Loading History Effect On The Evolution Of Anisotropy Of AZ31 Mg Alloy Under Change Loading:experiments And Constitutive Modeling

Magnesium and magnesium alloys have a wide range of applications in aerospace,automotive,3C,and military industries because of their abundant reserves,high specific strength and specific stiffness,good electromagnetic shielding,strong shock absorption and easy recovery and reuse prospects and huge application potential.However,since magnesium and magnesium alloys are densely packed hexagonal(HCP)crystal structures,strong initial texture is easily formed due to the preferred orientation of crystal grains during the forming process,resulting in strong anisotropy and good plastic deformation at room temperature.Poor high temperature performance is unstable,which greatly limits its practical application.Therefore,research on the plastic deformation mechanism of magnesium alloys is of great significance for improving its plastic deformation ability and expanding its practical application scale.At present,the research on the plastic deformation mechanism of magnesium alloys is still mainly focused on the simple stress state,but the actual forming process is mostly multi-axis or composite stress state.There is a huge error in the mechanical behavior during the actual forming process with unidirectional load.Therefore,in order to more accurately understand the deformation mechanism of magnesium alloy under complex stress,this paper studies the deformation mechanism of magnesium alloy sheet in uniaxial loading and two-step loading mode by combining experimental and simulation methods.The content and results are as follows:(1)The mechanical properties of the AZ31 magnesium alloy sheet and the evolution of the yield surface under the uniaxial tension and variable path two-step loading modes in different directions were studied.When the magnesium alloy sheet was deformed under uniaxial stress,it was found that the yield strength and tensile strength were significantly enhanced with the increase of the uniaxial stretching angle,and obvious anisotropy was observed.After pre-stress in different directions and secondary loading,it is found that the variation trend of yield strength and tensile strength is different.After calculating the initial yield surface and plastic working surface of different loading modes,the plasticity of pre-tension deformation on magnesium alloy is found.Distortionenhancement occursduring the deformation phase.(2)The effects of loading path changes on the microstructure and texture evolution of AZ31 magnesium alloy sheets were investigated.Under the uniaxial tensile stress state of the magnesium alloy sheet,the twin crystals are basically not activated,and the(0001)planes texture is enhanced.After pre-strain in different directions,the second loading was carried out,and it was found that there was a small amount of twinning inside the plate,but the twinning was not the main deformation mechanism.At the same time,the texture of different loading modes changed differently,resulting in the basal(0001)planes.The number of slip starts is different.This is the main reason for the difference in flow stress under the condition of change path loading.(3)Based on the tensile test and the crystal elastoplastic theory,the experimental results were verified by the visco-plastic self-consistent model.The results show that the simulation results are basically consistent with the experimental results.The main deformation modes of tensile deformation of magnesium alloy at room temperature are basal slip and prismatic slip slip,and pyramidal slip and twinning have not occurred.