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 degrees C covering the overall composition range were investigated by X-ray diffraction and electron probe microanalyses on thirteen ternary alloys. Three ternary compounds, (1), (2) and (3), were detected to be thermodynamically stable at 400 degrees 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 0.99at.%, respectively, while the solubility of Zr in MgZn2 and Mg2Zn3 phases is negligible. The isothermal section of the Mg-Zn-Zr system at 400 degrees C was then constructed based on the present experimental data.