Study Of Microstructure And Properties Of Magnesium Alloy By Multi-directional Deformation

The demand for magnesium alloys in the automotive industry,communications electronics industry and aerospace industry is growing.However,the close-packed hexagonal structure of magnesium alloys has poor plastic deformation and plastic workability at room temperature,which limits the application of magnesium alloys.Grain refinement is a method that can improve both plasticity and strength.Severe plastic deformation technology is one of the most effective ways to achieve grain refinement.In this paper,the principle of continuous variable section cyclic extrusion is used to study the multidirectional flexible rolling process through multidirectional cyclic extrusion deformation simulation to prepare a fine-grained magnesium alloy.Microstructure observation was performed by metallographic microscope?OM?and X-ray diffraction?XRD?.The strength,elongation and hardness are characterized by tensile test and hardness test.The friction and wear test and electrochemical corrosion test were used to analyze the wear resistance and corrosion resistance after deformation.The abrasiveness and corrosion resistance were analyzed by scanning electron microscope?SEM?on tensile fracture morphology,wear morphology and corrosion morphology.The microstructure,mechanical properties,abrasion resistance and corrosion resistance of materials during multidirectional deformation under different process parameters were analyzed.The research on the control of temperature and deformation parameters in the process of multidirectional deformation found that:The AZ31 magnesium alloy has different degrees of microstructure refinement after multi-directional deformation at different temperatures.Due to the large and uneven stress on the edges during the deformation process,intragranular slippage of coarse grains and the formation some narrow and long grains resulted in uneven distribution of the structure.With the accumulation of deformation,coarse grains are gradually broken and refined by the effect of extrusion and shearing forces.When deformed at 300?,the structure was significantly refined after one cycle of deformation,and coarse grains were broken into equiaxed crystals.With the accumulation of deformation,the grain was still refined and change little.When deformed at 250?,due to the rapid temperature loss,fractures occurred many times during deformation,and finally a uniform and refined second-cycle structure was obtained.The analysis of the mechanical properties of the material after multidirectional deformation found that:The hardness change of AZ31 magnesium alloy is corresponding to the Hall-Page formula after multi-directional deformation,and the core hardness is 92.6HV at 250?for two cycles.The tensile strength and elongation increased,but the yield strength did not change significantly.With the accumulation of deformation,the original tensile strength of room temperature increased from 329MPa to 345MPa in four cycles,and the elongation increased from 10.9%to 14.3%at 350?.After one cycle of deformation,the tensile strength increased significantly.The cumulative change in the amount of deformation is not large,the highest tensile strength of room temperature is 540MPa after four-cycle deformation,and the elongation is increased to 15.3%at 300?.The dimples gradually increased,indicating that the plasticity increased accordingly.Through the analysis of the wear resistance and corrosion resistance of the material after multidirectional deformation,it is found that the wear resistance and corrosion resistance of AZ31 magnesium alloy are improved compared with the original,the friction coefficient of the original sample is 0.209,and the multidirectional deformation sample at different temperatures.The minimum friction coefficient of the 300?three cycles deformation sample is 0.180.The original sample wear amount is 31mg.With the increase of deformation cycle,the wear amount of the three cycles deformation sample at 300?is the lowest at 23mg.The self-corrosion potential E_corrorr of the original sample was-1.530V.After the multi-directional deformation,the self-corrosion potential E_corrorr changed little,basically maintained at about-1.5V,and all moved positively.The corrosion current density icorr of the original sample was 0.4776?A,and the corrosion rate is 3.524,which is an order of magnitude lower than the original samples.