MAO coatings with high breakdown voltage fabricated by multilayer strategy

With power electronic devices advancing toward higher voltages, there is a growing demand for insulating coatings with high dielectric breakdown strength. Micro-arc oxidation (MAO) can form ceramic coatings on aluminum alloys, but its porous structure limits performance. Here, an alternating aluminum (Al) deposition/MAO multilayer strategy is proposed to achieve cumulative enhancement. Namely, a dense Al layer is deposited via continuous high-power magnetron sputtering (C-HPMS) to seal pores and regulate subsequent MAO discharge, enabling stable repeated oxidation. The influence of Al interlayer thickness on surface morphology, discharge behavior, and breakdown strength was studied. Thin Al layers cannot effectively seal the pores, causing local field distortion and unstable arc discharge, resulting in limited improvement. When the Al layer reaches a critical thickness of ∼35 μm, pore bridging and surface planarization are achieved, forming an equipotential interface that suppresses field concentration. This enables uniform micro-spark discharge and produces coatings comparable to the initial MAO layer. The breakdown voltage reaches 998 ± 23 V (∼17.21 kV/mm) for a bilayer and 1400 ± 100 V (∼16.09 kV/mm) for a trilayer. This strategy offers an effective route to overcome the breakdown limitation of MAO coatings and develop reliable insulating ceramics.