Influence of Thermal Treatments on the Corrosion Behaviour of Nickel-Aluminum Bronze in Freshwater-Like Aqueous Environment

Nickel-Aluminium Bronze is a copper alloy with excellent corrosion resistance in marine environments. However, there are also applications of NAB in freshwater and corrosion phenomena have been observed in such cases. To explore the effect of microstructure on the corrosion behaviour, heat treatments were applied to NAB samples, which were corrosion tested in electrolytes with a composition typical for freshwater. Depending on the presence of bicarbonate, sulfate, and chloride, different kinds of corrosion attack were observed. The mayor effect lies in minimization of the β-phase amount and increasing the portion of a- and κ-phases. Corrosion promoted by sulfate is the major hazard in fresh water, while the passivating effect of bicarbonate supports localization of the attack. Chloride plays an ambivalent role; it promotes the corrosion attack but limits the progressively penetrating evolution of localized corrosion. Since the composition of freshwater has a stronger impact on the corrosion phenomena of the NAB alloy, the influence of the heat treatments is not clearly evident. Compared to seawater, heat treatments have a lesser effect on the corrosion behaviour in freshwater.