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) Al_4.2Cu_3.2Zn_0.7 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=0~1) 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 (0~1 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.