Effect of cryogenic cooling on corrosion of friction stir welded AA7010-T7651

Purpose - The purpose of this paper is to study how cryogenic CO2 cooling during the welding process affects corrosion behaviour of friction stir welding (FSW) AA7010-T7651. Design/methodology/approach - Friction stir welded AA7010-17651 was produced with a rotation speed of 288 rpm and a travel speed of 58 mm/min. The liquid CO2 was sprayed onto the weld centre line immediately after the toolpiece. The microstructures of welds in different regions were observed using Field Emission Gun Scanning Electron Microscope (FEG-SEM). The effect on the corrosion susceptibility was investigated using a gel visualisation test and potentiodynamic polarisation measurements using a micro-electrochemical technique. Findings - The main corrosion region for both FSWs AA7010-T7651 produced with and without cryogenic CO2 cooling is in the HAZ region, which exhibited intergranular attack. Cryogenic cooling does not show any influence on anodic reactivity of the weld region (both nugget and HAZ) compared to uncooled weld metal. However, the width of the reactive HAZ is reduced after cooling, as compared to the uncooled weld. The cooled welds show higher cathodic reactivity in the nugget region than does the nugget region of uncooled welds. Originality/value - There has been no previous work to investigate the effect of cryogenic CO2 cooling on the corrosion behaviour of FSW AA7010-T7651. The paper relates the microstructures of both uncooled and cooled welds to their anodic and cathodic reactivities using a micro-electrochemical technique.