Heat treatment, microstructure and corrosion of a low-gold casting alloy

The aim of this study was to understand the relationship between heat treatment, microstructure and corrosion of a low-gold casting alloy. Potentiostatic and potentiodynamic polarization techniques were used to evaluate the chloride corrosion resistance of the alloy in the following conditions: (A) as cast, (B) bench cooled, (C) homogenized, (D) homogenized and aged for 2 h, and (E) homogenized and aged for 4 h. The microstructure of each sample, before and after corrosion, was examined by optical and/or scanning electron microscopy. In general, heterogeneous structures containing dendritic segregations and precipitates were found to be more prone to corrosion than the single phase solid solution structure produced by homogenization. On the basis of the potentiodynamic polarization data, the samples were ranked as follows: C greater than D greater than B greater than A greater than E, C being the most corrosion resistant structure.