Effect of pH Change on the Electrochemical Behavior of Intermetallic Particles in AA1050 Aluminum

Abstract

Commercial purity aluminum alloys, such as AA1050 and AA1100, are widely used for infrastructure and battery materials for their high formability, high electrical conductivity, and excellent corrosion resistance. The commercial purity aluminum alloys are known to contain Fe-rich intermetallic particles (IMPs). Although the IMPs are needed to provide the valuable properties, some of the IMPs could turn into an initiation site for pitting under salty environments. Since the Fe-rich IMPs show higher electrode potential than that of the Al-matrix, the IMPs work as a cathodic reaction site. As oxygen reduction reaction proceeds on the IMPs, the pH around the IMPs increases locally. The dissolution of the Al-matrix (often referred as trenching) is caused by the local alkalization, and a trench is formed around the IMPs. Crystallographic pitting is likely to be initiated inside the trench. Although the IMPs have an important role in trenching, the electrochemical behavior of the IMPs during trenching is still unknown. In this study, the dissolution behavior of the IMPs and surrounding Al-matrix was observed in situ using an optical microscopy in order to analyze the morphological change during trenching. The effect of pH change on the electrochemical behavior of the IMPs was analyzed using the bulk IMPs fabricated by arc-melting.