Effect Of Heat Treatment On Dynamic Compression Behavior And Microstructure Of ZK60 Alloy

Magnesium alloys have been widely used in automotive and aerospace fields because of their low density,high specific strength and good shock absorption performance.However,in practical application,magnesium alloy auto parts may be subjected to various loads,and the mechanical properties of dynamic loading are different from those of quasi-static loading.It is widely known that the mechanical properties of ZK60 magnesium alloy are significantly improved after heat treatment.Therefore,a more comprehensive understanding of the compression properties and deformation behavior of magnesium alloys under high strain rate after different heat treatment is very important,which can provide a theoretical and practical basis for further study the high-speed deformation of magnesium alloys.The effects of aging treatment on the dynamic compression properties and microstructure evolution of extruded Mg-6Zn-0.7Zr（ZK60）alloy were studied using split Hopkinson compression bar（SHPB）equipment at different strain rates.The effect of age-precipitated phase on the deformation mechanism of ZK60 under dynamic loading was analyzed by optical microscope（OM）,electron backscatter diffraction（EBSD）,scanning electron microscope（SEM）,X-ray diffraction（XRD）and transmission electron microscope（TEM）.It provides necessary experimental data and design basis for the use of magnesium alloy auto parts under dynamic loading.The experimental results show that the microhardness of extruded ZK60 alloy increased with increasing of aging time at the aging temperature of 180℃,and reached the maximum at aging time of 16 h.Meanwhile,the amount of Mg Zn and Mg Zn₂precipitated phases gradually increased after aging treatment.The peak flow stress of the ED sample increased with increasing of aging time and strain rate,showing the positive strain rate strengthening effect,and reached the maximum at the aging time of 16 h.In addition,the peak flow stress of the ERD sample also increased with increasing of strain rate.However,the aging treatment had little effect on the peak flow stress for the ERD sample,and the alloy exhibited strong anisotropy.In addition,EBSD and TEM results show that the dynamic compression deformation mechanism of ZK60 alloy was the interaction of twins,dislocations and dynamic recrystallization.The main dynamic compression deformation mechanism of ED sample was extension twinning,supplemented by non-basal slip,and the major grain refinement mechanism was dynamic recrystallization.For the ERD sample,extension twinning was the dominant deformation mechanism,and the deformation process was coordinated by pyramidal<a>slip.In addition,the extension twinning and precipitated phases hinded the slip of dislocations,promoted the accumulation of dislocations,and improved the strength and hardness of the alloy.