Experimental investigation on the phase equilibria of the Mg-Sn-Ag system in the Mg-rich corner

Phase equilibria of the Mg-Sn-Ag system in Mg-rich corner at 320 and 400 °C were experimentally investigated with nine ternary alloys subjected to electron probe microanalysis and X-ray diffraction techniques. No ternary compounds were observed at both isothermal sections. Two three-phase triangles, i.e. hcp (Mg) + Mg2Sn + Mg3Ag and Mg2Sn + Mg3Ag + MgAg (bcc_B2), were both observed at 320 and 400 °C. A new three-phase region of Ag3Sn + Mg2Sn + MgAg (bcc_B2) was additionally observed at 320 °C, which implied that the binary phase Ag3Sn has a considerable solubility of Mg in the ternary system at the temperature. And the maximal solubility of Mg in Ag3Sn was measured to be 27.2 at.%. This result is not consistent with the thermodynamic calculated isothermal section at 350 °C from Wang et al. [11] and put forward a new requirement or refinement for the optimization of the Mg-Sn-Ag ternary system. At 400 °C, the maximal solubility of Sn in the Mg3Ag phase was determined to be about 3.0 at.% Sn, and the solubility of Ag in Mg2Sn was negligible. The temperature of ternary eutectic reaction at Mg-rich corner (L↔hcp (Mg) + Mg54Ag17 + Mg2Sn) was measured by differential scanning calorimetry. The partial isothermal sections in Mg-rich corner of the ternary system at 320 and 400 °C were then constructed based on the above experimental data.