Study On Structure Property And Process Of Dual-Change Channel Angle Extrusion Formed AZ31 Magnesium Alloy

Aiming at characteristic of disadvantage of magnesium's plastic deformation, the purpose of this paper is to investigate the microstructure evolution, deformation technics, and mechanical properties of AZ31 magnesium alloy by CCAE. It placed an emphasis on the understanding of grain refinement mechanism during CCAE, the mechanical properties, the extrusion force, distribution of stress and strain of simulation CCAE, in order to provide a preliminary investigation and discussion for the CCAE deformation mechanism and process.In this paper, as-casted AZ31 magnesium alloy were elected as CCAE deformation material for investigation. The AZ31 magnesium alloy microstructure and texture evolution were analyzed by Optical microscopy (OM), X-ray diffraction; the mechanical properties and fracture way and mechanism were discussed by mechanical test at room temperature, the grain refinement mechanism were explored by transmission electron microscopy (TEM), the microstructure of annealing after CCAE were discussed , the extrusion force, distribution of stress and strain during CCAE process were simulated by finite element analysis. The main results can be summarized as follows:The effect of grain refinement was improved with lowering the CCAE temperature. For AZ31 magnesium alloy, the grains were refined effectively after CCAE. The ductility, strength and microhardness were improved with the grain refinement, which is consistent with Hall-Petch relationship. In virtue of influence on texture, it contravened Hall-Petch relationship at 300℃. Both the ductility and strength mechanical properties of AZ31 magnesium alloy can be improved by CCAE.Different annealing process to AZ31 after CCAE at 250℃, annealing temperature at 350℃, and holding for 2h was the optimal annealing process. Original strip grains took place abundant recrystalliton, it arranged on equal-axis grains.Extrusion temperature was the important factor in CCAE deformation process. It was controlled easily by us. The grains become more compact and smaller, and distributed evenly. The tensile strength, yield strength and prolongation rate of magnesium alloy got improvement. When the extrusion ratio was 8.37, temperature was 250℃, the average grain size was 4.31μm, mic-hardness reached 64.3Kg/mm2, yield stress got to 171MPa, Tensile stress became to 270MPa, prolongation rate reached 19.1%, the strength and toughness of magnesium alloy could effectively improved.Grain refinement mechanism of AZ31 alloy during CCAE can be described as grain fragmentation in the shear zone and extrusion ratio zone for continuous dynamic recovery and recrystallization. By shear stress'effect, dislocation density increases and then dislocations are arranged into dislocation boundaries and sub-grain boundaries at the initial stage of CCAE deformation. When dislocation continuously moved into low angle grain, it was been nailed up interphase. So, it made the low ange grain transform to the high angle grain. With further deformation, these sub-boundaries evolve to low angle grain boundaries and high angle grain boundaries, therefore the magnesium alloy can be refined.The extrusion force and distribution of stress and strain during CCAE process were simulated by finite element software Deform-3D. Extrusion temperature was the important factor in CCAE deformation process. It controlled easily actual extrusion pressure. And the result of simulation was well agree with the experiment result, it possessed reference value for henceforth lucubrated experimentation.