Microstructure‐dependent corrosion of herringbone‐grooved embossed Al–1.1 wt% Mn strips for heat exchanger tubes

This paper studied the effect of embossing on the microstructure and corrosion behaviour of an Al−1.1 wt% Mn sheet. The microstructure of the embossed Al−1.1 wt% Mn sheets was studied by differential interference contrast microscopy, scanning electron microscopy, transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, focused ion beam microscopy and X‐ray computational tomography. Finite element modelling was used to assess the stress and strain distribution developed during embossing, and to support the experimental analyses. The corrosion behaviour of the embossed sheets was assessed using potentiodynamic anodic polarisation tests, followed by corrosion surface morphology analysis. Results showed a microstructural evolution of the alloy during embossing, which is dependent on both the embossed pattern geometry and the roll forming direction. Nonsymmetrical displacement of material, in respect to the pattern geometry, was caused by the anisotropic forming pressure applied on the strip during roll forming, which yielded the formation of more susceptible sites for pitting and intergranular corrosion on the embossed aluminium surfaces.