Corrosion presents an inherent challenge in the safe and effective use of metallic aerospace structures for extended periods of time. Progress in the fundamental understanding of corrosion initiation and propagation under stress requires a multi-scale approach that leverages experiments to develop predictive models. Although there exists a large amount of research results tracking the corrosive processes of anodic dissolution and hydrogen embrittlement, the amount of available data and modeling of the micro-scale initiation of corrosion is sparse. This work leverages a suite of characterization techniques to systematically analyze an aerospace grade aluminum alloy AA7075-T6, providing important multi-scale data for correlation with overall corrosion progression. Samples were exposed to 3.5% NaCl solution at various exposure times under loading with a micro-tensile system. Optical microscopy, Raman spectroscopy and Energy Dispersive X-ray Analysis provided spatial maps of the visual and chemical alloy signatures before, during, and after failure, to analyze and track the progression of corrosion. An experimental setup for in-situ Digital Image Correlation (DIC) was developed to provide strain maps to study local concentrations around corrosion pits and quantify the impact on the material tensile performance. The material morphology and composition from these measurements identified localized oxide formations at a high spatial resolution that can be used to quantify the corrosion rates. Meanwhile, in-situ DIC measurements provided results showing stress concentrations formed by the corrosion pits and the reduced mechanical performance with exposure. The results demonstrate that multiple factors affect corrosion susceptibility and material deterioration, and highlight the need to overcome experimental challenges in quantifying these factors distinctly. This work demonstrates the capacity for highly detailed analysis of corrosion initiation and propagation in affected alloys using the processes outlined in the systematic study. The outcomes provide a pathway to address methods for maintaining the integrity of these alloys and extending their lifespan.
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Master of Science in Aerospace Engineering (M.S.A.E.)
College of Engineering and Computer Science
Mechanical and Aerospace Engineering
Aerospace Engineering; Space System Design and Engineering
Length of Campus-only Access
Masters Thesis (Open Access)
Reed, Nicholas, "Development of Multi-Scale Characterization Techniques for Stress Corrosion Cracking of Aerospace Alloys" (2021). Electronic Theses and Dissertations, 2020-. 746.