Role of anodic precursor layer thickness on PEO coatings: energy consumption and long-term corrosion performance

Abstract

PEO coatings with different thickness of anodic precursor films (5, 10, 20 and 40 μm) were successfully developed on AA2024 with the aim of determining how the thickness of anodic films affects the development of PEO film, structural growth, surface morphology, phase composition, and associated long term corrosion resistance properties. Compared to direct PEO treatment, reductions in the energy consumption (kW.h.m2.μm−1) of 71 %, 41 %, and 17 % are obtained at similar PEO processing conditions for the pre-anodized specimens of 40 μm, 20 μm, and 10 μm film thickness, respectively, while the time to current drop for above specimens reduced to 86.2 %, 63.3 % and 33.3 %, associated to the early formation of the “soft sparking” regime. The results suggest the effectiveness of pre-anodization on the PEO coatings for minimum energy consumption, developed explicitly on 20 and 40 μm anodic film, whereas overall PEO on anodic precursors exhibited a thicker oxide layer, homogenous pore size distribution, and long-term corrosion protection comparable to the original PEO layer. Based on the energy consumption and corrosion resistance of PEO on anodic precursor, a model of PEO coating growth is proposed, which can be considered a thorough insight towards highly developing energy-efficient PEO for practical applications.