The occurrence of preferential grain etching (PGE) during alkaline etching of aluminum extrusion alloys from the 6XXX series is often linked to the presence of certain impurity elements such as zinc, causing an undesired etching appearance. In the presented work, an additional culprit in this context is identified, which has not been investigated yet. A clear relation between PGE and the presence of a subsurface shear layer is identified for extruded Al 6060 alloys containing 0.02 and 0.06 wt% Zn. This shear layer can be distinguished from the bulk of the metal by its difference in crystallographic texture as visualized by electron backscatter diffraction (EBSD). For the Zn enriched alloy, the <111>//ND grains are etched away faster than grains with other orientations, resulting in the grainy appearance typical for PGE. Independent of the Zn content in the alloy, once the shear layer is removed and <111>//ND grains are practically absent on the new surface, the depths variations caused by preferential etching disappear. Instead, the surface of the alloy is attacked uniformly by the caustic etch bath.

Lithium salts were investigated as leachable corrosion inhibitor and potential replacement for hexavalent chromium in organic coatings. Coatings loaded with lithium carbonate or lithium oxalate demonstrated active corrosion inhibition by the formation of a protective layer in a damaged area. The present paper provides more insight into the formation and composition of the protective layer in a damaged area generated from the lithium salt loaded coatings when exposed to neutral salt spray testing conditions (ASTM B-117). Lithium-ion leaching from the coating matrix was demonstrated with atomic absorption spectroscopy and the pH conditions in the damaged area were determined with a scanning ion-selective electrode technique. Additionally, the formation of the protective layer was studied with microscopic and surface analytical techniques. Scanning electron micrographs and Auger electron spectroscopy depth profiles revealed the process of coverage and growth of the protective layer in the damaged area. Furthermore, X-ray photoelectron spectroscopy analysis indicated that the protective layer likely consists of a hydrated oxide in the form of a (pseudo) boehmite with lithium distributed in its matrix.