Adiabatic Shear Behavior Of Two Magnesium Alloy With Different Grain Size Under High-Strain-Rate

Magnesium alloys have a wide range of application in the fields of automobiles and aerospace due to their advantages of high specific strength,high specific rigidity,and easy machining.In order to better understand its deformation behavior under high-speed deformation in actual usage,the mechanical behavior under dynamic load conditions is systematically studied.In this paper,AZ31 and ZK60 magnesium alloy with different grain sizes were prepared by extrusion shearing and different heat treatment.The high-strain-rate deformation was conducted on the prepared AZ31 and ZK60 magnesium alloy cylindrical and hat-shaped samples at different strain rates by using an split hopkinson pressure bar.The optical microscope（OM）,electron backscatter diffraction（EBSD）and transmission electron microscope（TEM）were used to observe the microstructure of the samples after high-speed deformation.The deformation mechanism and deformation behavior of AZ31 magnesium alloy and ZK60 magnesium alloy with different grain sizes at high strain rates,and the effect of grain size on the adiabatic shear behavior of AZ31 magnesium alloy and ZK60 magnesium alloy were studied.The results showed that both AZ31 and ZK60 magnesium alloy exhibited significant strain rate strengthening effects at different strain rates.The main deformation mode of 3μm AZ31magnesium alloy sample at high strain rate is pyramidal<c+a>slip,and the main deformation mode of 25μm AZ31 sample and 60μm AZ31 magnesium alloy sample at high strain rate are pyramidal<c+a>slip and{101 2}tensile twinning.With the increase of strain rate,the number of twins and the grain size are increased gradually,and when the strain rate is increased to 1900s^-1the samples were broken.The main deformation modes for ZK60 magnesium alloy at high strain rates are pyramidal<a>slip and{10 1 2}tensile twinning.Comparing AZ31 and ZK60magnesium alloy under the same grain size,it can be found that the twinning degree of ZK60magnesium alloy is significantly higher than that of AZ31 magnesium alloy,and their main sliding modes are different.AZ31 magnesium alloy is pyramidal<c+a>slip,and ZK60magnesium alloy is pyramidal<a>slip.Under forced shear loading conditions,the formation of adiabatic shear bands was observed in three sizes of AZ31 and 3μm and 25μm ZK60 magnesium alloy hat-shaped samples.Through the observation of the width of the adiabatic shear zone,microvoids,cracks,the adiabatic shear sensitivity of ZK60 magnesium alloy and AZ31 magnesium alloy increases with the increase of grain size.The microhardness of the shear band of AZ31 magnesium alloy and ZK60 magnesium alloy is significantly higher than that of the matrix.A large number of fine dynamic recrystallizations were observed in the three sizes of AZ31 magnesium alloys.After calculation,it can be inferred that these fine recrystallized grains are all formed by rotating dynamic recrystallization（RDRX）.