Ternary compounds and phase equilibria at 320 °C of the Mg–Zn–La system in the region below 50 at%La

Abstract

Accurate phase diagrams are indispensable to boost the development of novel magnesium alloys. Up to now, however, there are still tremendous uncertainties about the number of the stable ternary compounds and related phase relationships in the Mg–Zn–La system. The Mg–Zn–La phase diagram at 320 °C in the region of <50 at% La was investigated by using 45 equilibrated alloys. Ten ternary compounds (labeled as τ₁ to τ₁₀) were found and their homogeneity ranges were measured. Two of the ternary compounds, i.e. τ₁ (space group Cmc2₁) and τ₈ (space group Immm), are identified to be the reported τ₁-La(Mg,Zn)₁₁ and La₃(Mg,Zn)₁₁ in literature, respectively. The remaining eight ternary compounds (τ₂ to τ₇, τ₉ and τ₁₀) are newly found in the present work. The lattice parameters for five of the ternary compounds (τ₁ to τ₃, τ₆ and τ₈) were calculated with the Jade 6.5 software, based on the XRD patterns. The LaMg₂ phase was found at 320 °C and could be tentatively considered as a stabilized ternary phase with the third elements. Both the τ₉ and τ₁₀, which are in phase equilibrium with the (Mg) matrix and very close to the Mg-Zn side, are expected to act as important strengthening phases in the Mg-Zn based alloys.