This work investigates the characteristics of vibration fatigue under a resonant state for different aging conditions, and the microstructural variation of Pb-Sn solder alloys. The major experimental parameters include natural aging time and Pb-Sn composition. Examination of crack initiation and major crack formation behavior during a resonant vibration test shows that cracks initiated at different sites of the Sn-Pb and Sn-Sn phase boundary on the specimen's surface, and that some cracks then linked up with each other to form a major crack that grew into the specimen. It is worth noticing that a stratum-type deformation occurred in the Pb-rich phase during the vibration deformation process because of the high frequency fatigue deformation of Pb-Sn eutectic alloys. In addition, coarsening was found to develop with natural aging time, and a decrease in deflection amplitude occurred during vibration tests. The investigation used heat treatment to provide further insight into the coarsening effect on the resonant fracture resistance of Pb-Sn alloys. In addition, as greater Sn content increased the fraction of the Sn-rich phase, it definitely improved vibration fracture resistance.
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