Electrochemical corrosion behaviour of Sn-8Zn-3Bi-XCr solder in 3.5% NaCl

This paper has explored the using of Cr micro-alloying method to enhance the corrosion resistance of Sn-Zn-Bi alloy. In addition, the influence of long-term aging on solder corrosion resistance has been studied. The electrochemical corrosion behaviour of Sn-8Zn-3Bi-XCr solder in 3.5% NaCl solution was investigated by using potentiodynamic polarization methods, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray an X-RAY diffractometer (XRD) analysis. The results obtained from polarization study show that: adding a small amount of Cr can improve the corrosion resistance of Sn-Zn-Bi alloy. It shifted the corrosion potential towards more noble values. This change was also reflected in the current density of solder alloy in passivation, corrosion rate, respectively. The oxides of zinc were responsible for the formation of passive film. Presence of Cr atoms in the oxide layer also improved the passivation behaviour of solders to a certain extent and the Sn-9Zn-3Bi-0.5Cr has the best resistance property. We can see from the SEM that it has proportional passive film. Long-term aging decreases the corrosion resistance property and it became poorer with prolonging the aging time. However, it is also more difficult to form passive film.