Research On The Forming Rule And Microstructure Of AZ31 Magnesium Alloy Produced By Alternate Extrusion

Magnesium alloys offer advantages of low density,specific strength,excellent electromagnetic shielding effect,and easy recovery.Thus these materials have broad application prospects in various fields.However,their hexagonal close-packed(HCP)structures mean that these materials have limited strength and ductility at room temperature.The metal is under a strong threecompressive stress state in the extrusion process,which can give full play to its plasticity.Therefore,the extrusion process is particularly suitable for the preparation of low plasticity magnesium alloy.Energy saving and improving product performance are long-term concerns in extrusion process.Therefore,this paper proposes a novel extrusion process called alternate extrusion(AE).AE breaks through the traditional extrusion punch with the whole design concept,which uses two or more punches alternately loaded in the extrusion process.The proposed process uses split punches alternately instead of the overall structure to apply the downward load,but receives an unexpected load saving and grain refinement effect.We evaluated the reliability and superiority of this process in practical applications by conducting a simulation using finite element method(FEM),which confirmed the experimental results.The microstructure characteristics of AZ31 magnesium alloy produced by conventional extrusion(CE)and AE were investigated by electron backscattered diffraction(EBSD)and optical microscopy(OM),and the effects of the microstructures on the mechanical properties were studied across the extruded specimens.Results indicate that load value is significantly reduced,grain size is considerably refined,and tensile strength and elongation of material are improved after AE processing.The fractography shows that the fracture mode of AZ31 magnesium alloy changes from brittle to ductile.Type changes of texture and texture weakening in AEprocess are beneficial to reduce the anisotropy in the extrusion process of AZ31 magnesium alloy,which can obtain the uniform and stable plastic deformation and then improve the ability of plastic forming.Although the actual extrusion ratio decreases in AE process,additional shear forces produced by different punch-alternating loads at the interface improve microstructure and mechanical properties.Finally,the process of AZ31 magnesium alloy was optimized by the response surface method,and the reliability of the model was verified.It can be predicted that,with the gradual maturity of the process theory,it is expected to provide new ideas for the study of the new extrusion method.