Pioneering use of gel-electrolyte-based plasma electrolytic oxidation for improved ceramic coating on Al5052 alloy

Ceramic oxide coatings are critical for enhancing the corrosion resistance and durability of aluminum alloys used in aerospace, marine, and industrial applications. Plasma electrolytic oxidation (PEO) is widely used to form such coatings, typically in aqueous electrolytes. However, when conventional PEO is applied to large or complex-shaped components, its required high voltages and currents cause excessive electrolyte heating, boiling, and degradation. These conditions often result in porous, amorphous coatings with poor adhesion and protective properties. This study proposes the use of a gel-based electrolyte system for PEO, which has never been attempted; this gel electrolyte consists of an agar matrix containing sodium metasilicate or boric acid additives. This innovative approach enables localized surface treatment while minimizing thermal effects and ensuring coating uniformity. The resulting oxide-ceramic layers on Al5052 alloy samples had improved microstructures, higher crystallinity (up to 73.1 %), and better corrosion resistance, with polarization resistance reaching 702.8 kΩ cm², relative to a bare alloy. Notably, bond strength increased by more than four-fold compared with that of the bare alloy surface. These results highlight the potential of gel electrolytes as a viable, scalable alternative to the traditional electrolyte bath for PEO, offering new opportunities for fabricating high-performance, customizable ceramic coatings in advanced engineering applications.