| Magnesium alloy has been widely used because of its light weight andexcellent performance, however, the poor corrosion resistance of magnesiumalloy limits the industrial application due to its high activities. Researchesemphasized on improving the corrosion resistance of magnesium alloy usingvariety surface treatment technology. Micro-arc oxidation technology wasrecognized as one of the most promising magnesium alloy surface treatmenttechnology. It can form ceramic layers well combined with high hardness,excellent wear resistance and corrosion resistance. However, the ceramic layerformed on the surface shows a porous structure because of the high breakdownvoltage formed in micro-arc oxidation process. In this paper, an in-situ sealingtechnique by using nano-Al2O3oxide colloids into the MAO electrolyte wasapplied to solve this problem. The effect mechanism of additive on the corrosionresistance was analyzed. For further coordination deformation properties of theceramic layer and of magnesium alloy matrix, a technique by combining ofmagnetron sputtering and MAO was used to produce MAO/Al multilayercoatings on magnesium alloy. The microstructure and corrosion resistance of multilayer coatings were discussed, which will provide theoretical basis andtechnical reference for the application of the magnesium alloy in complexconditions. The main results were shown as follows:(1) Ceramic layers which formed by in situ adding of Al2O3colloid forsealing treatment were mainly composed of MgO, Mg2SiO4, MgSiO3, Al2O3andMgAl2O4phases. The element of Al in the layers was in the form of Al2O3andMgAl2O4.(2) The thickness of ceramic layers increased and the number of holes andsize of holes deduced by adding Al2O3colloid in the electrolyte.(3) Ceramic layers by in situ adding Al2O3colloid showed better corrosionresistance and wear resistance than that without Al2O3colloid, the layer withadding Al2O3colloid at late period of total oxidation time6min (about the totaloxidation time of3/5) performed the best property.(4) The corrosion rate was reduced evidently with the increase of Al2O3colloid dosage, however, the performance of corrosion resistance was hardlyinfluenced when the colloid was exceeded.(5) The MAO/Al multilayer coatings were composed of MAO ceramic layer,pure Al layer and interlayer diffusion layer. The layer with in situ sealing byAl2O3colloid showed thicker thickness, more continuous surface topographyand better corrosion resistance than the one without Al2O3colloid sealing. |
PDF Full Text Request