Die structure optimization of equal channel angular extrusion for AZ31 magnesium alloy based on finite element method

Three-dimensional(3D)geometric models with different corner angles(90°and 120°)and with or without inner round fillets in the bottom die were designed.Some important process parameters were regarded as the calculation conditions used in DEFORMT M-3D software,such as stress—strain data of compression test for AZ31 magnesium,temperatures of die and billet,and friction coefficient.Influence of friction coefficient on deformation process was discussed.The results show that reasonable lubrication condition is important to plastic deformation.The change characteristics for distributions of effective stress and strain during an equal channel angular extrusion(ECAE)process with inner angle of 90°and without fillets at outer corner were described. Inhomogeneity index(C)was defined and deformation heterogeneity of ECAE was analyzed from the simulation and experiment results.The deformation homogeneity caused by fillets at outer corner increased compared with the die without fillets.The cumulated maximum strains decrease with increasing the fillets of outer corner in ECAE die and the inner corner angle.The analysis results show that better structures of ECAE die including appropriate outer corner fillet and the inner corner angle of 90°for the die can improve the strain and ensure plastic deformation homogenization to a certain extent.The required extrusion force drops with increasing the fillet made at outer corner in ECAE die.It is demonstrated that the prediction results are in good agreement with experiments and the theoretical calculation and the research conclusions in literatures.