Effects of Ce(NO3)3 concentration on microstructure and properties of plasma electrolytic oxidation layer on 6061 alloy

Abstract

Plasma electrolytic oxidation treatment of 6061 Al alloy was carried out in a sodium silicate and sodium hydroxide alkaline electrolyte containing different concentrations of cerium nitrate (Ce (NO3)3) under constant current mode. The effects of Ce (NO3)3 concentration on the roughness, cross section and surface morphology, composition and phase composition, adhesion force and corrosion resistance of the prepared layer were studied by means of true color microscope, scanning electron microscope, x-ray energy spectrometer, x-ray diffractometer, micrometer scratcher and electrochemical workstation. The results show that with the increase of Ce(NO3)3 concentration in the electrolyte, the thickness of the plasma electrolytic oxidation layer increases gradually, and the micropores and cracks increase, and the roughness increases first and then decreases. The plasma electrolytic oxidation layers under different concentrations of Ce (NO3)3 are mainly composed of α-Al2O3, γ-Al2O3 and a small amount of Al2SiO5. The Ce element in the layer is mainly present in the form of a mixture of Ce(OH)4, CeO2 and Ce2O3.The increase of Ce (NO3)3 concentration reduces the binding strength between the plasma electrolytic oxidation layer and the matrix, increases the self-corrosion potential, decreases the self-corrosion current, and weakens the corrosion resistance. The layer with a concentration of 0.25 g l−1 Ce (NO3)3 has less micropores and cracks, and has the better compactness. The bonding strength between the layer and the substrate is 27 N, the corrosion current density is 3.42 × 10−9A cm−2 and corrosion potential is −0.72 V, the best bonding strength and corrosion resistance is presented.