Phase Equilibria of the Mg-Y-Zn System at 500 °C in the Mg-Rich Region

The Mg-rich phase equilibria of the Mg-Y-Zn system at 500 °C were investigated with equilibrated alloys, by means of electron probe microanalysis and x-ray diffraction. A partial isothermal section of < 34 at.% Y and < 50 at.% Zn was constructed and an extended section of < 50 at.% Y was produced by integrating our previous results in the Zn-rich region. Following the previous finding of seven ternary phases (τ 1 to τ 7 ) in the Zn-rich region, seven more ternary phases (τ 8 to τ 14 ) were found in the Mg-rich region in the present work. With the systematic composition measurement and XRD analysis, six of them (τ 8 to τ 13 ) were determined to be the so-called LPSO phases. They are very close to one another in composition and located approximately along the line of Y/Zn ratio = 4/3. τ 8 is believed to be X-Mg 12 YZn (14H), τ 9 to be Mg 10 ZnY (18R) and τ 13 to be 10H.