Growth behavior of energy-efficient protective black flash-PEO coatings on additively manufactured aluminum‒silicon alloys

Abstract

The energy-efficient flash-PEO (plasma electrolytic oxidation) approach is being investigated to develop thin black protective PEO coatings on Al10SiMg alloys fabricated through SLM (selective laser melting). The effects of various Flash-PEO treatment durations, ranging within 2–5 min, were investigated in an electrolyte composed of phosphate, Na-EDTA, and sodium hydroxide, with ammonium metavanadate added as a coloring additive. The correlation among the coating composition, black coloration, and corrosion resistance performance was examined via structural analysis, energy consumption during the process, and EIS analysis. The findings indicate that treatment duration, up to the limit of 4 min, substantially influences the development of VOx compounds that demonstrate the black hue, with the color transition occurring between 2 and 4 min. However, extending the treatment time beyond this limit yielded no further enhancements in color intensity or corrosion resistance. Furthermore, the coating demonstrated an energy consumption of 1–2 kW h m−2·μm−1, increasing the system's hardness by up to five orders of magnitude relative to the bare substrate, yielding |Z|10mHz 3 × 104 Ω cm2 after 10 days of immersion in 3.5 wt% NaCl solution, while retaining up to 90 % of its ΔE (blackness).