Effects of PTCAP as a severe plastic deformation method on the mechanical and microstructural properties of AZ31 magnesium alloy

In this study, the effect of Parallel tubular channel angular pressing (PTCAP) as a severe plastic deformation (SPD) process on the microstructural, mechanical properties and superplasticity of AZ31 magnesium alloy were investigated. PTCAP method at 300°C was performed for production of ultra-fine grained (UFG) tube with a high superplasticity. After the first pass of PTCAP a bimodal microstructure, large gains surrounded by a large number of tiny recrystallized ones, was observed. The grain refinement and homogeneity of the microstructure increased by applying subsequent passes of PTCAP. After four pass of PTCAP, the average grain size of the material decreased from 43 µm to 6.8 µm. Vickers microhardness measurements revealed that by applying more PTCAP passes and consequently, more grain refinement, the value of hardness increased. Fractographic SEM images showed that predominately ductile fracture was occurred in all hot tensile specimens. A higher elongation to failure of 256% was achieved at a higher tensile testing temperature of 450°C and a strain rate of 10-3 1/s, due to grain boundary sliding as a dominant deformation mechanism, while this values for the as-received sample is 116% at the same tensile testing condition. Finally, it was observed that the four-pass PTCAP processed sample has higher room temperature microstructural and mechanical properties and also higher elevated temperature superplasticity than the as-received sample. Also, the grains thermal stability test was done on the four-pass PTCAP processed sample at 5 different temperatures.