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. ... Read more

Different thermomechanical processes have been used to modify the microstructure of elelctrolytic tough pitch copper (ETP-Cu) in terms of texture, mean grain and grain boundary length fraction. Electron backscatter diffraction (EBSD) and linear sweep voltammetry measurements were performed to study the relation between the macroscopic electrochemical behaviour and the microstructure. FE-SEM was used to visualise the surface after the potentiodynamic scans. The results indicate that there is only a small influence of the microstructure on the global electrochemical response of pure copper. The previously reported influence of the crystallographic orientation and grain boundary characteristics on the local corrosion behaviour of pure copper are not clearly reflected in the macroscopic electrochemical response. ... Read more