Effect Of Different Deformation On High Strain Rate Deformation Mechanism Of Extruded ZK60 Magnesium Alloy

Magnesium alloy is considered to be the lightest structure metal material,which have been widely applied in the aerospace,national defense and military industry,3C and other fields.Especially under the background of energy saving and emission reduction,environmental pollution reduction and automobile lightweight,magnesium alloys parts have a great application space and development potential in automobile industry.However,the close-packed hexagonal structure limits the application of plastic processing,which due to its fewer slipping systems at room temperature.Moreover,the loading that magnesium alloy parts beared is not only the static loading,but also the dynamic impact loading.For example,in the rear-end and frontal collision,the front end of automobile need to bear huge dynamic impact loading.However,the deformation degree of front end of automobile is different which is due to different collision degree.,It is easy to cause the instability of magnesium alloys parts in the process of the dynamic service and further affects the safety performance of automobile.To solve these problems,it is imperative to analyze the deformation mechanism of magnesium alloy under dynamic loading.It has practical application value and theoretical significance for the design,development,application and reliability evaluation of magnesium alloy parts.In this paper,the dynamic mechanical behavior of extruded ZK60 magnesium alloy with different deformation degrees(4%,6%,9%,12%,4%+8%,6%+6% and 9%+3%)under high strain rate dynamic load were studied by Split Hopkinson Pressure Bar(SHPB).Furthermore,the microstructure of the samples along Extension Direction(ED)and Extension Radical Direction(ERD)was investigated by X-ray Diffraction(XRD),Electron Back-Scattered Diffraction(EBSD)and Transmission Electron Microscopy(TEM).In addition,the microstructure evolution and deformation mechanism transformation in different deformation stages were investigated.The experimental results show that during primary deformation,the true stress-strain curve of the sample along ED direction is S-shaped.And the true stress-strain curve of the sample along ERD is C-shaped.During secondary deformation,the true stress-strain curve of samples along ED direction is no longer "S",but similar to the "C" shape of samples along ERD direction.The results show that,in the early stage of deformation(< 6%)with the increase of deformation,{101?2} tension twinning grows continuously by consuming matrix grains,and the dominant deformation mechanism is {101?2} tension twinning and basal slip.When the deformation amount exceeds 6%,the dominant deformation mechanism is <c+a> pyramidal slip.The dominant deformation mechanism at the initial stage of ERD direction sample deformation is basal slip.When the deformation amount is between 4% and 9%,tension twinning and compression twinning participate in coordinated deformation,and the dominant deformation mechanism from4% to fracture is <c+a> pyramidal slip.During secondary deformation,there are twinning produced in the primary deformation process in the sample along ED direction,thus the deformation of the sample is dominated by <c+a> pyramidal slip,and {101?2} tension twinning and basal slip coordinate the partial deformation;In addition,the main mechanism of secondary deformation of ERD sample is <c+a> pyramidal slip.