Study On Room Temperature Deformation Behavior Of AZ31 Magnesium Alloy Prepared By Friction Stir Processing

AZ31 magnesium alloy is the most widely used deformation magnesium alloy. The study on plastic deformation behavior of magnesium alloy is important. It will expand the application of the magnesium alloy.The different grain sizes of fine-grain AZ31 magnesium alloy were prepared by friction stir processing with different processing parameters in air. The microstructure and microhardness of stir zone were observed. The room-temperature uniaxial tensile experiment of magnesium alloy were testing along processing direction(PD) and transverse direction(TD). The mechanical property and microtexture of fine-grain AZ31 magnesium alloy were analyzed. The texture effect on deformation behavior of fine-grained AZ31 magnesium alloy was analyzed. The major conclusions are as follows:After friction stir processing, the average grain sizes were 1.56~5.95μm in the stir zone. The grain size increases with the increase of the stir-pin rotation speed. The microhardness increases with the decrease of the grain size. The fraction of high-angle grain boundaries was determined to be 86.2% in base material. After friction stir processing, the fraction of high-angle grain boundaries was down to 54.0%~59.9%. Normal direction of the base plane was perpendicular to PD in base material. The intensity of texture was 8.22. After friction stir processing, the direction of texture was deflect. The angle between the Normal direction of the base plane and PD direction was 60°~68°. The intensity of texture is 65.92~69.91. The relationship between grain size and yield strength conform to the Hall-Petch equation in the direction of PD and TD. The mechanical properties of magnesium alloy showed obvious anisotropy. When the grain size was unchanging and the orientation of the texture was easy to slip, the yield strength would reduce. This indicated that grain size, grain boundary orientation, texture can affect the yield strength. Specimens deformed mainly by basal slip with additional extension twinning in the PD exhibited low tensile yield strength and high degree of work hardening. Specimens deformed by non-basal slip in the TD showed high tensile yield strength and low degree of work hardening. The difference work hardening behavior in PD, TD direction resulted from the activation of extension twinning. When the orientation of the texture was easy to elicit extension twinning, the magnesium alloy could show continuous work hardening, and the plasticity of materials was increased. Texture and grain size have influence on extension twinning, and extension twinning has influence on work hardening behavior.