| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 92 === Given that plastic deformation, even failure, may occur due to vibration, in particular when the vibration frequency meets the resonant vibration of the structure, the vibration fracture resistance of the solder should be taken into consideration during alloy design. To realize the effect of alloying and microstructural characteristics on the vibration properties of the Sn-Zn-Bi system, this study aimed to explore the vibration fracture behaviors of binary Sn-xBi (x=10, 30, 58wt%) and Sn-xZn (x=7, 9, 11, 13wt%) solder alloys, as well as ternary Sn-8Zn-xBi (x=3 and 6wt%) and Sn-xZn-3Bi(x=5, 8, 11wt%).
Experimental results show that as for the Sn-xBi alloys, eutectic Sn-58Bi possesses superior damping capacity, greater vibration life under constant force conditions, but inferior vibration fracture resistance under constant initial deflection (ID) conditions. This can be ascribed to the continuous Sn/Bi interfaces, which absorb vibration energy via interphase sliding and provide convenient path for crack propagation.
Sn-9Zn has a poor damping capacity among the Sn-xZn alloys. The vibration fracture resistance under constant force conditions decreases in turn from Sn-13Zn, Sn-7Zn, Sn-11Zn to Sn-9Zn, and that under constant ID conditions in decreasing order is Sn-7Zn, Sn-9Zn, Sn-13Zn and Sn-11Zn. Fine eutectic Sn-Zn structure is difficult to deform and thus leads to low damping capacity. Interestingly, massive primary Zn contributes to increased damping capacity but causes crack initiation and quick propagation.
As for Sn-8Zn-xBi alloys, the damping capacity and vibration life under constant force conditions in the decreasing order is Sn-9Zn, Sn-8Zn-3Bi, and then Sn-8Zn-6Bi. In addition, as to the effect of Zn on the vibration properties of Sn-xZn-3Bi alloys, both the damping capacity and vibration life under constant force conditions decrease in turn from Sn-11Zn-3Bi, Sn-8Zn-3Bi to Sn-5Zn-3Bi. That is to say, Zn has positive effect while Bi shows negative effect to the aforementioned properties. Notably, the main crack of the Sn-5Zn-3Bi tends to propagate along the phase boundaries between proeutectic Sn and Sn-Zn eutectics.
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