Localized corrosion of an ultrafine grained Al–4Zn–2Mg alloy produced by cryorolling

The effect of microstructure on corrosion behaviour of an ultrafine grained (UFG) Al–4Zn–2Mg alloy produced by cryorolling was investigated. Both UFG and coarse grained (CG) alloys in peak-aged condition were subjected to potentiodynamic polarization and intergranular corrosion (IGC) tests in chloride solutions. UFG alloy exhibited increased corrosion potential (Ecorr), decreased corrosion current density (icorr) (−864 mVSCE, 0.60 μA/cm2) during polarization and lower weight loss during IGC when compared with CG alloy (−902 mVSCE, 4.9 μA/cm2). Improved corrosion resistance of UFG alloy is mainly attributed to sub-micrometer grains, absence of coarse MgZn2 anodic precipitates and precipitate-free zones along the grain boundaries.

► Cryorolling of Al–4Zn–2Mg alloy produced UFG structure with modified precipitation.
► Corrosion behaviour is determined using both electrochemical and immersion tests.
► UFG alloy exhibited improved corrosion resistance than the coarse grained alloy.
► Corrosion behaviour is correlated with microstructure of UFG Al–Zn–Mg alloy.
► Improvement is due to absence of coarse precipitates and precipitate-free zones.