氟钛酸钾添加对铝镁复合板微弧氧化涂层结构及耐蚀性的影响

为研究氟钛酸钾(K₂TiF₆)添加对Al-Mg复合板微弧氧化涂层结构和耐腐蚀性能的影响，在硅酸盐-氢氧化钠电解液体系中加入不同浓度的氟钛酸钾(0、1、2和3 g·L^-1)，利用微弧氧化技术(MAO)在Al-Mg复合板表面制备陶瓷氧化物涂层。通过SEM、XRD、EDS和电化学工作站等对制备陶瓷氧化物涂层显微组织、相组成、形貌及耐蚀性能进行表征。添加K₂TiF₆后，Al-Mg复合板Al侧的涂层厚度、表面孔隙率和表面粗糙度随K₂TiF₆浓度的增加呈下降的趋势(24.2～18.4μm、6.8%～5.3%、3.55～2.23),Mg侧涂层呈上升趋势(21.0～26.6μm、3.6%～5.3%,3.35～4.33)，此外涂层中的Ti和F元素含量增加，各样品的耐蚀性均有所提高。添加K₂TiF₆为2 g·L^-1时，两侧涂层的耐蚀性最好，其中R_t均比未添加的样品增加...

Effect of K2TiF6 Concentration on Microstructure and Corrosion Resistance of Al-Mg Composite Plate Based Micro-arc Oxidation Coatings

Micro-arc oxidation (MAO) can form an in-situ ceramic oxide film on the valve metal surfaces of Al and Mg, and it is a surface treatment method for Al-Mg composite plates. In the MAO process, different additives or different concentrations of the same additive added to the electrolyte can affect the MAO behavior, film microstructure, and corrosion resistance of the coatings. To explore the influence of K2TiF6 concentrations on the microstructure and corrosion resistance of Al-Mg composite plate-coating-based MAO coatings, in this paper, MAO was applied to deposit ceramic oxide coatings on Al-Mg composite plates with different concentrations K2TiF6 addition (0, 1, 2, and 3 g center dot L-1) in the NaSiO3-NaOH electrolyte. The MAO behavior, coating structure, and corrosion resistance of the Al-Mg composite plate coating with 40 min of oxidation were studied. The micromorphology and phase structure composition of the Al-Mg composite plate ceramic oxide coatings were analyzed using SEM, XRD, XPS, EDS, and 3D surface profilers. The corrosion resistance of the coating was studied using an electrochemical workstation and a salt-mist corrosion tester. The addition of K2TiF6 increased the breakdown voltage and discharge intensity of the Al-Mg composite plate, thereby promoting the growth of coatings on both sides of the composite plate and increasing the number of defects. The coating in the contact region of the welding surface was continuous and tightly bonded, indicating that the composite plate was protected by the coating. The coatings on the Al side were mainly composed of gamma-Al2O3 and mullite phases, while the Mg side coatings were all composed of MgO and Mg2SO4 phases. After the addition of K2TiF6, the Ti and F contents in the ceramic oxide coating increased, and the corrosion resistance was enhanced in all samples. These characteristics of coating thickness, surface porosity, and roughness on the Al side of Al-Mg composite plate showed a decreasing trend with the increase of K2TiF6 concentration, namely, its thickness decreased from 24.2 to 18.4 mu m, surface porosity from 6.8% to 5.3%, and roughness from 3.55 to 2.23. On the contrary, the thicknesses, surface porosity and roughness of Mg side coating increased when the concentrated K2TiF6 was added, the coating thickness increased from 21.0 to 26.6 mu m, surface porosity from 3.6% to 5.3%, and roughness from 3.35 to 4.33. These phenomena are mainly due to the energy transferring to the Mg side in the course of the micro-arc oxidation of the Al-Mg composite plate. After adding 2 g center dot L-1 K2TiF6, both Al and Mg side coatings of the Al-Mg composite plate samples showed the best corrosion resistance, in which Rt increased by two orders of magnitude compared with those for the unadded samples, and icorr decreased by one order of magnitude. After immersing the composite plate with this coating in a 3.5 wt.% NaCl solution for 126 h, the corrosion weight loss per unit area of the sample with 2 g center dot L-1 K2TiF6 was the least, approximately 1.08 mg center dot cm(-2). Nevertheless, it was merely 0.40 mg center dot cm(-2) lower than that of the sample without K2TiF6, which was related to the large-size holes formed in the coating under high breakdown energy. The addition of K2TiF6 could transform the microstructure of MAO coatings on the Al-Mg composite plate and improve its corrosion resistance. This can provide innovative ideas for the development of composite plate MAO coatings with high corrosion resistance. Keywords: K2TiF6; micro-arc oxidation; coating microstructure; corrosion resistance