Potentiodynamic polarization measurement of Sn-8.5Zn-XAI-0.5Ga alloy in 3.5% NaCl solution

The potentiodynamic polarization measurement of Sn-8.5Zn-XAl-0.5Ga alloy was carried out in 3.5% NaCl solution. The Al content in the alloy varied from 0.02-0.5 wt %. Addition of Al from 0.02 to 0.05 wt % decreased the corrosion current density and corrosion rate of the alloy. However, for Al content > 0.05 wt % a significant increase in the corrosion rate and corrosion current density was observed. These changes were also noticed in the linear polarization resistance of the alloy. Auger depth profile and secondary ion mass spectrometry results revealed that the outer surface of the passive film was primarily composed of a high concentration of gallium oxide with a low concentration of zinc oxide. Aluminum oxide and tin oxide contributed a little to the formation of the passive film on the outer surface; however, it was present in the sputtered layers. An increase in the Al content to 0.5 wt % shifted the breakdown potential toward more negative values and facilitated the increased adsorption of Cl- ion in the passive layer. The presence of Cl- ion was responsible for the breakdown of the passive film.