Mechanical Property and Electrochemical Corrosion Behavior of Al/Sn-9Zn-XNi/Cu Joints

Al/Cu joint was widely used in the industries, such as refrigerator, cable, air condition and CPU radiator etc. Sn-9Zn-XNi lead-free solders were used to join Al and Cu in this study. Tiny Zn and coarsened Ni5Zn21 phases distributed in the Sn matrix of the bulk Sn-9Zn-XNi solders and the amount of Zn decreased while that of Ni5Zn21 phases increased with the increasing Ni addition. The wettability of Sn-9Zn-XNi solders became better on the Cu substrates but became worse on the Al substrates with the increasing Ni content in the solders. In as-soldered Al/Sn-9Zn-XNi/Cu joint, the intermetallic compound (IMC) Al4.2Cu3.2Zn0.7 layer was formed at the Sn-9Zn-XNi/Cu interface, while the Al-Zn-Sn solid solution layer was formed at the Sn-9Zn-XNi/Al interface. The Ni3Sn4 and Al3Ni mixed IMCs, which became coarser with the increasing Ni content in the solders, dispersed in the solder matrix of the Al/Sn-9Zn-XNi/Cu joint. The shear strength of the Al/Sn-9Zn-XNi/Cu (X=0 similar to 1) joints gradually decreased with the increasing Ni addition. It is considered that the coarsened Ni3Sn4 and Al3Ni IMCs would degrade the shear strength of the solder joints. With the Ni addition increased (0 similar to 1 wt%), the corrosion potentials of the Sn-9Zn-XNi bulk solders were heightened in the 5% NaCl solution and thus the corrosion resistances were improved. Adding proper content (0.25 wt.%) of Ni element in the solders would improve the corrosion resistance of Al/Sn-9Zn-XNi/Cu joints.