铸态下Sn-Bi二元共晶焊料合金的组织特征及其力学性能变化.

The microstructure and mechanical properties of Sn-Bi eutectic alloys with four different Bi compositions (45%, 50%, 55%, and 60%) were studied under free solidification. The crystal growth mechanism of Sn-Bi eutectic alloys and the effect of Bi content on the microstructure of the alloy were investigated. The results showed that the microstructure of as-cast Sn-Bi eutectic alloys consists of primary solid solution phase of Sn and clusters of Sn/Bi eutectic lamellae. With increasing Bi content, the quantity of primary Sn phase with dendritic growth morphology decreased, while its size increased. A large amount of rod-like or dot-like Bi phase precipitated from the solid solution phase of primary Sn, forming a rod-like eutectic structure. In the as-cast microstructure of Sn-Bi hypereutectic alloys, it consists of primary Bi phase and clusters of Sn/Bi eutectic lamellae. The primary Bi phase does not dissolve Sn elements, and it grows in a small plate-like manner, surrounded by a layer of Sn halo phase. At room temperature, the hardness and strength of Sn-Bi eutectic alloys increase with increasing Bi content, while the elongation first increases and then decreases with increasing Bi content. [ABSTRACT FROM AUTHOR]