Enhanced ductility of the ZA85 magnesium alloy fabricated by equal-channel angular pressing

Equal-channel angular pressing (ECAP) was applied to the as-cast Mg–8 wt.%Zn–5 wt.%Al (ZA85) alloy to produce a fine-grained structure with fine and uniformly distributed Mg32 (Al, Zn)49 (τ-phase) particles. Experiments showed that the ZA85 alloy had an initial grain size of ∼150 μm after casting and was significantly reduced to 4 μm after six ECAP passes at 180 °C. After annealing at 300 °C for 1 h, the average grain size merely increased to 7.1 μm. This thermal stability of the fine-grained structure at temperatures at or below 325 °C is attributed to the presence of the fine and well distributed τ-phase. It was demonstrated that ECAP processing greatly enhances ductility of the experimental alloy. By testing over a range of temperatures and strain rates, a maximum elongation to failure of 400% was obtained in the ECAP ZA85 alloy tested at 300 °C (0.53 Tm) with the initial strain rate of 1.0 × 10−4 s−1. The dominant deformation mechanism for the specimens tested at 300 and 350 °C with the initial strain rates ranging from 1.0 × 10−4 s−1 to 1.0 × 10−3 s−1 is GBS controlled by grain boundary diffusion. At the higher testing temperature of 400 °C, the deformation mechanism for the experimental alloy is dislocation creep.

► The thermal stability of the ECAP ZA85 alloy is attributed to the presence of the fine and well distributed τ-phase. ► A maximum elongation of 400% was obtained at 300 °C with the strain rate of 1.0 × 10−4 s−1. ► The ECAP process greatly enhances ductility of the ZA85 alloy. ► The dominant deformation mechanism is GBS controlled by grain boundary diffusion.