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 $\bar{1}$ 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.

Key words: Magnesium alloys, Rolling, Texture, Mechanical anisotropy