Microstructural and Mechanical Properties of a Hard Anodic Coating Applied on an Elastically Prestrained Aluminum Substrate

Abstract

Hard anodization is an electrochemical procedure used on aluminum and its alloys to enhance tribo-corrosion performance by creating a thick oxide layer. Thermal residual stresses, resulting from the difference in the coating and substrate's thermal expansion coefficient, promote crack initiation and reduce the high-cycle fatigue strength (HCF). This work hypothesizes that elastically prestraining the aluminum substrate can compensate for this mismatch, minimizing coating irregularities and improving fatigue strength without developing a new anodizing strategy for fatigue-sensitive anodized components. Aluminum alloy 6082 is used as the substrate, and a device is built to apply tensile forces of 800 and 1000 N. Subsequently, the prestrained specimens are hard-anodized with timeframes of 15 and 30 min, and the coating thickness, hardness, and morphology are determined. In addition, the HCF of the coated sample is analyzed and compared with the uncoated sample. Results reveal that prestraining influences the coating formation and characteristics, causing early crack initiation and fatigue failure. The observations show that tensile prestrain exacerbates coating deterioration rather than mitigating it, showing the complex interaction between the prestrain and thermal stresses in coating processes. This study demonstrates that prestraining combined with anodizing degrades the HCF performance of coated aluminum alloy.