A Difference-Imaging Technique Used to Study Streaking Corrosion of Aluminum Alloys AA7075 and AA8006 in Chloride Solution

Abstract

We observed corrosion forming streaks in chloride solutions along abrasion grooves, or grooves formed during rolling, using an in situ difference-imaging technique. Streaking occurred on an abraded zinc-containing alloy AA7075-T6, and also on as-received or abraded and heat-treated alloy AA8006, which is representative of alloys known to suffer filiform corrosion. In both alloys, streaking was due to a susceptible surface layer. This similarity contrasted with marked differences in how susceptibility developed, i.e., by abrasion in Al–Zn, and thermomechanical treatments in alloys prone to filiform corrosion. Mechanisms are discussed for streaking based on pH changes around growing streaks.