Deformation Mechanism And Failure Behavior Of Magnesium Alloy Under High Strain Rate

Magnesium alloy is the lightest metal material which is widely used as engineeringmaterials. The static loading at room temperature for magnesium alloy properties is mainlyfocused on at present, but the mechanical properties of magnesium alloy under hightemperature and high strain rate have been studied rarely. However, the material maysuffer from impact in the real application, so it is very significant to investigate themechanical properties of magnesium alloy under high temperature and high strain rate. Inthis paper the Split Hopkinson Pressure Bar and Hopkinson Tension Bar were used toinvestigate the dynamic mechanical properties of magnesium alloy, the failure behaviorand deformation mechanism were also analysed.Dynamic compressive and tensile tests are conducted respectively on vacuum diecasting AM60B magnesium alloy and AZ31magnesium alloy welding joint (FSW jointand TIG joint) by using a Hopkinson pressure bar and Hopkinson tension bar apparatus.Applied stain rates are in the range of900s-1~4500s-1, Optical microscope and SEM areused to analyze the microstructure and fracture surface of samples after testing, thedeformation behavior strain rate sensitivity and fracture mechanism are discussed underdifferent temperature and strain rate, the dynamic compression results of vacuum diecasting AM60B magnesium alloy are simulated by using the Johnson-Cook constitutiveequation.The results show that (1) for the vacuum die casting AM60B magnesium alloy, withinthe strain range of tested, with the increasing of the strain rate, the stress-strain curvesshow rising trend and the maximum strain of AM60B magnesium alloy increased，implying that the AM60B magnesium alloy have positive strain rate effect. Thetemperature of highest deformability and fracture strength of AM60B magnesium alloy are150℃and50℃, respectively. The fracture mode of vacuum die casting AM60Bmagnesium is the mixture of ductile and cleavage fracture based on cleavage fractureunder high temperature and high strain rate. When the temperature is less than150℃, The deformation mechanism of vacuum die casting AM60B magnesium alloy is slipping underhigh stain rate compression. The constitutive equation of vacuum die casting AM60Bmagnesium alloy is built and the predicting results by JC model are consistent to testingresults.(2) For the AZ31magnesium alloy welding joint, in the process of dynamiccompression with the increasing of the strain rate, the stress-strain curves of AZ31magnesium alloy welding joint have little change, implying the stress of AZ31magnesiumalloy welding joint is not sensitive to the strain rate. The strength and plasticity of FSWjoint are better than TIG joint under high strain rate. The fracture mode of AZ31magnesium alloy welding joint is cleavage under high strain rate, but compared to TIGjoint, the FSW joint fractue are more smoothly. The deformation microstructure analysisdemonstrated that the microstructure is not sensitive to the strain rate, and the deformationmechanism of AZ31magnesium alloy welding joint is slipping under high stain ratecompression. In the process of dynamic tension, the mechanical property of FSW joint arebetter than TIG joint under similar strain rate. The fracture mode of AZ31magnesiumalloy welding joint is the mixture of ductile and cleavage fracture under high strain rate.