Structure and properties of melt-spun Zn-rich Zn-Mg alloys

Zinc together with five Zn-based alloys containing between 0.5 and 2.79 wt% Mg were rapidly solidified by melt spinning. For the alloys three kinds of microstructure were observed as-spun. Fine grained αZn equiaxed in cross section without or with Mg₂Zn₁₁ mainly along grain boundaries was found at the chill surface or just above the chill surface of the ribbon while coarser grained αZn with MgZn₂ dispersoid in the αZn matrix was present at the free side of the ribbon. Addition of 0.5 wt% Mg to pure Zn gave rise to a 20-fold decrease in αZn grain section size at the chill side of the ribbon. Further addition of Mg up to 2.8 wt% gave a more gradual decrease in αZn grain section size. It was found that solid solubility of Mg in αZn was extended to 2.8 wt% at the chill surface of the ribbon. Heat treatment above 200°C resulted in rapid precipitation and growth of Mg₂Zn₁₁ in the αZn solid solution at the chill side of the ribbons while MgZn₂ dissolved and Mg₂Zn₁₁ precipitated and grown in the αZn solid solution at the free side of the ribbons. Chill surface microhardness increased with alloy concentration and exhibited a Hall-Petch relationship with αZn grain size d according well with previous data on grain size hardening for pure Zn, Zn/ZnO and Zn-Ti-Cr.