纳米微粒增强水性无铬锌铝合金涂层的制备及其性能

摘要

针对水性无铬锌铝合金涂层硬度低的问题,采用向涂液中添加硬质纳米颗粒的方法分别制备了SiO2、TiO2、ZnO、Al2O3和TiC纳米颗粒增强锌铝合金涂层,利用显微硬度测试和Tafel曲线研究纳米颗粒种类及含量(质量分数)对涂层硬度和腐蚀性能的影响,并采用电化学阻抗谱技术研究优化涂层的电化学腐蚀行为.结果表明:在不影响涂层腐蚀性能前提下,添加1％纳米ZnO的锌铝合金涂层综合性能最好,显微硬度从132.8 HVo.025提高到175.0 HVo.025,而自腐蚀电流密度仅从3.124 μA/cm2增至3.157 μA/cm2.纳米ZnO增强涂层在3.5％ NaCI溶液中的腐蚀过程经历4个阶段:一是初期涂层本身的屏蔽作用;二是涂层中金属粉的活化腐蚀阶段;三是腐蚀介质到达涂层-基体界面时涂层的阴极保护作用;四是后期腐蚀产物的物理屏蔽作用.%Zn-Al alloy coatings reinforced by SiO2,TiO2,ZnO,Al2O3 or TiC nanoparticle were prepared by adding hard nanoparticles to the coating solution to increase the hardness of water-based chrome-free coating,respectively.Microhardness testing and Tafel plots were used to study the influence of the type and content of nanoparticles on the microhardness and corrosion resistance of the coating.The electrochemical corrosion behavior of the optimized coating in 3.5％NaCl solution was studied by electrochemical impedance spectroscopy.The results show that Zn-Al alloy coating with addition of 1％ ZnO nanoparticles exhibites the best comprehensive performance without degradation of the corrosion performance.The microhardness of the coating increases from 132.8 HW0.025 to 175.0 HV0.025,while the corrosion current density only increases from 3.124 μA/cm2 to 3.157 μA/cm2.The corrosion process of the coatings reinforced by ZnO nanoparticles in 3.5％NaCl solution goes through four stages:① the shielding effect of the coating itself initially;② the activation corrosion of metal powders in the coating;③ the sacrificial anode protection of the coating when the corrosive medium reaches the coating/substrate interface;④ the physical shielding effect of the corrosion products lately.