Yee Ng, Anna Marie Yong, Andrew Chun Yong Ngo, and Hongfei Liu
Abstract:
Alumina coatings were produced on Al6061-T6 substrates using a multi-step plasma electrolytic oxidation (PEO) process with the incorporation of Y2O3 nanoparticles (30~50 nm diameter) suspended in an aqueous electrolyte containing Na2SiO3 (10 g/L), NaOH (1.0 g/L), and glycerol (3.0 g/L). The resulting PEO coatings exhibit a typical bilayer structure consisting of a dense, crack-free inner layer and a porous outer layer with comparable thicknesses. By increasing the Y2O3 nanoparticle concentration in the electrolyte from 0 to 2.5, 5.0, 7.5, and 10 g/L, both elemental Y and crystalline Y2O3 contents in the coatings increased monotonically without causing significant changes in surface morphology or overall macrostructure. However, a gradual increase in coating thickness from ~30 to ~45 m was observed after a five-step process with a total treatment time of 60 min. This increase correlates well with the increase in average surface roughness (from 2.85 to 3.91 m) and dielectric breakdown voltage (from ~770 to ~880 V). Cross-sectional elemental analysis indicates that Y-containing inclusions are predominantly distributed in the outer layer rather than in the inner layer, following a depth-distribution trend similar to that of Si in the PEO coatings, although with different relative concentrations. Consequently, the microhardness of the dense inner layer (2094 ± 205 HV0.05), which is significantly higher than that of the Al6061 substrate (123.0 ± 4.6 HV0.05), remains essentially unaffected by the addition of Y2O3 nanoparticles to the electrolyte. Nanoindentation measurements further revealed that both the hardness and elastic modulus of the porous outer layer are lower than those of the inner layer, which may contribute to improved strain tolerance of the PEO coatings. The effects of Y2O3 nanoparticle incorporation on the mechanical and corrosion resistance properties of the PEO coatings will be discussed in detail.
License type:
Attribution 4.0 International (CC BY 4.0)
Funding Info:
There was no specific funding for the research done