镀锌钢板蒸镀镁层的耐腐蚀机理

Anticorrosive Mechanism of Vapor Deposited Mg Coating on Galvanized Steel Sheets

采用真空蒸镀技术在镀锌钢板上蒸镀镁,制得了蒸镀镁层,将其在5%NaCl溶液中浸泡,运用XRD,SEM和电化学方法等对其腐蚀产物进行了分析。对2种材料的的腐蚀行为进行了研究,探讨了其耐腐蚀机理。结果表明:镀锌钢板蒸镀镁层是以MgZn2和Mg2Zn11金属间化合物的形式存在;其腐蚀产物是以致密且具有良好绝缘性的ZnCl2.4Zn(OH)2.H2O和致密的Zn4CO3(OH)6.H2O为主体,而纯锌镀层的腐蚀产物是以疏松且具有N型半导体性质的ZnO为主体;蒸镀镁层的形成可以抑制Zn(OH)2向ZnO的转化,能促进Zn(OH)2向ZnCl2.4Zn(OH)2.H2O和Zn4CO3(OH)6.H2O的转化,后二者能够牢固地覆盖在基体表面,从而延缓了锌的腐蚀进程;在宏观上表现为镀锌钢板蒸镀镁层腐蚀产物相对于纯锌镀层更加致密,在电化学行为上表现为镀锌钢板蒸镀镁层具有更小的腐蚀电流和更高的极化电阻。

Mg coating was pre-pared on the surface of galvanized steel sheets by using vapor deposition in vacuum. The resulting vapor deposited Mg coating was immersed in aqueous solution of 5% NaCl. An electrochemi-cal test rig was performed to evaluate the corrosion behavior of the Mg coating. The composition and microstructure of the Mg coating were analyzed by means of X-ray diffraction and scanning electron microscopy,and the anticorrosive mechanism of the coating was explored. It was found out the vapor deposited Mg coating on gal-vanized steel sheets was mainly composed of intermetallics MgZn2 and Mg2Zn11.Compact and insulative ZnCl2.4Zn(OH)2.H2O and compact Zn4CO3(OH)6.H2O were the dominant corrosion products of the vapor deposited Mg coating,differing from the corrosion product of galvanized steel-loose amorphous ZnO with semi-conducting nature. At the same time,the vapor deposited Mg coating on galvanized steel sheets was able to retard the trans-formation from Zn(OH)2 to ZnO and accelerate the transformation from Zn ( OH )2 to ZnCl2.4Zn(OH)2.H2O and Zn4CO3(OH)6.H2O,and the latter two compounds could be well adhered on the surface of substrate,hence retarding corro-sion. Moreover,from a macro-perspective,the corrosion prod-ucts of vapor deposited Mg coating on galvanized steel sheets were more compact than that of conventional galvanized steel,while in terms of electrochemical behavior,the vapor deposited Mg coating had a smaller corrosion current density and higher polarization re-sistance.