Property improvements in fine-grained Mg-Zn-Zr alloy sheets produced by temperature-step-down multi-pass rolling

The microstructure and mechanical properties of Mg-6.63wt.%Zn-0.56wt.% Zr (ZK61) Mg alloy sheets processed by temperature-step-down multi-pass rolling were investigated. A uniform fine-grained structure with the average grain size of about 3.5 mu m, which is enriched with rod-shaped beta'(1)(MgZn2) and blocky beta'(1)(Mg2Zn3) precipitates, is attained by multiple dynamical recrystallization. An intense {0002} basal texture with a-axis randomly rotated in the plane is developed. As a consequence, a yield strength of 219 MPa, an ultimate tensile strength of 313 MPa, and a fracture elongation larger than 32% can be obtained. This enhancement in strength during rolling is mainly due to grain refinement and basal texture strengthening in the early stage, and is further contributed by precipitation hardening, simultaneously. Ductility improvement is attributed to the enhanced uniform elongation correlated with twinning suppression, and the enhanced post-necking elongation controlled by grain refinement, especially at the fine grain sizes. This can provide an essential reference for designing high-performance wrought Mg alloy sheets suitable for industrial fabrication. (C) 2015 Elsevier B.V. All rights reserved.