On the texture memory effect of a cross-rolled Mg-2Zn-2Gd plate after unidirectional rolling

Abstract

A Mg-2Zn-2Gd alloy subjected to a cross rolling and annealing often has a texture with c-axes of grains evenly distributing on a circle approximately 40° away from the normal direction (ND), which can completely remove the planar mechanical anisotropy. The texture memory effect and planar mechanical anisotropy of such a cross-rolled plate after an unidirectional rolling and subsequent annealing were systematically investigated. The results show that the circle-shaped texture is partially retained after the unidirectional rolling and annealing, with basal poles evenly distributing on an ellipse approximately 30°–40° away from the ND. This small texture difference will lead to quite different mechanical anisotropies between the two plates, namely, a quite low anisotropy of yield strength between the rolling direction (RD) and transverse direction (TD) before the unidirectional rolling, in contrast to an obvious mechanical anisotropy after unidirectional rolling. A quantitative calculation shows that tension along the RD of the plate after the unidirectional rolling will activate a much higher fraction of prismatic slip than tension along the TD. The much higher critical resolved shear stress for prismatic slip than that for basal slip or {10 1¯ 2} twinning accounts for the much higher yield strength of TD tension than that of RD tension. The mechanisms for texture evolution during the unidirectional rolling and annealing were also discussed.