AbstractIn the light of recent changes made to the phase diagrams of the Au–Sn and Au–Pb binary systems, the constitution of the Au–AuSn–Pb partial ternary system has been redetermined using thermal analysis, metallography, and X-ray techniques. The equilibria consist of four ternary transition reactions at 63·5Au–26·0Pb–10·5Sn, 382·5°C; 42·5Au–47·5Pb–10·0Sn, 254°C; 30·5Au–60·5Pb–9·0Sn, 224°C; and 20·5Au–75·5Pb–4·0Sn, 214°C; a ternary eutectic equilibrium at 15·0Au–84·0Pb–1·0Sn, 211°C; and a four-phase monotectic equilibrium at 64·0Au–9·0Pb–27·0Sn, 257·5°C (compositions are given in atomic per cent). The phase assemblage of the partial ternary system is characterized by a region of true ternary liquid immiscibility that covers much of the composition triangle. The composition of the second liquid phase at the monotectic reaction temperature is 45·0Au–40·0Pb–15·0Sn. Solid solubilities were not determined.MST/620