Effects of negative voltage on microstructure, electrical insulating, anti-corrosion, and thermal physical performance of plasma electrolytic oxidation coating on SiCp/Al composite

Abstract

PEO coating microstructure on SiCp/Al composites under the influence of negative pulse are comparatively studied. Results show that the cross-sectional porosity is significantly reduced to 5.1%. The electrical insulation performance of coatings initially improves and then declines as the negative voltage rises from 0 V to 120 V, which is attributed that either an excessively low or excessively high negative voltage is insufficient to improve the internal defects of the coating. Among all the coatings, the coating obtained at +500 V/−80 V (i.e., N80) possesses better electrical insulation (with breakdown voltage of 736 ± 15 V, dielectric strength of 16.3 ± 0.3 V/μm, electrical resistivity of 1.51 × 1011 Ω∙cm), better dielectric performance, higher optical band gap value, making it appropriate for usage as electronic packaging or dielectric materials. The impedance modulus at low frequency of N80 coating is two to three times higher than that of N0, N40, and N120 coating, providing a long-term anti-corrosion ability for the substrate, during the 72-hour immersion. Additionally, the coatings display a high infrared emissivity in the waveband of 8–20 μm (>0.9) to achieve good radiation and heat dissipation effect. Thus, a reasonable negative voltage used in coating preparation does effectively diminish internal structural defects, enhancing coating performance.