Influence of technological parameters on microstructure and mechanical properties of FSW AZ31 magnesium alloy joints

The effect of technological parameters on the temperature field, microstructure and mechanical properties of AZ31 magnesium alloy was studied by means of numerical simulation and experiments. The results of simulation show that heat generation of the joint increases correspondingly with the increase of rotate speed or the decrease of transverse velocity, and the temperature of the upper part is significantly higher than that in the lower part, which indicates that the heat generation mainly comes from the friction motion of the shoulder, while the stir pin and the plastic deformation of the material only provide a small amount of heat generation. The technological tests show the grain size of the joint decreases and the microstructure homogeneity is improved with the increase of welding speed. With the increase of rotate speed the grain size of the joint increases and the uniformity of the thermo-mechanical affected zone become worse. The rotate speed 1 400 r/min and welding speed 300 mm/min joint obtained best mechanical properties, i.e. elongation and tensile strength are 16.5% and 252 MPa, reaching 75% and 90% of the base material, respectively.