The Role of Macrostructural and Microstructural Morphologies on the Corrosion Resistance of Zn and a Zn-4% Al Alloy

Abstract

Different structural morphologies may develop due to a wide range of the operational conditions that may exist during casting. It is well known that corrosion resistance and mechanical properties depend on solidification structures. The aim of this study is to investigate both the influence of columnar and equiaxed structures of zinc as-cast samples and of dendritic microstructural array of a Zn-Al alloy on the corrosion resistance. In order to obtain columnar and equiaxed structures, both a vertical upward solidification apparatus and a permanent steel mold casting assembly were used. The corrosion resistance was analyzed using electrochemical impedance spectroscopy and Tafel extrapolation. Corrosion tests were conducted in a 3% (vol.) NaCl solution at room temperature. It was found that coarser macrostructures tend to provide higher corrosion resistance for both columnar and equiaxed morphologies. On the other hand, finer secondary dendrite arm spacing is conducive to a better corrosion behavior of a Zn-4% Al alloy.