The resistance to general corrosion of series of zinc-aluminum alloys modified with silicon and strontium

The resistance to corrosion of the series of zinc-aluminum casting alloys modified with silicon and strontium was studied in a sodium chloride solution. It was shown that general corrosion was the main form of corrosion of Zn25Al-Si-Sr alloys in the test solution. The corrosion process takes place through the anodic dissolution of the alloys, while the cathodic reaction is controlled by diffusion of oxygen in the test solution. Three different electrochemical techniques were applied to determine the corrosion current density, which is the electrochemical indicator of corrosion rate. The value of corrosion current density for each Zn25Al-Si-Sr alloy was calculated using the value of polarization resistance, obtained by electrochemical impedance spectroscopy or by linear polarization resistance technique. The value of corrosion current density was also determined directly from Tafel plots, which were recorded by linear sweep voltammetry. As the content of silicon and strontium in the tested alloys increases, the value of corrosion current density increases gradually. The results obtained by different electrochemical techniques are in good agreement.