Microstructure evolution and mechanical performance improvement of thin ZK61 magnesium alloy sheets subjected to cumulative cold rolling and intermediate annealing

Thin ZK61 magnesium alloy sheets with ultrafine-grain structure were fabricated by cumulative cold rolling with intermediate annealing treatments. Microstructure refinement and uniformity were manifestly achieved by multiple static recrystallization during the process while planar texture anisotropy was strikingly improved as {0002} basal pole intensity in transverse direction gradually enhanced and that in rolling direction weakened. The dispersed precipitates mainly composed of blocky β1′ (Mg2Zn3 or Mg4Zn7) and globular β equilibrium phases slightly aggregated and coarsened as the process continuing. The two aforementioned factors of grain refinement and texture variation resulted in a contrary tendency in yield strength with grain size between rolling direction and transverse direction in coarse grain region but an identical increment afterwards under stable basal texture, which was well estimated following the Hall-Petch relationship with texture effect. Fracture elongation over 25% was obtained due to the enhancement of basal texture weakening to uniform elongation following εu≈78.8mbas. and that of grain refining to post-uniform elongation accounting for 40%.