| Regarding as the lightest metal structure material,magnesium alloys are widely applied in the field of digital electronics and aerospace.However,the poor corrosion resistance of magnesium alloy seriously limits its application.The most common way to improve the corrosion resistance of magnesium alloy is surface treatment,and the thermal control performance of the coating is required by the heat dissipation and insulation problems faced by electronic equipment and aerospace vehicles.The new green chemical conversion process,represented by phosphate chemical conversion coating,has attracted wide attention due to its low cost and simple process,while Plasma electrolytic oxidation process is favored for its excellent wear resistance and corrosion resistance.However,the previous research on chemical conversion coating mainly focused on corrosion resistance,and the research on its thermal control performance was few,and the research on improving its corrosion resistance and thermal control performance by micro arc oxidation using the coating forming liquid of phosphate conversion coating was very few.In view of the above problems,this paper has carried out the following research:1)Effect of different dispersants on the properties of phosphate chemical conversion coating.In this paper,seven dispersants were added into the coating forming solution of phosphate chemical conversion coating and nano SiC particles were dispersed on the surface of AZ91D magnesium alloy to prepare the conversion coating.The results showed that nano SiC particles were successfully introduced into the phosphate chemical conversion coating,and the corrosion resistance of the conversion coating with benzalkonium chloride and OP-10 as dispersants was significantly improved after the introduction of nano SiC particles.The emissivity and absorptivity of the seven conversion coatings were improved and reached the standard of high emissivity coating.2)Effect of different surfactants on the properties of phosphate chemical conversion coating.In this paper,seven kinds of surfactants were added to the solution of chemical conversion coating of phosphate to form the coating on the surface of AZ91D magnesium alloy.The corrosion test results showed that the corrosion resistance of the conversion coating with benzalkonium chloride and Tween 20 increased by more than 85%.The results of thermal control test showed that the emissivity of the conversion coating was more than 0.9 and the absorption rate did not change significantly.3)Study on the corrosion resistance and thermal control properties of conversion/plasma electrolytic oxidation composite coating.In this paper,a conversion/Plasma electrolytic oxidation composite coating was prepared on the surface of magnesium alloy by post-treatment of silicate plasma electrolytic oxidation coating with phosphate chemical conversion coating forming solution to improve the corrosion resistance thermal control performance of the coating,and the effect of SDS addition on the performance of the composite coating was studied.The results show that the corrosion resistance of the composite coating is improved after the phosphating solution treatment,while the long-term corrosion resistance of the composite coating is improved by the addition of SDS.The emissivity of the composite coating reaches the limit value of 0.99,but the absorption rate has no obvious change,so the coating with low absorption/emission ratio is obtained. |
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