Investigation Of The Texture And Deformation Mechanism Of AZ31 Magnesium Alloy Produced By CVCDE

Due to the merits of low density, high specific strength, good damping, etc.,magnesium alloy has attracted much attention. However, the elongation and tensile strength of magnesium alloy are low at room temperature, so do as the corrosion resistance and the wear-resisting property. Therefore, the way of producing high performance magnesium alloy is focused by scholars and researchers. As severe plastic deformation(SPD) technique has a great grain refining capability and it can reduce internal defects of the material and improve the performance of material, it is often employed for the produce of magnesium alloy.In this paper, a new SPD technique-continuous variable cross-section direct extrusion(CVCDE) has been studied. The microstructure and properties of AZ31 magnesium alloy produced by CVCDE were researched to analyze to deformation mechanism of CVCDE.Firstly, in order to make a comparison with the microstructure and properties of AZ31 magnesium alloy produced by CVCDE and make an introduction of the research methods and theories, the microstructure and properties of extruded AZ31 magnesium alloy were studied. Results showed that the extruded AZ31 magnesium alloy showed a high yield strength, a low tensile strength and elongation. The mechanical properties of extruded AZ31 magnesium alloy were not good on the whole. Those might be caused by the large and elongated grains, nonuniform microstructure, a mass of {10-12}(86.3°<11-20>)extension twins with large size, extrusion texture with a strong intension and unhomogeneous precipitated particles in extruded AZ31 magnesium alloy. At thesame time, the number of recrystallized grains was small in extruded AZ31 magnesium alloy and most grains were deformed grains.Secondly, with the change of the mold cavity of CVCDE with 2 interim dies,three different schemes with different local strains were designed to study the microstructure and properties of AZ31 magnesium alloy produced by CVCDE with 2 interim dies. Results showed that compared with extruded AZ31 magnesium alloy, the grains of AZ31 magnesium alloy produced by CVCDE with2 interim dies were refined, and the microstructure became more uniform. At the same time, the tensile strength and elongation were obviously improved. Due to the difference in local strains, there were big differences in the microstructure and texture of CVCDEed products. In the three schemes, the types of scheme 1,scheme 2 and scheme 3 were <21-36> fiber texture, <0001>//ND fiber texture and <10-14> fiber texture, respectively. The deformation modes of the three schemes were different, in which ship and twinning were the main deformation modes in scheme 1 and scheme 2, while slip was dominant in scheme 3. The results of uniaxial tensile tests showed that the tensile strength and elongation of scheme 1 were the highest, indicating that a reasonable mold structure was benefit to the improvement of mechanical properties of AZ31 magnesium alloy.Finally, the technique of CVCDE with 3 interim dies was studied by adding the number of interim dies. At the same time, the microstructure characteristics and mechanical properties of AZ31 magnesium alloy produced by CVCDE with3 interim dies were investigated. Results showed that CVCDE with 3 interim dies could effectively refine grains, change texture type and weaken texture intensity.Comparing with extruded AZ31 magnesium alloy, recrystallization occurred in AZ31 magnesium alloy produced by CVCDE with 3 interim dies, and a narrow banded type of extension twin {10-12}(86.3°<11-20>) occurred at the same time.The equiaxed small grains, uniform microstructure and weak texture resulted in the improvement of AZ31 magnesium alloy's ductility. Compared with the strengthening effect of grain refinement, the weak basal texture and basal slip played a major role on the reduced yield strength.