Localized Corrosion and Passive Film Characteristics of Additive Vs. Wrought Al-Zn-Mg-Cu-Based Alloy

Abstract

Al-Zn-Mg-Cu alloys of the 7xxx series have proven to be excellent candidates for the aerospace, defense, and automotive industries due to their high strength to weight ratio, high corrosion resistance, and fatigue performance. For additively manufactured alloys manufactured using laser powder bed fusion (LPBF), the non-conventional microstructures formed as a result of one or more factors like alloy modification, LPBF process, and subsequent thermal treatments can lead to change in corrosion behavior and mechanisms.Using scanning vibrating electrode technique (SVET) and immersion tests in chloride environments, this work concentrates on understanding the localized corrosion behavior of additively manufactured Al-Zn-Mg-Cu based alloy in comparison with its wrought counterpart. To understand the corrosion mechanisms, microstructures including the precipitates are characterized at different length scales using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and correlated with the corrosion behavior. The difference in passive film characteristics of additive vs. wrought Al-Zn-Mg-Cu based alloy is studied using electrochemical impedance spectroscopy (EIS) and X-Ray photoelectron spectroscopy (XPS) characterization. Overall, the LPBF-based alloy studied shows better corrosion performance than the wrought counterpart in chloride environments. The microstructural differences and mechanisms responsible for this behavior is proposed.