Investigation of the role of strain and boehmite coating on the corrosion behavior of aluminum alloys.

The performance of aluminum alloys is affected by a combination of mechanical stresses and corrosive environments. The synergistic effect of mechanical deformation and a corrosive environment compromises the protective oxide layer of aluminum and thereby, accelerates degradation. While extensive research has been performed on stress-assisted cracking, research showing how aluminum alloys corrode with different surface conditions under applied strain remains largely unexplored. This investigation was designed to examine the corrosion behavior of aluminum alloys with and without boehmite coating under various applied strain values. Open circuit and potentiodynamic behavior of aluminum alloys were investigated by holding the material at a constant strain in a 3.5 wt% NaCl environment. A multimodal setup capable of simultaneously applying mechanical stress, carrying out electrochemical reactions, and imaging was designed for this study. Experiments were carried out at strain values below the yield point (0.05%), at the yield point (0.2%), and above the yield point (5%, 20%) to investigate polarization behavior, stress variation during polarization, and the roughness of corroded surfaces. The corrosion potential of the non-boehmited Al was observed to decrease by 30 mV with increasing applied strain. Additionally, the corrosion rate increased 15-fold from the unstrained sample to the 20% strained sample. These observations were attributed to the fracture of the oxide layer and the strain-dependent probability of metastable pit formation and stabilization. On the other hand, boehmite coatings on Al showed greater thickness and uniformity as compared to the native oxide layer. Consequently, the boehmite-coated samples exhibited a lower change in corrosion resistance during strain-assisted testing, underscoring the enhanced protective properties of the improved oxy-hydroxide layer under strain-assisted corrosive environments.