Steam assisted oxide growth on aluminium alloys using oxidative chemistries: Part I Microstructural investigation.

The surface treatment of aluminium alloys under steam containing KMnO 4 and HNO 3 resulted in the formation of an oxide layer having a thickness of up to 825 nm. The use of KMnO 4 and HNO 3 in the steam resulted in incorporation of the respective chemical species into the oxide layer. Steam treatment with solution containing HNO 3 caused dissolution of Cu and Si from the intermetallic particles in the aluminium substrate. The growth rate of oxide layer was observed to be a function of MnO 4 − and NO 3 − ions present in the aqueous solution. The NO 3 − ions exhibit higher affinity towards the intermetallic particles resulting in poor coverage by the steam generated oxide layer compared to the coating formed using MnO 4 − ions. Further, increase in the concentration of NO 3 − ions in the solution retards precipitation of the steam generated aluminium hydroxide layer. [ABSTRACT FROM AUTHOR]