Effects of aging on structural evolution of the rapidly solidified Sn–Ag–Zn eutectic solder

The structural stability of the rapidly solidified eutectic Sn-3.7 wt.%Ag-0.9 wt.%Zn solder was explored by aging at room temperature (298 K). After aging for 2 weeks, the microstructure varied a lot in the morphology of intermetallic compounds (IMCs) in the investigated Sn–Ag–Zn solder. Dot-like Ag3Sn IMCs in the rapidly solidified solder congregated and formed bulk ones in order to minimize the system energy, which is contrary to a stable microstructure in the slowly cooled specimen. It seems that the coarsening of the IMCs in the microstructure of the rapidly solidified specimen brought a significant softening during aging of the explored Sn–Ag–Zn alloy. Furthermore, with the addition of zinc, the solder system becomes harder than the eutectic Sn–Ag system and the Ag–Zn phase dispersed in the eutectic Sn–Ag–Zn solder could strengthen the system as a reinforcing secondary phase.