Effect of Rare Earth Y on Microstructure and Properties of Sn-58Bi Solder Alloy

Sn-58Bi-xY alloys with different Y contents (x = 0.0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% (mass fraction, the same below )) were fabricated in a vacuum furnace in nitrogen atmosphere. Microstructure, phase composition, melting characteristic, wettability and hardness of the alloys were investigated, and the influence of the rare earth Y on the formation of intermetallic compound among Sn-58Bi/Cu were analyzed, and the shear strength were test. The results show that the Sn-Bi microstructure is refined, and the microstructure of Sn-58Bi-xY is rich in Sn phase, Bi phase and eutectic microstructure of layered structure. The rare earth Y is distributed in rich Bi phase evenly. The melting points and melting ranges are less affected with the Y addition. The wettability of Sn-58Bi alloys reduces when the Y contents increase, but the hardness of Sn-58Bi alloys increases and reaches the maximum value 24.18HV when the content of Y is 0.4%. Rare earth Y can improve the shear strength of Sn-58Bi-xY/Cu solder joints, and the shear strength of the joints reach the maximum value 53.55 MPa when the content of Y is 0.2%. Y can promote the reaction of Sn-58Bi solder with Cu during welding and forming Cu6Sn5 intermetallic compound