Corrosion properties of submerged friction stir modified as-cast nickel-aluminum bronze (NAB) compositions

Abstract

This study aimed to analyze the effects of adding alloying elements and cooling medium during friction stirring on the electrochemical and immersion corrosion properties. The results showed that the addition of nickel and iron prevented the formation of an unfavorable phase γ2 and instead produced intermetallic compounds κ in the microstructure. Friction stir processing (FSP) helped refine and homogenize the coarse and inhomogeneous structure of the casting, and also eliminated casting defects, whether performed in air or underwater conditions. The polarization and electrochemical impedance tests revealed that, in most cases, FSP led to a decrease in electrochemical and short-term corrosion behaviors as compared to the as-cast specimens, under the impact of alloy composition and active cooling. However, the weight loss immersion tests indicated that the friction stir processed alloys, particularly those processed underwater, demonstrated the best long-term corrosion properties. It was observed that the corrosion product film created on all models after immersion had a similar composition.