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 (E-corr), decreased corrosion current density (i(corr)) (-864 mV(SCE), 0.60 mu A/cm(2)) during polarization and lower weight loss during IGC when compared with CG alloy (-902 mV(SCE), 4.9 mu A/cm(2)). 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. (c) 2012 Elsevier Ltd. All rights reserved.