The behaviour of iron-containing intermetallic particles in aluminium alloys in alkaline solution

The behaviour of Fe-containing particles during alkaline etching and desmutting of AA5052 aluminium alloy is investigated by quasi in situ monitoring of the compositional and morphological evolution of the particles. In alkaline solution, multi-layered oxide/hydroxide films are rapidly formed on the particles, rendering them electrochemically inactive. The particles are inactive in nitric acid due to formation of thin alumina layer. The treatment doesn't significantly change the total population of Fe-containing particles with the population of Al3Fe being reduced and that of Al(Fe,Mn,Cr)Si remaining almost unchanged. Further, relevance of the observed behaviour to localized corrosion of aluminium alloys is also discussed.