China Foundry (May 2015)
Effects of direct ultrasonic treatment on microstructure and elongation of semi-solid Sn-62Bi alloy
Abstract
A new direct ultrasonic treatment (DUT) setup with the ultrasonic horn placed in the horizontal direction was developed and used in the preparation of semi-solid Sn-62Bi slurry. The influence of DUT temperature on microstructure and properties of Sn-62Bi alloy were studied. The test results of XRD showed that the semi-solid Sn-62Bi alloy obtained by the DUT process exhibits pronounced preferential orientation of Bi (2 0 2), Bi (-1 1 1), Bi (-2 0 1), Sn (1 1 0) and Sn (2 2 0) planes. Compared to the conventional liquid casting Sn-62Bi alloy without DUT, it was discovered that the primary Bi blocks of semi-solid Sn-62Bi alloy prepared with the DUT process distribute more homogeneously and are smaller. With the treatment by ultrasonic vibration in the semi-solid state for 120 s, the higher the primary Bi phase fraction in the slurry, the smaller the size of primary semi-solid Bi blocks formed after solidification. The average side length of the primary Bi blocks was from 30 μm to 80 μm. The elongation of Sn-62Bi alloy treated by DUT for 120 s at 145 °C is 43.21%, reflecting a distinctly improvement by 129.10%, as compared to the conventional liquid casting Sn-62Bi alloy without DUT. This indicates that DUT process could improve dramatically the ductility of Sn-62Bi alloys content. The microstructure evolution mechanism of semi-solid Sn-62Bi alloy slurry was also analyzed.
