AZ31B镁合金表面等离子喷涂陶瓷层的微观结构及耐蚀性

Microstructure and CorrosionProperty of Plasma Sprayed Ceramic Coating on AZ31B Magnesium Alloy

采用等离子喷涂方法在AZ31B镁合金表面制备Al_2O_3、Al_2O_3-13%TiO2(AT13)和Al_2O_3-20%TiO_2(AT20)三种陶瓷涂层;对比研究陶瓷层的微观组织结构、孔隙率、结合强度及电化学腐蚀性能。结果表明:等离子喷涂的陶瓷涂层具有典型的层状结构,涂层具有良好的结合强度和较低的孔隙率。随着TiO2加入量的增多,陶瓷涂层的结合强度升高,孔隙率降低,耐蚀性提高;AT20涂层与镁合金基体相比自腐蚀电位升高了701mV,自腐蚀电流密度降低了两个数量级,阻抗是基体的6倍,AT20涂层的耐蚀性最优。陶瓷涂层的电化学腐蚀过程表现为膜层局部腐蚀和基体腐蚀并造成涂层层状剥离。

Magnesium alloys are widely used in areas such as aerospace, transportation, 3C products, printing and textiles, and have become preferred for lightweight structural materials in aerospace and industrial applications. However, the poor corrosion resistance seriously limits the application of magnesium alloys. How to effectively and reasonably improve the corrosion resistance of magnesium alloys has become one of the focuses of current application research. Improving the corrosion resistance of magnesium alloys can be carried out in two aspects: on one hand, starting from the magnesium alloy itself, developing a new type of magnesium alloy with excellent performance;on the other hand, improving the corrosion resistance and wear resistance of the magnesium alloy through effective surface treatment. Numerous research results have shown that the corrosion resistance of magnesium alloys can be improved by changing the chemical composition and microstructure of the alloys, but the density of magnesium alloys increases significantly with the addition of rare earth elements, which reduces the advantages of the application of magnesium alloys.In order to keep the low-density advantage of the magnesium alloy, the surface properties of the magnesium alloy can be changed by surface technology to improve its corrosion resistance. Ceramic coatings are widely used to improve the surface properties of materials due to their high hardness, good wear resistance, excellent oxidation resistance and heat resistance. In this study, three ceramic coatings were prepared on the surface of AZ31B magnesium alloy by plasma spraying method. By comparing the microstructure and properties of three ceramic coatings, it was revealed that the ceramic coating can greatly improve the corrosion resistance of the magnesium alloy. The internal reason provides experimental support and theoretical basis for expanding the application of plasma spraying technology in improving the surface corrosion resistance of magnesium alloys.Three kinds of ceramic coatings of Al2O3, Al2O3-13%TiO2 (AT13) and Al2O3-20%TiO2 (AT20) were prepared on the surface of AZ31B magnesium alloy by plasma spraying. The microstructure, porosity,bonding strength and electrochemical corrosion performance of ceramic layers were compared. The results show that the plasma sprayed ceramic coating has a typical layered structure, and the coating has good bonding strength and low porosity. With the increase of the amount of TiO2 added, the bonding strength of the ceramic coating increases, the porosity decreases, and the corrosion resistance increases. The self-corrosion potential of the AT20 coating is increased by 701 mV compared with the magnesium alloy matrix, and the self-corrosion current density is reduced by two orders of magnitude.The impedance is six times that of the substrate, and the AT20 coating has the best corrosion resistance. The electrochemical corrosion process of the ceramic coating appears as local corrosion of the layer and corrosion of the substrate and causes the layer to peel off the coating.In the spraying state,the three ceramic coatings prepared by the plasma spraying method can not form a good corrosion protection for the magnesium alloy. Although the corrosion resistance is improved during the electrochemical corrosion, the matrix corrosion at the interface between the coating and the substrate occurs, leading to the peeling of the coating from the substrate. Therefore, effective ways to improve the corrosion resistance of such ceramic coatings: increase the density of the ceramic layer and the bonding layer, cutting off the diffusion of the etching solution to the matrix material, and enhancing the corrosion resistance of ceramic layer itself.