The α-Mg solvus and isothermal section of Mg-rich corner in the Mg-Zn-Al ternary system at 320 °C

The phase equilibria and compositions in Mg-rich corner at 320 degrees C have been investigated in detail in the Mg-Zn-Al ternary system through the equilibrated alloy method by using X-ray diffraction (XRD), scanning electron microscopy (SEM) assisted with energy dispersive spectroscopy of X-ray (EDS). Besides the binary compounds Mg17Al12 (gamma) and MgZn in equilibrium with alpha-Mg solid solution, there exist two ternary compounds Al5Mg11Zn4 (phi) and Mg-32 (Al, Zn)(49) (tau). A new two-phase region (alpha-Mg + tau) has been experimentally identified. The whole composition region of the phi phase has been also obtained at 320 degrees C, i.e., similar to 53.7-57.0 at.% Mg, similar to 14.7-27.4 at.% Al, similar to 17.7-30.5 at.% Zn. The solubility of Al in the alpha-Mg solid solution in equilibrium with the gamma phase decreases due to the dissolution of Zn, while the solubility of Zn increases for the addition of Al when the MgZn/alpha-Mg phases are in equilibrium, compared to the Mg-Al and Mg-Zn binary systems, respectively. The maximum solubility of Zn in the gamma phase and that of Al in the MgZn phase are both about 8.3 at.% in the Mg-rich corner. Moreover, the element Al mainly substitutes the Zn in the MgZn phase while the Mg content hardly changes. (C) 2009 Elsevier B.V. All rights reserved.