Effect of processing route on texture and cold formability of AZ31 Mg alloy sheets processed by ECAP

摘要

The present work investigates the influence of different shearing patterns on mechanical and forming behavior at room temperature of equal channel angular pressing (ECAP) processed AZ31 sheets. Hot-rolled AZ31 (Mg-3Al-1Zn, wt%) sheets, with dimensions of 200 × 200 × 1.8 mm~3, were processed at 225 ℃ with channel angle of 110° regarding processing routes A, C and D. Shear deformation induced by ECAP weakens the texture and promotes a broad angular distribution of basal planes in the pressing direction on routes A and C. Especially, processing on route D makes basal planes tilted towards the rolling direction and transverse direction by 90° rotation in the sheet plane. Due to the increased activity of basal < a > slip, ECAP processed sheets exhibit the decrease in yield strength and r-value and increase in uniform strain and n-value in the pressing direction. As a result, route C has the largest uniform elongation in the rolling direction and route D provides a quasi-isotropic hardening behavior at room temperature. The improved formability of the ECAP processed sheets is attributed mainly to low r-value and high n-value. At Nakajima tests, route D provides higher forming limits than the as-rolled sample. The microstructure on route D exhibits a drastic reduction in the fraction of {10-12}-{10-11} double twins. This twinning mode leads to premature failure of the as-rolled sample under biaxial stretching. Consequently, microstructure-texture control induced by ECAP can enhance the cold formability of AZ31 sheets.