Passive Film Structure and Corrosion Initiation in Al Alloys with Far-from-Equilibrium Compositions and Microstructures

Al alloys with far-from-equilibrium compositions and microstructures are reported to possess high corrosion resistance and strength. These alloys produced are by non-equilibrium processing techniques such as high-energy ball milling, sputtering, and ion implantation. Depending on the processing techniques and conditions, the microstructure of the alloys could be heterogeneous. For example, alloys produced by high-energy ball milling and subsequent consolidation comprise a matrix with high solid solubility of the solute and uniformly distributed secondary phases. Such a heterogeneous microstructure is expected to influence the passive film composition and localized corrosion mechanisms. In the present study, passive film composition on the ball-milled alloys was studied using a combination of scanning transmission electron microscope, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry (SIMS). Additionally, pits and regions near pits were investigated which helped in understanding factors causing pit initiation and repassivation.