The degradation of ultra-fine grained aluminum alloys involves multiple localized corrosion mechanisms at once which make its understanding complex. Here we investigate the electrochemical response of a partially recrystallized ultra-fine grained AA6061 alloy after a low-temperature post-aging treatment. Our results show that the anodic current density, the severity of the filiform corrosion along the shear direction, and the intergranular corrosion are significantly influenced by the precipitation within the shear bands, being the highest at peak aging. Also, passivation is enhanced but the passive film is less stable after ECAP regardless of the low- temperature post-aging treatment. because of the high density of dislocation, precipitates, and grain boundary in the extruded material.

The formation of shear bands during high strain deformation processes is known to promote grain refinement and better mechanical response. However, the literature on how shear bands affect corrosion of aluminum alloys, supported by relevant microstructure characterizations is scarce. Here we provide insight into precipitate aggregation phenomena in a partially recrystallized microstructure. We elucidate how shear bands affect the material's corrosion susceptibility and degradation mechanism. Our results demonstrate that shear bands, in ultra-fine grained aluminum alloys, are preferential sites for pitting and intergranular corrosion due to particle segregation.

The low intergranular corrosion resistance of extruded aluminum alloys is a limiting criteria for several applications. In this work, we investigated the effects of shear deformation, dynamic recrystallization and peak aging on the corrosion susceptibility of an AA6061 alloy up to seven ECAP passes following route Bc. We assessed intergranular corrosion susceptibility using the standard ISO test 11846 (Method B). Our results show that dynamic recrystallization improves the localized corrosion resistance of severely deformed AA6061 by reducing the fraction of shear bands in the material. We found a clear difference in surface reactivity between the recrystallized grains inside and outside the shear bands, suggesting that in this material grain-stored energy influences corrosion more than grain boundary precipitation. In parallel, we characterized the degradation of conventionally extruded AA6061-T6. The results reveal that shear deformation is a promising process for extruded aluminum alloys with improved strength and intergranular corrosion resistance.

It is important to find environmentally friendly replacements for chromate conversion coatings (CCCs) that are effective anticorrosion layers. In this work, high corrosion resistance is demonstrated with ultrathin (and transparent) multilayer coatings deposited on an aluminum alloy. Cationic polyurethane (PU) and anionic vermiculite clay (VMT) multilayer films were deposited from aqueous solutions using layer-by-layer assembly. The combination of relatively hydrophobic polyurethane and highly aligned clay platelets leads to excellent barrier properties for the PU/VMT coating in an aqueous environment. A 30 bilayer PU/VMT coating, with a thickness of only 300 nm, provides 2 orders of magnitude improvement in impedance and imparts corrosion protection for 5 days. Another advantage of this unique coating system is that no surface treatments are required prior to coating due to the strong adhesion of polyelectrolytes to the metal. The work demonstrates the use of novel LbL assembled nanocoatings as a potential replacement for chromate conversion pretreatments.