Studies on Potentiodynamic Polarization Behaviour of Cryorolled Al-Mg-Si Alloy

Cryorolling is considered to be the prominent processing method to develop high strength light weight alloys. Even though considerable work is available on mechanical properties of cryorolled materials, no detailed studies are available on corrosion behavior of these cryorolled sheets. Al-Mg-Si alloy is cryorolled to 50% and 75% reduction at -196 degrees C and also at room temperature. Potentiodynamic polarization studies were performed on these rolled sheets in 3.5 wt% NaCl solution and the results were compared with those of the annealed and solutionized samples of Al-Mg-Si alloy. Irrespective of the rolling temperature, all the rolled samples, except for LNR 75%, exhibited inferior corrosion resistance compared with those of the reference samples. This is attributed to the large amount of internal stresses and sub-grain network developed during rolling. The rolled samples evidenced peak shift compared to those of the annealed and solutionized samples and higher peak broadening is observed, which is due to the development of higher grain boundary area and enhanced lattice strains along with large dislocation densities. These grain boundaries and dislocation densities are the root cause for the inferior corrosion properties of the rolled samples.