Intermetallic compound evolution and mechanical properties of Sn-0.7Cu-0.1Ni-xZn lead-free solder alloys prepared by directional solidification

The addition of Ni and Zn is known to improve the properties of Sn-0.7Cu solder. However, previous research has only focused on the improvement of Sn-0.7Cu solder performance through microalloying methods, and the impact of preparation processes and microalloying on the properties of Sn-0.7Cu solder remains unclear. In this study, Sn-0.7Cu-0.1Ni-xZn solders were prepared using the directional solidification (DS) method. DS eliminates transverse grain boundaries, making it an advantageous method to study the effect of Zn content on the mechanical properties of Sn-0.7Cu-0.1Ni solder. The results showed that some CuZn intermetallic compounds (IMCs) and Cu6Sn5 IMCs transformed into Cu5Zn8 IMCs of better mechanical properties and (Cu,Ni)6(Sn,Zn)5 IMCs of more thermodynamic stability with the increase of Zn content. The tensile results indicated that the ultimate tensile strength (UTS) and yield strength (YS) of the solders followed the same pattern as the Zn content increased. Additionally, the fracture elongation (EL) of the solders initially increased and then decreased with the increase of Zn content. The peak EL was observed at 21.9% when the Zn content was 0.5 wt%. Finally, the fracture surface analysis of the tensile specimens revealed that the solder deformation was primarily plastic, with a small degree of necking observed.