Effect of texture on the mechanical properties and formability of magnesium wrought materials

With the purpose of evaluating texture hardening in magnesium alloys, the crystallographic texture and mechanical properties at room and elevated temperatures of extruded bars and rolled sheets were studied. Cast ingots were used as the reference materials, since they exhibited nearly isotropic orientation distribution. Formability of AZ31 sheet was evaluated at room and elevated temperatures by the Erichsen test, conical cup test and forming limit diagram. Strong texture is observed in magnesium wrought materials in which the basal plane is oriented parallel to the extrusion or rolling direction. As a result, tensile strength of magnesium wrought materials increased by 15 to 20% due to texture hardening at room temperature. The AZ31 alloy sheet is highly anisotropic at room temperature with high r-value above 4, resulting that forming limits in biaxial tension are much lower than those in uniaxial tension. However, this anisotropy decreases with increasing forming temperature and no texture hardening is found at 473 K. In this respect, formability of magnesium alloys sheets in terms of Erichsen and conical cup values is remarkably poor at room temperature but appreciably improves with increasing temperature. Sheet forming of magnesium alloys is practically possible only at the high temperature range where plastic anisotropy disappears.