Characterization of calcium-modified zinc phosphate conversion coatings and their influences on corrosion resistance of AZ31 alloy

SURFACE & COATINGS TECHNOLOGY

卷:205

Article

Zeng, Rongchang^1,2  Lan, Zidong²  Kong, Linghong²  Huang, Yuanding³  Cui, Hongzhi¹ 

[1] Shandong Univ Sci & Technol, Coll Mat Sci & Engn, Qingdao 266510, Peoples R China

[2] Chongqing Univ Technol, Sch Mat Sci & Engn, Chongqing 400050, Peoples R China

[3] GKSS Forschungszentrum Geesthacht GmbH, MagIC Magnesium Innovat Ctr, D-21502 Geesthacht, Germany

关键词: Phosphate conversion coating;    Magnesium alloy;    Corrosion;    Calcium;    Zinc;   

DOI  :  10.1016/j.surfcoat.2010.11.027

来源: Elsevier

【 摘 要 】

Two kinds of phosphate conversion coatings, including zinc phosphate coating and zinc-calcium phosphate coating, were prepared on the surface of AZ31 alloy in phosphate baths. The morphologies of these coatings were observed using scanning electron microscopy. Their chemical compositions and structures were characterized using energy-dispersive X-ray spectrum, X-ray photoelectron spectroscopy and X-ray diffraction. The corrosion resistance of the coatings was evaluated by potentiodynamic polarization technique. The results show that the flowerlike Zn-Ca phosphate conversion coatings are mainly composed of hopeite (Zn-3(PO4)(2)center dot 4H(2)O). They have a quite different morphology from the dry-riverbed-like Zn phosphate coatings that consist of MgO, MgF2, Zn or ZnO and hopeite. Both of the zinc and zinc-calcium phosphate coatings can remarkably reduce the corrosion current density of the substrates. The Zn-Ca coating exhibits better corrosion resistance than the Zn coating. Introduction of calcium into the phosphate baths leads to the full crystallinity of the Zn-Ca coating. (C) 2010 Elsevier B.V. All rights reserved.

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