The Effect of Deformation Mode and Microstructure on the IGC Susceptibility of Al–Mg–Si–Cu Alloys for Automotive Applications

Intergranular corrosion (IGC) can occur in 6000 series alloys due to the formation of corrosion-active Mg2Si phases or copper-enriched nanofilms at the grain boundaries. The formation of these films highly depends on the alloy composition and thermomechanical history such as the deformation degree and the grain morphology. The present study explores the underlying mechanisms of IGC of different industrially-used extruded, rolled, and cast 6000 series aluminum alloys with high copper contents using standardized immersion tests (DIN EN ISO 11846 B). A particular focus is set on the influence of processing parameters on the grain size and morphology and their effect on the corrosion susceptibility. The results are correlated to the microstructure using optical light microscopy, Barker etchings and scanning electron microscopy. The corrosion susceptibility as well as the corrosion mechanism was found to be highly dependent on the processing route, the resulting grain structure and the dislocation accumulation through deformation.