The effects of current density on the phase composition and microstructure properties of micro-arc oxidation coating

摘要

Ceramic coatings have been synthesized on the Al alloy substrate by micro-arc oxidation (MAO) technique. The effects of current density on the mechanical and chemical properties of MAO coatings have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), and micro-hardness test. The samples fabricated at high current density consist mainly of alpha-Al_2O_3, while the samples fabricated at low current density are almost composed of gamma-Al_2O_3. XRD analysis at different depths from coating surface towards substrate indicates that there is a complicated variation of alpha-Al_2O_3 content as a function of depth, which is different from the results of others. Micro-hardness test shows that these kinds of samples have high hardness. However, in the plane parallel to the substrate, there is a non-uniform distribution of hardness for the samples deposited at high current density, which can be attributed to the non-uniform distribution of pores in the same plane parallel to the substrate.