Structure, texture and strength of Mg-5.8Zn-0.65Zr alloy after hot-to-warm multi-step isothermal forging and isothermal rolling to large strains

Aiming at improving deformability of wrought Mg alloys, the commercial hot-pressed alloy MA14 (ZK60) was subjected to hot/warm severe plastic deformation (SPD) to a total true strain of 9. The processing schedule involved a combination of two-stage multi-step isothermal forging performed at 400 and 300 °C and subsequent isothermal rolling at 300 °C. The evolution of microstructure, texture and mechanical properties were investigated. SPD resulted in a highly homogeneous microstructure with the size of equiaxed grain (subgrain) reduced down ~ 2.5 µm (1.5 µm). The strong initial fiber texture was transformed into the weak pyramidal texture during forging operation and then to the typical basal texture during further rolling. Changes in the distribution of excess phases are also reported. In response to microstructural changes induced by SPD, the ductility of the alloy enhanced substantially without compromising the strength. Unlike conventional semi-products having a high anisotropy of mechanical properties, the proposed processing method resulted in the isotropic yield stress and elongation to failure. The nature of grain refinement and the structure-property relations emphasizing the effects of the grain structure and texture on the tensile strength and its anisotropy are discussed.