Improve The FSW Welds Performance Of The Aluminum By Micro-arc Oxidation

In the present study, the ceramic coating fabricated by micro-arc oxidation on aluminum alloys and FSW welds, studied the effect of Na2SiO3 concentration and technological parameters on the corrosion resistance of ceramic coatings, analyzed the formation mechanism of aluminum alloys and FSW welds. The electrolyte system was silicate system, and the additive was NaOH. The phase composition of the coatings were investigated by X-ray diffraction (XRD). The morphology of the coatings were investigated by Scanning Electron Microscopy (SEM) and Field Emission Scanning Electron Microscopy (FESEM). The porosity and the pore size were evaluated by Imagepro-plus. The Cross-section images of MAO coatings were evaluated by Metallurgical microscope, and the thickness of the coatings were measured by Imagepro-plus. The surface roughness of the coatings was characterized by Confocal Laser Scanning Microscope (CLSM). The corrosion properties of the ceramic coatings were evaluated by using a IVIUMSTAT automatic laboratory corrosion measurement system, and the results were analyzed by Zsimpwin. The change of technological parameters were as follows:Na2SiO3 concentration(10g/L,15g/L,20g/L), current density(7A/dm2,10A/dm2, 12A/dm2,15A/dm2), current frequency(300Hz,500Hz,700Hz,900Hz), oxidation time(20min,40min,60min). By virtue of detection and analysis, the results showed that, with the increase of Na2SiO3 concentration, content of γ-Al2O3 in the coatings, porosity and pore size of the coatings were decreased, thickness and surface roughness were increased at early and then decreased later, the corrosion resistance of ceramic coatings was enhanced. The best corrosion resistance of the coating was foamed at 15g/L. With the increase of current density, the content of γ-Al2O3 in the coatings was decreased, the porosity was increased at early and then decreased later, the thickness, pore size and the surface roughness were increased, the corrosion resistance of ceramic coatings were increased at early and then decreased later. As we all know, the bigger of the pore size, the easier of the corrosive media enter the coatings, The best corrosion resistance of the coating was foamed at 10A/dm2. The effect of current frequency was as follow:with the current frequency heightened from 300Hz to 900Hz, the content of γ-Al2O3 in the coatings, the pore size and surface roughness were decreased, while, the porosity was increased, the thickness was increased at early and then decreased later, the corrosion resistance was increased, the best corrosion resistance of the coating was foamed at 900Hz. The other electrical parameter, oxidation time, effected the coatings like this. Improved the oxidation time from 20min to 60min, the content of γ-Al2O3 in the coatings was decreased, the porosity was decreased, the pore size, surface roughness and thickness were increased, the corrosion resistance of ceramic coatings were decreased, the best corrosion resistance of the coatings was the one foamed at 20min. The thickness of dense layer and loose layer of aluminum alloy were both thinner than the welds, the striking voltage of FSW welds was lower than aluminum alloys(181V<260V). The film formation rate in the stage of spark discharge was lower, the shorter time of FSW welds stayed in the stage of anodic oxidation and the stage of spark discharge, the thicker of the coatings.