Mechanical anisotropy and deep drawing behaviors of AZ31 magnesium alloy sheets produced by unidirectional and cross rolling

Magnesium AZ31 sheets were produced by rolling on the as-extruded plates with two rolling techniques: cross rolling (CR), a laboratory process wherein the rolling direction is changed by 90° after each rolling pass, and conventional unidirectional rolling (UR) wherein the rolling direction is unchanged. The microstructure and texture, tensile mechanical properties in terms of strength and elongation, and also the anisotropy of the UR and CR sheets were investigated at room temperature. As expected, the UR sheet has obvious planar anisotropy from the strong basal-type texture; however, the CR sheet shows improved ductility of 28% elongation-to-fracture and low r value close to 1 which enhances drawing capability. Deep drawing tests carried out at 150°C reveals that the UR cups show obvious earing corresponding to a large negative value of planar anisotropy Δr, while earing of the CR cups is negligible due to a positive value of Δr. Moreover, the CR sheet produces a deeper drawn cup than the UR sheet as a result of its lower normal anisotropy r¯ value and larger elongation compared with the UR sheet.