Research On The Deformation Behavior Of Magnesium Alloy Prepared By Friction Stir Processing

In this paper, FSP AZ31 and FSP AZ80 magnesium alloy were researched. The effects of grain size, grain orientation and strain rate on the room temperature mechanical properties of FSP AZ31 magnesium alloy were studied. The effects of grain size, grain orientation on the high temperature mechanical properties of FSP AZ31 magnesium alloy were discussed. High temperature tensile tests of FSP AZ80 magnesium alloy were carried out under different temperatures and different strain rates and the superplastic deformation behavior was investigated. The main conclusions are as follows:With the increase of grain size, the tensile strength of FSP AZ31 magnesium alloy along the TD direction decreases and the elongation increases; the mechanical properties of FSP AZ31 magnesium alloy along the PD direction are nearly constant. The deformation mechanism of TD direction is cylindrical slip and the deformation mechanism of PD direction is basal slip. The tensile fracture along the TD direction shows cleavage and the tensile fracture surface along the PD direction shows a tough nest generation, thus the sample along PD direction shows good plasticity. With the increase of strain rate, the tensile strength increases but the elongation decreases. The true stress true strain curves at different strain rates are similar in shape and show the characteristics of the upper concave and the work hardening rate curve is hump shaped. At the initial stage of the deformation, the value of strain rate sensitivity exponent is negative and the value becomes positive gradually with the increase of the strain.With the increase of temperature, the strength of FSP AZ31 magnesium alloy decreased. At 350℃, the effects of grain size and grain orientation on the performance is weakened. At 300℃ and 350℃, the elongations of FSP AZ80 magnesium alloy decrease with the increase of strain rate. At 400℃, the elongation increases with the increase of strain rate. The optimal superplastic condition is that the deformation temperature is 400℃ and the strain rate is 1×10-3 s-1. The maximum elongation is 413%. The value of strain rate sensitivity exponent of optimal superplastic sample is 0.37. There are holes in the microstructure after high temperature tensile test. Fracture shows intergranular ductile fracture.