Electrochemical corrosion behaviour of Zn-Sn-Cu-xNi lead-free solder alloys

Zn-30Sn-2Cu-xNi (x=0, 0.5, 1.0, 1.5, wt.%) lead-free solder alloys were prepared via the casting method. Subsequently, their microstructures and corrosion behaviors in 0.5 mol/L NaCl solution were investigated. The electrochemical behaviour was studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques, to evaluate the influence of Ni content on the corrosion performances of the Zn-Sn-Cu alloy. The corrosion mechanism of the Zn-Sn-Cu-Ni alloys was analyzed by observing surface structure evolution during the corrosion process. The results revealed that the addition of 0.5 wt.% Ni improved the corrosion resistance of Zn-30Sn-2Cu alloy due to forming a denser and more homogeneous corrosion layer, which acted as a physical barrier. The phase identification confirmed that the main corrosion products consisted of ZnO, Zn(OH)2, and Zn5(OH)8Cl2·H2O. As the Ni content reached 1.0 and 1.5 wt.%, the corrosion resistance of Zn-30Sn-2Cu alloy declined, which could mainly be attributed to the galvanic corrosion between the (Ni, Cu)5Zn21intermetallics and Zn-rich phase, accelerating the dissolution of Zn-rich phase. Thus, Zn-30Sn-2Cu-0.5Ni solder alloy showed the best corrosion resistance.