cycles, the composite materials were increased by37.1MPa and39.9MPa. It can be seen that the tensile strength increased moreobviously, but the tensile strength of pure AZ31magnesium alloy increased by only6.2MPa.The evolution of grain size is the combination of grain refine during RPWprocessing, the dynamic recrystallization during hot extrusion. It can beinferred thathigh dislocation density is first developed in the vicinity of the boundaries of coarsegrains or the second phase’s boundary, And as deformation progresses, subgrainstructure will form over the whole volume of the grain through the conversion ofdislocation cell walls into subgrain boundaries, and finally the subgrain boundariesconverted to grain boundaries. The nucleation of dynamic recrystallization is at grainboundaries and the second phase’s boundary. In addition, the reinforcement phase hasa pinning effect for dislocation movement. They all can effectively increase mechanical properties of the composite materials.The results of wear experiment show that the composite material whichcontains15wt.%of I-phase and after250cycles of RPW process has good wearresistance. When the load reached175g, the wear volume tends to be stable.According to the experiment analysis in this study, with the addition of thequasicrystal particles, the wear resistance of composite materials were effectivelyimproved.