Corrosion Resistances of As-Cast and Quenched Samples of a Zn-22Al Eutectoid Alloy

To address the increasing demand for high performance and high quality die castings. Zn-Al casting alloys have been developed, in particular for applications in the automotive industry. This family of alloys has good physical, mechanical and tribological properties and is commonly used as foundry alloys in a variety of applications. Particularly, the Zn-22 wt% Al eutectoid alloy is a classic commercial material and a fine-grained structure can be obtained by using a suitable heat treatment which can induce a superplastic behavior. On the other hand, this heat treatment can affect the corrosion behavior of such alloy. The present work focuses on the influence of as-cast and quenched microstructures of the Zn-22wt%Al eutectoid alloy on its electrochemical corrosion behavior. The typical microstructural patterns were examined by using optical microscopy techniques. In order to evaluate the corrosion behavior of such alloy, corrosion tests were performed in a 0.5 M NaCl solution at 25 degrees C by using an electrochemical impedance spectroscopy (EIS) technique and potentiodynamic polarization curves. An equivalent circuit by using the ZView software was also used to provide quantitative support for the discussions and understanding of the electrochemical corrosion behavior. It was found that the heat-treated samples are more susceptible to the corrosion action than the as-cast alloy sample.