Correlating microstructure with the corrosion properties of Aluminum and Stainless Steel alloy

Abstract

The primary research objective was to develop a relationship between the microstructure and the material’s susceptibility to degradation in corrosive environments. Susceptibility to, and mechanisms of, corrosion were investigated using multiscale electron microscopy techniques. The specific material systems studied were Aluminum alloy 5456 and additively manufactured (AM) stainless steel 316L. Corrosion experiments combined with EBSD analysis were used to determine the microstructure influence on β phase precipitation and intergranular corrosion in Al5456 alloy. This combined approach facilitates the rapid characterization of a large number of grain boundaries (~28,000 in this study), providing a statistical framework for understanding the results produced in the earlier studies, which focused on relatively very small number of grain boundaries. The influence of extrinsic characteristics of grain boundary such as local dislocation density were investigated, and qualitative/quantitative observations were reported. Clear trends with GND were observed, with the fraction of uncorroded grain boundaries decreasing with the increase in GND density. For AM steel, the influence of native oxide film on the passive film characteristics and localized corrosion of SLM (selective laser melting) 316L stainless steel were studied. The analysis showed that corrosive attack varied between initial attack of Cr and Mo-enriched dislocation cell boundaries to cell interior depending on the presence of a native oxide film on the initial sample surface. A corrosion mechanism has been proposed to explain this variation in corrosion attack behavior. The Pitting behavior of these samples was evaluated, and the general corrosion performance was compared with the wrought counterparts.