Low concentration chromate conversion technology was successively applied on hot dip Zn-Al alloy coating. The primary dissolution of the active Zn-rich phase within the coating immersed in the conversion solution associated with the evidence that the relative activities of each of the elements composing the Al-Zn coatings in the 0.5 mol/L H_ 2 SO_ 4 was Zn > Al > steel. XPS and AES analyses indicated that the chromate conversion film formed on the surface of the Zn-Al alloy coating consists of Cr(OH)_ 3 , Cr_ 2 O_ 3 , ZnO, Al_ 2 O_ 3 , and TiO_ 2 . The results of CASS test confirmed that the corrosion resistance of Zn-Al alloy coating was improved remarkably after the chromate conversion treatment. The fingding that corrosion, especially local corrosion of Zn-Al alloy coating is remarkably reduced may be attributable to the fact that the chromate conversion film in prohibits the anodic and cathodic reactions of the corrosion process, and improves the surface state of the Zn-Al alloy coating.
