The corrosion behaviour of Pb-free X (5Al-Zn)-YSn solders, where X is 9-50 and Y is 91-50, has been investigated with regard to open-circuit potential, galvanic corrosion and potentiodynamic polarization in a 3.5% NaCl solution. The galvanic current densities for 9(5Al-Zn)-91Sn in NaCl solution are 25, 20 and 12.5 μ.A/cm2 with respect to Cu, Ni-Cu-P and Ni-P, respectively. The corrosion behaviour has been compared with that of 63Sn-37Pb solder. A passivation behaviour is observed for all of the investigated Al-Zn-Sn solders. The magnitudes of the passivation current densities depend on the compositions of the solders and the potentials applied. The polarization behaviour of eutectic 9(5Al-Zn)-91Sn solder is very similar to that of 63Sn-37Pb solder. SnO2 is formed at polarization potentials below - 330 mV, while SnCl4 forms when the potential is at 120 mV. ZnCl2 replaces SnCl4 on polarizing at 120 mV for an extended period of 1 h.
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