| Casting-Extrusion-Shear is a combined technology of traditional extrusion and ECAE and was developed to process products with big deformation.The process is characterized by the advantages of casting and plastic deformation,while achieving the dual purpose of forming and modification.Based on previous research results and personal experience,a new type of magnesium alloy casting-extrusion-shear process and mould was designed and manufactured.This paper focused on investigating the transformation of microstructure and the room properties of AZ31 magnesium alloys after casting-extrusion-shear deformation,analyzed the effects of deformation temperature,deformation,shear angle and extrusion ratio on the microstructure and properties.Besides,simulation of whole deformation has been performed by using finite element analysis software in this paper,.The paper also discussed the influence of the temperature distribution and strain distribution of the blank on the deformation in the extrusion process,and analyzed the deformation mechanism of casting-extrusion-shear.The widely used AZ31 magnesium alloys were selected to be investigated in the experiment.By using metallographic analysis(OM)method,the microstructure and grain size of magnesium alloy extrusion were studied by observation,calculation and analysis,discuss the influence of different shear angles and different deformation temperature on the microstructure after the extrusion,room temperature tensile test and hardness test of the sample,to investigate the mechanical properties of extrusion shear forming after casting AZ31 magnesium alloy,deformation of the finite element analysis by finite element software,the temperature distribution and stress distribution were discussed in material deformation process,considering the influence of deformation process on the properties of materials.When the alloys were deformed at the temperature of 315 and 415℃,contrast the difference of microstructure between the shear angle of 30°,45°,60°,and the normal extrusion(0°).There is no crack in the extruded samples,which indicates that the as-cast AZ31 magnesium alloy has good plasticity and can be extruded directly.When the extrusion temperature was 315℃,the grain size of as cast AZ31 magnesium alloy was obviously refined and the room temperature strength and toughness were improved obviously.At 415℃,the grain size was significantly larger than that of ordinary extrusion(0°),and the mechanical properties of the composites were decreased,and the properties worse than that extruded at 315 ℃.When the extrusion was 315℃,the deformation and the degree of grain refinement were improvement with the increase of the shear angle.The recrystallization completed and the grains were coarsened when the shear angle was 60.The dendrites in cast ingot were replaced by the uniform,coarse and equiaxed grains after the cast ingot were heated at 450℃ for 3.5h,and the nonuniform composition and microstructure were removed to a great extent.Compared with the fine grains of the specimen extruded by common extrusion without shear angle,the grains of the specimens extrude with the shear angle were coarsened remarkably because of the friction and the increase of the defomation.There are obvious differences in the microstructures and properties of the different areas on ceoss section because the alloys were subjected to the unidirectional shear force during process of the extrusion-shearing,and the degree of differences amplified with the increase of the shear angleThe typical(10-10)fiber texture was characterized both in the bars subjected to the process of extrusion-shearing at 315℃ and 415℃.By contrast,the temperature of extrusion-shearing have little influence on the texture.The preferred orientation of crystals was deflected due to the shear angle.DEFORM-3D simulations show that the deformation of edge is more serious than that of the center.It mainly because of he friction between material and the mould and flow direction when deformed.The effect of temperature on the extrusion pressure is consistent with the experimental results.And the deformation of different parts of the strain point tracking analysis,simulation results and experimental results are consistent. |
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