Effect of zinc content on microstructural evolution and electrification-fusion-induced failure mechanism of Sn-xZn alloys

Microstructural features of Sn-xZn alloys with varying Zn content of 7, 9, 20, 30 mass% on the electrification-fusion phenomenon were investigated in this study. Experimental results showed that the critical fusion current density (CFCD) of Sn-xZn alloys increased with increasing Zn content. The enrichment of Zn-rich phase was the main factor in the improvement of electrical conductivity and the required electrical current density for triggering microstructural evolution for the hypereutectic Sn-30Zn alloy was much higher than the hypoeutectic Sn-7Zn alloy. There is an obvious difference in the increase rate of CFCD from the hypoeutectic composition (Sn-7Zn) to the eutectic composition (Sn-9Zn) due to the microstructural evolution with increasing Zn content. Through the in-situ examination of microstructural evolution during electrificationfusion tests, the initial site of electrification-fusion-induced failure was significantly emerged from the Sn/Zn eutectic phase for both the hypoeutectic composition (Sn-7Zn) and the hypereutectic composition (Sn-30Zn). The fusion behavior of Sn-7Zn was dominated by double massive fusion regions on Sn/Zn eutectic phase and β-Sn phase, whereas the fusion behavior of Sn-30Zn was dominated by massive fusion regions only on Sn/Zn eutectic phase.