Anisotropic Inter-granular Corrosion Behaviors and Microstructures of AlMgSiCu Alloy Sheets Made by Thermal–Mechanical Treatments

This study investigates the microstructure and local corrosion behavior of an Al–Mg–Si–Cu alloy, which has been subjected to cold-rolling with different deformation strain ratios (DSRs) and followed by artificial aging. Accelerated corrosion tests show that peak-aged samples with a small DSR (5–10%) are sensitive to inter-granular corrosion (IGC) along both the normal and rolling directions. When the DSR increases to medium strength (20–40%), IGC sensitivity decreases along both directions and corrosion propagates anisotropically. When the DSR is 60–80%, IGC sensitivity along the normal direction continues to decrease, but increases along the rolling direction, indicating pronounced corrosion anisotropy. Microstructural characterization reveals the decreased IGC sensitivity is mainly attributed to a reduction in element segregation at high-angle grain boundaries and the kinked and discontinuous grain boundary corrosion paths. The increased IGC sensitivity along the rolling direction could be related to the significantly flattened grains.