Influence of rare earth element additions on phase transformations in the Zn−27% Al alloy

Rare earth additions of 3 wt. % were added to the Zn−27% Al−2% Cu−0.02% Mg alloy, known as ZA-27. The as-cast microstructure of this alloy consisted of two phases of supersaturated face-centered cubic β′_s and α′_s together with a hexagonal close-packed rare-earth-containing zinc-rich phase termed E phase. The phase transformations in this alloy after aging at 100 °C and 200 °C were determined. The E phase was determined to have the lattice parameters a₀ = 9.0348 Å and c₀ = 13.2194 Å, giving c₀/a₀ = 1.4632. The chemical formula of the E phase was determined to be RE₁Zn_10.9Cu_0.8. The addition of 3% rare earths into ZA-27 delayed the phase transformations of this alloy. This was caused by an increase in the aluminum content of the supersaturated β′_s phase.