S355海洋钢表面微弧氧化复合膜层耐蚀性能

采用激光熔覆与微弧氧化技术相结合在海洋钢表面制备了复合膜层.运用扫描电子显微镜（SEM）、能谱仪（EDS）和X射线衍射仪（XRD）表征复合膜层的微观结构，采用极化曲线、电化学阻抗谱、腐蚀磨损实验和浸泡腐蚀实验等测试方法研究膜层在质量分数3.5%的NaCl水溶液中腐蚀行为，并与熔覆涂层和基体进行对比.结果表明:复合膜层主要分为内致密层和外疏松层，疏松层主要由γ-Al₂O₃组成，致密层主要由α-Al₂O₃组成，与基底层结合较好，复合膜层表面硬度最大能达到HV_0.2 1423.3，比熔覆涂层高47.6%，其硬度较S355海洋钢有显著提升.基体在腐蚀和磨损交互作用中主要以腐蚀加速磨损为主，涂层在交互作用中主要以磨损加速腐蚀为主，在经过微弧氧化处理后，膜层的自腐蚀电位负移，钝态电流密度上升，抗磨蚀性能明显提高.熔覆涂层的浸泡腐蚀方式以点蚀为主，复合膜层腐蚀较轻微，阻抗模值最大能达到105.3 Ω·cm2，比熔覆层提高两个数量级，这表明复合处理可进一步提高涂层的耐腐蚀性. 

Corrosion resistance of micro-arc oxidation composite coatings on S355 offshore steel

Composite coatings were prepared by laser cladding combined with micro-arc oxidation technique on the surface of S355 offshore steel, and the composite coating structures were analyzed using scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. The corrosion behavior of the composite coating in 3.5% NaCl solution was investigated by polarization curve, electrochemical impedance spectroscopy, corrosive wear test, and immersion corrosion test, and compared with that of the cladding layer and substrate. The results show that the composite coating is mainly divided into inner dense layer and outer loose layer. The loose layer is mainly composed of γ-Al₂O₃, and the dense layer is mainly composed of α-Al₂O₃, and the surface hardness of the composite coating reaches the maximum value of HV_0.2 1423.3, which is 47.6% higher than that of the cladding coating. Moreover, the surface hardness of S355 offshore steel is significantly improved. The interaction between corrosion and wear in the substrate is mainly corrosion-accelerating abrasion, whereas that in the coating is wear-accelerating corrosion. After micro-arc oxidation treatment, the corrosion potential of the composite coating moves negatively, the passive current density increases, the scale factor of wear-accelerated corrosion gradually decreases, and the corrosive wear resistance of the coating significantly improves. The immersion corrosion method of the cladding coating is mainly pitting corrosion, the composite coating is slightly corroded, and the maximum impedance modulus reaches 105.3 Ω·cm2, which is two orders of magnitude higher than that of the cladding coating. This finding indicates that the corrosive wear resistance of the coating can be further improved after composite treatment.