Effect of the thickness reduction on intergranular corrosion in an under-aged Al-Mg-Si-Cu alloy during cold-rolling

The effect of the thickness reduction on the intergranular corrosion (IGC) of under-aged Al-Mg-Si-Cu alloy sheets during cold-rolling is investigated. The accelerated corrosion test shows that the IGC susceptibility increases firstly and then decreases gradually with increasing the thickness reductions of the cold-rolled sheets. Microstructural observations indicate that the increased IGC susceptibility results from the transformation of the initial low-angle grain boundaries to high-angle ones, whereas its decrease correlates with the small-sized grains formed at the high-angle grain boundaries. Furthermore, the difficulty for removing IGC by cold-rolling increases gradually in the sequence of short-transverse, longitudinal-short and longitudinal-transverse grain boundary planes.