1 Phase Transition Temperatures of Sn-Zn-Al System and their Comparison with Calculated Phase Diagrams

The Sn-Zn-Al system was studied in connection with the possible substitution of lead based solders for temperatures up to 350°C. Ternary alloys with up to 3 wt. % of aluminium were prepared. The investigated alloys lie close to the monovariant line (“eutectic valley”) of the Sn-Zn-Al system. The temperatures of phase transitions of six binary Sn-Zn reference alloys and fourteen ternary Sn-Zn-Al alloys using DTA method were investigated in this paper. DTA experiments were performed at the heating/cooling rate of 4°C min-1 using Setaram SETSYS 18TM experimental equipment. The temperatures of phase transitions in the ternary Sn-Zn-Al system were obtained, namely the temperature of ternary eutectic reaction TE1 (197.7 ± 0.7°C), temperature of ternary transition reaction TU1 (278.6 ± 0.7°C), temperatures of liquidus, and other transition temperatures for studied alloys. Temperatures obtained during DTA heating runs were used as authoritative. DTA curves obtained during cooling enabled the better differentiation of overlapped heat effects (peaks) obtained during heating. Theoretical isopleths of the Sn-Zn-Al phase diagram were calculated using the Thermocalc software and MP0602 thermodynamic database. Experimental data were compared with the calculated temperatures and good agreement was obtained