Understanding the mechanisms of texture evolution in an Mg-2Zn-1Ca alloy during cold rolling and annealing

Abstract

A TD-split basal texture with two peaks highly tilted from the normal direction (ND) towards the transverse direction (TD) is usually developed in Mg-Zn-Ca plates and can effectively improve ductility and formability. In the present study, the texture evolution during cold rolling and subsequent annealing of a Mg-2Zn-1Ca plate with initial TD-split texture was investigated, and new insights into the mechanisms of texture evolution were obtained. The results show that a dumbbell-shaped basal texture transformed into an elliptical shape after 41% cold rolling. The random distribution of prismatic planes became preferred with <101¯0> largely parallel to the rolling direction (RD). Crystal plasticity simulations revealed that basal slip was the predominant deformation mode, and inclined basal poles toward the ND. The activation of other non-basal slips would retard this tendency. Prismatic slip with a relative activity of 20% to 30% preserved the pre-existing TD-split texture after a high rolling reduction of 41%. Pyramidal <c+a> slip prevented the formation of basal fiber and lead to a spreading of basal poles toward the RD mainly at strains over 29%. After full recrystallization, the elliptical TD-split basal texture became a dumbbell-shaped TD-split texture. Grain nucleation was observed at grain boundaries (GBN mechanism), within deformation twins (DTN mechanism), and near precipitates (PSN mechanism). GBN and DTN mainly developed a TD-split basal-texture. Instead of the formation of random orientations as considered previously, PSN produced a TD-split basal-texture, and the basal poles exhibited a much wider distribution with high angle of the peaks off the ND. The grains nucleated by GBN, DTN, and PSN did not exhibit preferred growth, and consequently, the texture hardly changed during subsequent grain growth.