Experimental And Crystal Plasticity Analysis On The Deformation Mechanisms And Forming Limit Of AZ31B Mg Alloy Sheet At Warm Conditions

Magnesium alloy,as the lightest structural metal material with multiple advantages,such as high strength/stiffness to weight ratio,high heat conduction,vibration resistance,electromagnetism isolation,easy recycling,has become one of the most important materials for aerospace industries,automotive,communication and defense.Plastic deformation of Mg alloy sheet can manufacture products with higher mechanical properties.However,the application of Mg alloy sheet is quite limited due to the poor formability at room temperature,complex deformation mechanisms and lackness of suitable deformation theory.Therefore,it is of great importance to study the Mg alloy sheet with experiment and simulation and explore the correlation between deformation mechanisms and material properties.In current work,the research on AZ31B Mg alloy sheet is performed with experiment and simulation with crystal plasticity to analyze the evolution of deformation mechanisms and their effects on material properties.The main work includes four parts as following:1.Uniaxial deformation tests on AZ31B sheet at warm conditionsUniaxial tension/compression tests are performed at 100~300~oC and various conditions,and the effects of deformation condtion on mechanical properties and anisotropy are analyzed.The microstructure and texture evolution with deformation condition are analyzed by optical observation,X-ray diffraction(XRD),and electron backscattered diffraction(EBSD).Abnormal evolution in r-value and microbands are observed in the deformation and the generation conditions for these phenomena are confirmed.2.Analysis on the deformation mechanisms evolution of AZ31B sheet based on simulation with polycrystal plasticityThe deformations under 100~200~oC and 0~0.2 strain are simulated with Visco-Plastic Self-Consistent model(VPSC).The evolutions of various deformation mechanisms including,slip and twinning are analyzed with the model.Based on the effects of deformation mechanisms on grain orientation evolution,the influences of deformation mechanisms on mechanical properties and texture evolution are studied.Loading modes determine the dominant deformation mechanisms while their evolutions are affected by temperature and deformation strain.The abnormal evolution in r-value is correlated with the evolutions of prismatic<a>and basal<a>slip.3.Modelling of AZ31B sheet deformation by combining polycrystal plasticity model coupled with DRX theoryA new model(VPSC-DRX)combined DRX theory and crystal plasticity is developed by introducing the dislocation density hardening larw to analyze the high temperature deformation.The crystal deformation modes,crystal structure and grain population are cooperated with new grain generation and growth in the DRX simulation.The model is applied to the simulation of AZ31B sheet and study the effect of deformation mechanism,texture and grain size evolution.The effects of DRX on deformation mechanisms vary with loading modes.Although it will not change the dominant mechanisms,the activity ratios are significantly affected and the final texture strength is reduced.The activity of basal<a>leads to a higher evolution rate of misorientation along the compression direction and therefore the generation of micro bands.4.Formability experiment of AZ31B sheet at warm conditions and analysis with VPSC-DRX modelThe effects of deformation conditions on the formability and microstructure of AZ31B sheet are evaluated with dome stretch test at various conditons.A new method including DRX effect for forming limit diagram(FLD)calculation is proposed by combining VPSC-DRX model with Marciniak-Kuczynski(MK)theory.A modified imperfection evolution function is developed by considering the effect of DRX.With current method the effects of various deformation modes activities on the formability of the Mg sheet are studied and the influence of DRX on the formability is investigated.DRX can slow down the evolution of imperfection and the generation of new DRX grain reduce the activity of<c+a>which can improve the formability of AZ31B sheet.