The corrosion behaviors of hot-dip 55% Al-Zn alloy coating and Zn coating steel sheets in salt solution were comparative studied by salt spray corrosion test and immersion corrosion test. The corrosion mechanism of two kinds of coating was analyzed by electrochemical impedance spectroscopy (E1S). The appearance characters of steel sheet surface, where the corrosion products were eliminated, were observed by optical microscope ( OM ) and scanning electron microscope ( SEM). The result of salt spray corrosion indicated that the corrosion resistance of hot-dip 55% Al-Zn alloy coating was twice as that of hot-dip Zn coating in the same corrosion period of 288 h. During the initial stage of corrosion, the corrosion process of hot-dip 55% Al-Zn alloy coating steel sheet was controlled by the surface diffusion, but during the final stage of corrosion, the controlling step was the charge transfer through the steel sheet surface. The consequence of hot-dip Zn coating was just opposite to hot-dip 55% Al-Zn alloy coating.%用盐雾腐蚀和浸泡腐蚀两种方法对比研究了热浸镀55％ Al-Zn镀层和Zn镀层在盐水环境中的腐蚀行为.用光学显微镜和扫描电子显微镜观察了清除腐蚀产物后镀层表面组织和横截面形貌特征.热浸镀55％ Al-Zn镀层在盐雾腐蚀288 h时的失重率约为Zn镀层的1/2,说明55％ Al-Zn镀层具有更好的耐蚀性.用电化学阻抗谱方法分析镀层的腐蚀机理,认为55％ Al-Zn镀层腐蚀前期由扩散控制,后期由于极化电阻的减小,电荷转移增多；而Zn镀层腐蚀前期是由于极化电阻减小,电极表面以电荷转移过程为主,后期表现出扩散特征.
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