Yasuhiro Nagatomo, Hisao Esaka and Kei Shinozuka
Department of Materials Science and Engineering, National Defense Academy of Japan, Yokosuka 239-8686
The volume fractions of primary β-Sn in Sn-Ag alloys after solidification have been measured changing the holding time in solid-liquid region. Sn-2.32 mass%Ag alloy has been used in this experiment. The specimen was cooled at a constant cooling rate of 3°C/min in Ar atmosphere from the liquid phase. After observing the recalescence by the thermocouple inserted in the crucible, the specimen was held in solid-liquid region. Changing the holding time, the volume fraction of primary β-Sn on the longitudinal cross section has been measured. The volume fraction of primary β-Sn was larger than the expected from lever rule, in case of short holding time. However, it decreased with increasing the holding time and approached to the value estimated by lever rule. Moreover, the size of primary β-Sn increased as the holding time increased. It is clear that the volume fraction of primary β-Sn depended on the holding time in solid-liquid region and it takes time to come to equilibrium. [doi:10.2320/jinstmet.JAW201306]
lead-free solder, tin-silver, β-tin, volume fraction, lever rule, holding time, solid-liquid region, equilibrium
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