materials Article A Study on the Effect of Ultrasonic Treatment on the Microstructure of Sn-30 wt.% Bi Alloy Shuo Wang 1,*, Jinwu Kang 1,2,*, Xiaopeng Zhang 1 and Zhipeng Guo 1 1 School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China; saviorggg@163.com ...