Effect of Al/SiC interface and intermetallic particles on elevated temperature corrosion of hypoeutectic Al-Si-Mg composites

The role of intermetallics and silicon carbide (SiC) particles on the corrosion behavior of Al-SiC composites has been investigated. Alloys F3K (UNS A0338) and F3S (UNS A0359) were selected for investigation. Results of weight loss and elevated-temperature electrochemical studies at different rotational and linear velocities have been presented. The results showed that alloys reinforced with SiC exhibited higher corrosion rates compared to unreinforced alloys. Al/SiC interface was the preferred site for localized corrosion and pitting was predominantly observed. The Al/SiC interface was more densely populated with secondary-phase particles than the matrix, and the pit cavity contained appreciable concentrations of intermetallic particles of copper aluminide (CuAl₂), nickel aluminide (NiAl₃), and copper-nickel aluminide (Cu₃NiAl₆), which suggested that they were the preferred sites for pitting. The resistance of the alloys to elevated temperatures and increased velocities is affected by SiC particles, reactivity of the metal surface due to intermetallic particles, and integrity of protective film.