Investigation of mechanical properties of corrosion products in AA7075-T651 using in situ nanoindentation

Aluminum alloys benefit from the formation of a passivating layer for protection against atmospheric corrosion. However, mechanical damage to this layer can expose the underlying material, initiating localized corrosion and compromising structural integrity. Despite its critical role, the evolution of the mechanical properties of the corrosion product layer under dynamic environmental conditions remains poorly understood. This study investigates the microstructural and micromechanical behavior of the corrosion product layer formed in an AA7075-T651 alloy in an aqueous chloride solution. In situ nanoindentation experiments were performed to measure mechanical properties, while chemical composition and phase evolution were analyzed using electron microscopy and Raman spectroscopy. The results reveal that prolonged immersion leads to a reduction in the Young’s modulus and hardness of the corrosion layer attributed to chloride ion infiltration in the oxide layer inducing microporosity. Furthermore, transitioning the corrosion layer from an aqueous to a dry atmospheric environment induces microcracking due to dehydration and the loss of crystallinity in the AlOOH phase. This transition may also involve a phase transformation from AlOOH to Al(OH)₃, attributed to structural changes within the corrosion products, reducing their mechanical integrity. These findings provide critical insights into the degradation mechanisms of aluminum alloys corrosion layer in chloride-rich environments, supporting the development of advanced materials and coatings with enhanced mechanical and corrosion resistance.