Effect of the Annealing Treatment on the Microstructure and Corrosion Resistance of a Cu-Al-Ni Alloy

The influence of annealing treatment on the microstructure and the corrosion behaviour of a complex bronze Al-Ni alloy was analysed. The microstructural characterization after thermic treatment shows that the retained β-phase disappears and the KII-phase undergoes a spheroidization process. Moreover, there is an augmentation of K-phase precipitates within the α-phase, particularly KIV and KV, which homogenizes the distribution of alloying elements between the phases. The corrosion behaviour was investigated by means of selective corrosion tests, potentiodynamic measurements, and electrochemical impedance spectroscopy. All of the experiments showed that thermic treatment greatly improves the corrosion resistance of the alloy. As such, annealing treatment influences a microstructure to be more dealloying resistant, which allows the development of a more protective air-formed passive film. On the other hand, the lower current registered after anodic peaks and Electrochemical Impedance Spectroscopy data seem to be correlated with a more protective layer formed on annealed material. As such, this protective character is due to a greater incorporation of Al3+, Ni2+ and Cu2+ in the passive film, as revealed by X-ray Photoelectron Spectroscopy results.