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

The Mg-rich phase equilibria of the Mg-Y-Zn system at 500 degrees 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 (tau(1)to tau(7)) in the Zn-rich region, seven more ternary phases (tau(8)to tau(14)) were found in the Mg-rich region in the present work. With the systematic composition measurement and XRD analysis, six of them (tau(8)to tau(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. tau(8)is believed to be X-Mg12YZn (14H), tau(9)to be Mg10ZnY (18R) and tau(13)to be 10H.