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Hydraulic steel structures (HSS) are key components of U.S. Army Corps of Engineers infrastructure and are subject to corrosive environments, unpredictable loadings, and extreme conditions. Corrosion can take many forms and can cause costly damage to HSS due to inadequate design of protective measures. There are numerous forms of corrosion that have a negative effect on HSS, as well as material properties that need consideration when design HSS preventive measures. Understanding corrosion and providing proper preventive measures is crucial for HSS. Proper maintenance and repair of these protection systems also play a significant part in corrosion control of HSS.

In this study, a new consistent formulation coupling kinematics, thermodynamics, and kinetics with damage using an extended multiplicative decomposition of the deformation gradient that accounts for corrosion effects is presented. The technical approach used for modeling the corrosion behavior of magnesium alloys was divided into three primary steps. First, a predictive corrosion model was developed based on experimental corrosion observations. The experimentally-observed corrosion mechanisms of pitting, intergranular, and general corrosion on the AZ31 magnesium alloy were quantified in 3.5 wt.% NaCl immersion and salt spray environments using optical microscopy and laser profilometry to document the changes in the pit characteristics. Although both environments showed similar trends, the immersion environment was more deleterious with respect to intergranular and general corrosion. On the other hand, the salt-spray environment allowed deeper pits to form throughout the entirety of the experiments, which led to a substantial thickness drop (general corrosion) compared with the immersion environment. Next, the complete corrosion model based upon the internal state variable theory was formulated to capture the effects of pit nucleation, pit growth, pit coalescence, and general corrosion. Different rate equations were given for each mechanism. Following the formulation of the model, the aforementioned experimental work and experimental work on four other magnesium alloys (AZ61, AM30, AM60, and AE44), was used to validate the model.

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