| The cerium-based conversion coating on corrosion-resisting aluminum alloy (LF21) was studied in this dissertation. The electrochemical and chemical deposition technics were confirmed for the formation of conversion coatings, the properties of coatings were tested, and the formation process and conversion mechanism were also researched.The optimum processes of electrochemical deposition and chemical deposition were obtained by orthogonal experiments, and the properties of conversion coatings were measured. Both of these two conversion coatings were even, compact and had excellent adhesion with good corrosion-resistance. The hydrophilic angles of the conversion coatings were under30°.The performances of the conversion coatings on LF21by four pretreatment technologies were studied. By comparing the four different pretreatments of electrochemical deposition, the optimal pretreatment process was identified.The influence of assistant anodes on conversion coatings was studied. By comparion the conversion coatings made by C and Pb as assistant anodes, both of these two conversion coatings had perfect properties.Some studies on micro-mechanism were carried out. The conversion coatings observed by SEM, and three-phases during the formation processes of coatings was proposed. The cerium content in conversion coatings increased with the increase of coatings-formation time. The cracks in conversion coatings would be wider with the increase of cerium content, the coating-formation time and the thickness of coatings. The post-treatment in molybdenum after the electric or chemical deposition could weaken the cracks. |
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