Mechanical And Corrosion Properties Of Mg-Zn-Y-Al Magnesium Alloys With Long-Period Stacking Ordered(LPSO) Structure

Due to the special microstructure and excellent machanical properties,Mg-Zn-Y magnesium alloys with long-period stacking ordered（LPSO）phase have attracted extensive attention in resent years.However,the mechanical properties of the present Mg-Zn-Y alloys still cannot satisfy the requirements of some high-strength in some applications.In some occasion the corrosion resistance of magnesium alloys were decreased owing to the present of the second phase.Therefore,further development and research of Mg-Zn-Y alloys with LPSOphase are necessary.Based on the related literature review,it was believed that the addition of element Al in magnesium alloy can effectively improve the mechanical and corrosion properties of Mg-Zn-Y alloys.In this paper,magnesium alloys of MgY3Zn2,MgY3Zn2Al0.5,MgY3Zn2Al and MgY3Zn2Al2 were prepared by traditional casting process.The metallographic microscope（OM）,scanning electron microscopy（SEM）,energy dispersive spectroscopy（EDS）,X-ray diffraction（XRD）and transmission electron microscopy（TEM）were used to observe the microstructures of the magnesium alloys.The mechanical properties of the alloys were characterized by tensile test.The corrosion resistance of the alloys was tested by weight loss method,hydrogen evolution method and electrochemical corrosion test method.The results showed that with the addition of Al element,the petal-like Mg₉Y₂Zn₃Al₃phase and Al₂Y phase were precipitated in the alloys.The content of LPSO phase decreases with increasing of Al content,and the morphology of LPSO phase also changed.With increasing of Al content,the tensile strength and corrosion resistance of the alloys increased first and then decreased,while the plasticity was continuely increase.The reason the addition of Al element improved the corrosion resistance of the magnesium alloy is that the solid soluted Al element inα-Mg matrix can improve the surface film integrity of the magnesium alloy.The amount of Al element solid solution inα-Mg matrix is limited.Therefore,the effect of corrosion resistance improving by Al element addition is limited.MgY3Zn2Al alloy with the best comprehensive performance of mechanical properties and corrosion resistance among the tested alloys was selected to investigate the effect of heat treatment at 400°C,430°C and 460°C for 12 hours on the mechanical properties and corrosion resistance of the alloy.It was found that with increasing of the heat treatmemt temeperatrue the amount of grain boundary LPSO phase decreased and the tensile strength and ductility of the alloy was significantly improved comparing with that of as-cast state.The reasons for the improved mechanical properties and corrosion resistance are summerized as:（1）the grain size changes after heat treatment.（2）the amount and distribution of LPSO phases are changed after heat treatment.（3）the number of Al₂Y phase is changed after heat treatment,which is affect the second phase strengthening effect.