THE AU-SN PHASE-DIAGRAM

The gold-rich side of the Au-Sn system has been examined using differential thermal analysis, differential scanning calorimetry and electron probe microanalysis. The presence of three intermetallic phases, beta, zeta and zeta', between gold and AuSn has been verified, although the composition ranges reported here are significantly different from those of previous studies. The resulting proposed Au-Sn phase diagram contains six intermetallic compounds and seven invariant reactions. Within the gold-rich region of the diagram there are four invariant reactions that occur: peritectics at 532 and 521-degrees-C, a eutectic at 280-degrees-C and a peritectoid at 190-degrees-C, below which zeta' is stable. The solubility range of tin in the zeta phase at 280-degrees-C is 9.5-17.6 at.% Sn and in the beta phase is 8.25-9.11 at.% Sn at the same temperature.