A texture and microstructure analysis of high speed rolling of AZ31 using split Hopkinson pressure bar results

Abstract

This study used very high strain rate uniaxial compression testing to analyze the microstructure and texture evolution during high speed rolling of as-cast AZ31B alloy. A split Hopkinson pressure bar equipped with induction radiation furnace was used to attain a strain rate of 1200 s -1 in the temperature range of 25-350 C and the result was compared with low strain rate (0.01 s -1 ) behavior. As well, high speed rolling at 500 m min -1 was employed to successfully roll AZ31 alloy in one pass with 71 % reduction at 200 C. During rolling, the mill was suddenly stopped and the sheet was withdrawn from rolling gap and the microstructure and texture evolution was observed. Grain boundary misorientation analysis shows that coincident site lattice boundaries related to contraction twins and secondary twins are more numerous in the samples deformed at high strain rate. With increasing strain for both rolling and compression at 200 C, the splitting of basal poles was observed, indicating the activation of more contraction twins and secondary twins compared to low strain rate deformation. Also, the recrystallized volume fraction increased significantly with strain rate, probably due to increasing the twin-induced recrystallization frac- tion. On annealing of the samples compressed at 200 C, secondary twins and their vicinity were observed to be the preferential sites for nucleation and it seems that rapid recrystallization on secondary twins contributes to the basal texture weakening. Therefore, an increasing number of such twins increase the texture weakening.