Experimental Investigation of the Mg–Zn–Zr Isothermal Section at 400 °C

Mg–Zn–Zr series Mg alloys (ZK) are one of the most important commercial Mg alloys due to their good comprehensive mechanical properties. The phase equilibria of the Mg–Zn–Zr system at 400 °C covering the overall composition range were investigated by X-ray diffraction and electron probe microanalyses on thirteen ternary alloys. Three ternary compounds, τ₁, τ₂ and τ₃, were detected to be thermodynamically stable at 400 °C, and their homogeneity range was determined to be Mg_(7–17)Zn_(80–88)Zr_(4–6), Mg_(15–22)Zn_(66–68)Zr_(9–16) and Mg₉Zn₆₈Zr₂₃ (in at.%), respectively. Eight three-phase regions and four two-phase regions were observed. The maximum solubility of Mg in Zn₂₂Zr, Zn₃₉Zr₅ and Zn₃Zr phases was measured to be 0.52, 0.37 and 0.99 at.%, respectively, while the solubility of Zr in MgZn₂ and Mg₂Zn₃ phases is negligible. The isothermal section of the Mg–Zn–Zr system at 400 °C was then constructed based on the present experimental data.