Microstructure Evolution And Mechanical Properties Of Accumulative Back Extrusion Magnesium Alloy

Magnesium alloy is the lightest metal structural material currently available for industrial applications.It has the advantages of low density(about 1.8g/cm~3),high specific strength,and high specific stiffness,and is expected to be the most promising substitute for engineering alloys.However,most of the magnesium alloys have the hexagonal closed-packed(HCP)crystal structure with low symmetry,few slip systems,and poor plastic forming ability.In addition,the bottleneck of processing and forming has largely restricted the application and development of magnesium alloy materials in a wider range.Severe plastic deformation(SPD)can effectively refine the structure and obtain a bulk material having both high strength and large plasticity by applying a large cumulative strain to the deformed material.Taking AZ91D magnesium alloy as the research object,a combination methed of theoretical analysis,numerical simulation and experiments and follows the route of homogenization treatment and hot deformation behavior of as-cast magnesium alloy?ABE finite element simulation?mold and process design?deformation process experiment?mechanical behavioral characterization of deformed alloy.The homogenization treatment and thermal deformation behavior of magnesium alloy were deeply studied by means of optical microscopy(OM),x-ray spectrometer(XRD),scanning electron microscope(SEM)and transmission electron microscopy(TEM).The as-cast AZ91D magnesium alloy constitutive model was constructed by the thermal compression simulation test,the three-dimensional thermoforming processing map reflecting the hot forming ability of the alloy was drawn,and the dynamic recrystallization kinetics prediction model was established.Combined with ABE forming finite element simulation and ABE process experimental research,it is confirmed that the ABE forming process has strong tissue refining ability.Through the characterization of ABE and hot-compression-deformed alloy under different conditions,the mechanism of grain refinement of matrix in continuous dynamic recovery recrystallization and particle stimulated nucleation and discontinuous dynamic recrystallization was revealed.The room temperature tensile test of ABE deformed alloy reveals the significant strengthening effect of ABE deformation on magnesium alloy.At the same time,it is clarified that a large number of increased grain boundaries in fine-grained magnesium alloy play an important role in the coordinated deformation.