Structure and Property of Micro-arc Oxidation Coating Modified by Laser Melting and Solidifying on Aluminum Alloy

In order to improve performance and microstructure of micro-arc oxidation (MAO) coating, especially loose and porous characteristic, a laser melting and solidifying process (LSM) was introduced. Two kinds of samples were prepared: (1) MAO coatings, 18 mu m average thickness, were produced on 6082 aluminum alloy by bipolar current pulse in Na2SiO3-KOH solution. (2) a melting process using a Nd:YAG laser was employed to modify above-mentioned MAO coatings to obtain MAO+LSM coating. Microstructure of two kinds of coatings (MAO coating and MAO+LSM coating) were examined by scanning electron microscopy. X-ray diffraction was used to determine the phase composition of the coatings. Coating hardness was tested by ultra-micro hardness tester, and corrosion performance was investigated by polarization test instrument. The results show that the MAO+LSM coating is composed of dense layer, intermediate layer and melting layer from inside to surface. The loose layer of MAO film is replaced by a dense and low porosity melting layer after LSM treatment. The occupancy of alpha-Al2O3 phase in MAO+LSM is improved compared with MAO coating. Hardness and anticorrosion performance of MAO+LSM coating are also further strengthened while the remelted coating keeps the same binding manner as MAO coating.