目的 研究Mg元素含量对桥梁缆索钢丝微观组织及耐蚀性能的影响，在保证桥梁缆索强度要求的同时，进一步增强其耐蚀性能。方法 在450 ℃左右，在桥梁缆索钢丝表面热镀Zn-Al-xMg(x=0.5, 1.0, 1.5)镀层。使用扫描电子显微镜(SEM)以及能谱仪(EDS)研究镀层的组织结构特征。通过中性盐雾试验，表征钢丝Zn-5Al-xMg(x=0.5, 1.0, 1.5)镀层的腐蚀速率。用X射线衍射仪(XRD)探究镀层与腐蚀产物的具体成分。利用电化学工作站测试Mg元素含量变化时Zn-Al-Mg镀层的腐蚀行为变化规律。结果 Zn-5Al-xMg镀层组织主要由Zn-Al-MgZn2三元共晶相、富Zn相与少量富Al相组成。Mg元素的加入使得镀层的自腐蚀电流密度降低，促进了覆盖性优异且难溶的Zn5(OH)8Cl2.H2O的生成，阻止了镀层表面腐蚀后产生无保护性的ZnO，防止基体发生腐蚀。分析阻抗与中性盐雾试验结果可以发现，随着Mg元素含量的增加，Zn-5Al-Mg镀层的电化学交流阻抗值不断增大，腐蚀速率不断降低。结论 当Mg元素含量为1.5%(质量分数)时，Zn-5Al-xMg镀层的耐蚀性能最佳，Zn-5Al-1.5Mg镀层的耐蚀性能约为Zn-5Al镀层的2.4倍。

This work aims to study the influence of Mg element content on the structure and corrosion resistance of bridge cable wire, and to further improve the corrosion resistance of bridge cable wire on the basis of ensuring the mechanical properties of bridge cable wire. At about 450 ℃，hot dip plating method was used in steel wire surface and the Zn-Al-Mg coating was prepared. Electronic universal testing machine and torsion testing machine were used to investigate the strength and torsion performance of steel wire respectively. The microstructure of Zn-Al-Mg coating was addressed by scanning electron microscope (SEM) and energy spectrum (EDS). The phase composition of coating and corrosion products were analyzed by X-ray diffractometer (XRD). The coating corrosion resistance was represented by the neutral salt spray test. The corrosion behavior of Zn-Al-Mg coatings with different Mg content was studied by potentiometric polarization curve and electrochemical impedance spectroscopy. The results shows that the Zn-5Al-xMg (x=0.5, 1.0, 1.5) coating structure is mainly composed of ternary eutectic phase of Zn-Al-MgZn2, Zn-rich phase and a small amount of Al-rich phase. The addition of Mg element reduces the self-corrosion current density of the coating, promotes the generation of the protective corrosion product Zn5(OH)8Cl2.H2O, prevents the formation of the non-protective corrosion product ZnO, and effectively prevents the corrosion reaction from going into the alloy. Zn5(OH)8Cl2.H2O is a kind of dense and insoluble gel with good adhesion and low conductivity. When corrosion occurs, the coating will form a dense protective film on the surface of zinc alloy. Impedance and neutral salt spray test results also show that with the increase of Mg element content, the electrochemical ac impedance of Zn-5Al-Mg coating increases continuously, and the corrosion rate of neutral salt spray decreases continuously. The corrosion resistance of Zn-5Al-xMg coating achieved the best when Mg element content was 1.5wt%. And the corrosion resistance of Zn-5Al-1.5Mg coating was 2.4 times that of Zn-5Al coating.