Fabrication of ultra-thick SiO2/Al2O3 composite coatings by PEO in organosilicon electrolyte and study of thermal control and corrosion resistance properties

Achieved coatings exhibiting coexistence of crystalline and amorphous SiO 2 phases. • Revealed the three-dimensional distribution and phase composition of coating pores. • Elucidated the mechanism by which SiO 2 coatings influence thermal management performance. • I corr is reduced by more than two orders of magnitude compared to the matrix. This study addresses the insufficient thermal stability and corrosion resistance of 7075 aluminium alloy by employing staged voltage-boosted plasma electrolytic oxidation (PEO) technology to fabricate an ultra-thick composite coating containing amorphous/crystalline SiO 2 within an organosilicon electrolyte. The system investigated the regulation mechanisms of duty cycle on coating phase composition, microstructure, thermal control performance, and corrosion resistance. Utilising advanced characterisation techniques such as Grazing Incidence X-Ray diffraction, X-ray computed tomography, and X-ray photoelectron spectroscopy, its underlying mechanisms were elucidated. By modulating energy input, the duty cycle significantly influenced coating growth, achieving a maximum thickness of 181.76 μm-far exceeding conventional PEO coating thickness levels. XCT analysis revealed the phase distribution and pore characteristics of the coating at a 20% duty cycle. Pores with diameters between 0 and 5 μm constituted the highest proportion (approximately 68.85%), while interconnected pores exceeding 30 μm in diameter dominated the total pore volume. Optimal thermal management performance was observed at a 30% duty cycle (absorptance 0.36, emissivity 0.89), confirming a critical thickness threshold (130 μm) and the pivotal role of amorphous SiO 2 . Corrosion resistance peaked at a 10% duty cycle, with corrosion current density reduced to 2.368 × 10 −8 A·cm −2 , representing a near two-order-of-magnitude decrease compared to the substrate. Download: Download high-res image (349KB) Download: Download full-size image