Consequences of Hot Rolling of Recycled AA5050 on Filiform Corrosion

The presence of a heavily deformed and corrosion susceptible surface/near-surface region on rolled aluminium alloy has been amongst the most important problems which the aluminium manufacturers are dealing with. While primarily the composition of the alloying elements and the thermo-mechanical treatment play an important role in determining surface activation, the importance of several other secondary parameters cannot be ignored. This paper tries to identify the impact of several factors, associated with sheet metal production, on the corrosion behaviour e.g. (a) type of the cast bar fed into the hot rolling mill, whether scalped or not scalped, (b) importance of homogenisation and in-line heat treatment, in relation to pre-existing understanding of surface activation on AA3005, (c) effect of hot and cold rolling (d) effect of surface finish, etc. The alloy under investigation was recycled AA5050, containing high Fe and Si as impurities, and used commercially for architectural purpose, eg. window facades.