多羟基化合物对6063铝合金表面钛锆转化膜的影响

Effect of polyhydroxy compound on titanium-zirconium conversion film on 6063 aluminum alloy surface

以6063铝合金为基材,研究了一种基于多羟基化合物的钛锆体系有机-无机复合转化处理体系。考察了该复合膜的膜重、沸水附着力、耐硝酸点滴腐蚀性能及其后续粉末涂料膜层的抗杯突、耐沸水和耐盐水性能,并与单纯钛锆转化膜及传统铬酸盐转化膜进行了比较。在质量分数为3.5%的NaCl溶液中通过极化曲线和电化学阻抗谱(EIS)分析了多羟基化合物的加入对6063铝合金表面钛锆转化膜耐蚀性的影响。采用扫描电镜(SEM)及能谱(EDS)表征了有机-无机复合转化膜的表面形貌及元素组成。结果表明:多羟基化合物的加入使钛锆转化膜由无色变成淡黄色,由疏松有孔的粒状结构变成致密少孔的层状结构,膜重有一定增加,沸水附着力及后续涂层的抗杯突、耐盐水性能更优异,耐腐蚀性能也有显著提高。该复合无铬转化膜层主要由C、O、Mg、Al、Ti、Si和Zr元素组成。

An organic-inorganic composite conversion system based on a conventionai Ti-Zr conversion bath with a polyhydroxy compound was studied using 6063 Al alloy as substrate. The weight, boiling-water adhesion, and HNO3 dropping corrosion resistance of the composite coating as well as the resistance of a subsequent powder coating prepared on it to cupping, boiling water, and salt water were tested and compared with those of the conventional Ti-Zr conversion coating and chromate conversion coating. The effect of the polyhydroxy compound on Ti-Zr conversion coating on 6063 Al alloy surface was examined by polarization curve measurement and electrochemical impedance spectroscopy （EIS） in 3.5wt% NaCl solution. The surface morphology and elemental composition of theorganic-inorganic composite coating were characterized by scanning electron microscopy （SEM） and energy-dispersive spectroscopy （EDS）. The results showed that the addition of the polyhydroxy compound changes the Ti-Zr conversion coating from a loose, granular, and porous microstructure with colorless appearance to a compact and laminar micro- structure with pale yellow appearance, results in increased coating weight and remarkably enhanced the adhesion strength in boiling water, corrosion resistance, as well as anti-cupping performance and salt water resistance of the subsequent powder coating. The Cr-free composite conversion coating is mainly composed of C, O, Mg, Al, Ti, Si and Zr.