Effect of scan rate on the corrosion performance of Sn-9Zn solder

Abstract

The corrosion behaviour of Sn-9Zn solders and the effect of corrosion properties of Sn-9Zn solders in sodium chloride (NaCl) solution were studied in open circuit potential and polarized conditions. The corrosion test was carried out with various scan rates. The Sn-9Zn firstly was melted. Next, it been pressed and punched into solder pellet shaped sample. Then, the pellet was cold-mounted with epoxy resin and hardener. The initial characterization by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) were carried out. The dissolution of Zn was identified dominating the corrosion properties of Sn-9Zn. The Sn-9Zn was polished and been soldered with the copper wire for corrosion analysis. After that, it undergoes SEM and XRD to determine secondary characterization. The microstructural analysis showed two phase morphologies presented in first characterization, while the XRD confirmed the existence phase of the samples. Besides, effect of different scan rate used was observed. By using different scan rate in potentiodynamic polarization testing, different value of corrosion potential (Ecorr) and corrosion current density (icorr) were determined. The changes of icorr indicate the corrosion is closely related with the impact of scan rated used. This analysis resulting a passivation layer that consist SnO, SnO₂, SnCl₂, SnCl₄, ZnCl₂, ZnCl₄, ZnO₂ and ZnO on the surface of the solder. Microstructural analysis after polarization shows significantly changed with the increasing of scan rate. There are coral-like structure and corrosion product were observed. As a conclusion, it showed that with these 5 scan rates (0.5, 1.0, 1.5, 2.0 and 2.5 mV/s), Sn-9Zn solder that polarise with scan rate 1.0 mV/s easy to corrode while Sn-9Zn that polarise with 2.5 mV/s hard to corrode than others.