Analysis of corrosion products of zinc-aluminum-magnesium coating in 3.5％NaCl solution
The corrosion products on the surface of zinc-aluminum-magnesium coating,which was soaked in 3.5％NaCl solution for different periods(0 d,3 d,7 d,and 21 d),were investigated in depth be means of various analysis techniques including scanning electron microscopy(SEM),X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS).The results showed that the surface of normal zinc-magnesium-aluminum coating mainly contained Zn,Mg,Al and a small amount of C and O elements,which were composed of white blocky Zn-rich phase and gray eutectic structure(MgZn2 phase and Al-rich phase).There was an extremely thin oxide film on the surface.After corrosion by 3.5％NaCl solution,the contents of Zn,Mg and Al on the surface of zinc-magnesium-aluminum coating decreased obviously,while the contents of Fe and O increased significantly.As the corrosion time ranged from 3dto7dto21d,the surface of corrosion layer showed the color change from gray to white to orange yellow(deep red was observed when the corrosion was severe).The initial corrosion products were mainly Mg(OH)2 and Zn5(CO3)2·(OH)6.With the increase of corrosion time,the corrosion products were mainly AlFeO3,Zn5(CO3)2·(OH)6 and a small amount of Zn5(OH)6Cl2·H2O.When the corrosion time further increased to 21 d,the corrosion products were mainly FeO(OH)and a small amount of Zn5(OH)6Cl2·H2O.
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