2024铝合金表面钒锆复合转化膜的制备及其性能

Prepartion of Vanadium /Zirconium Composite Conversion Coating on 2024 Aluminum Alloy Surface and Evaluation of Corrosion Resistance of the Coating

为克服2024铝合金表面单独钒盐或锆盐转化膜存在裂纹而导致其耐蚀性能不佳的问题,采用由氟锆酸钾、偏钒酸钠组成的转化液,在2024铝合金表面制备了钒锆复合转化膜。采用扫描电镜、能谱仪分析了复合膜的形貌及成分,采用中性盐雾试验和极化曲线研究了其耐蚀性能,采用百格法划格法研究了复合膜与基体的结合力及复合膜与漆膜的结合力。采用单因素法对转化液组分及转化条件进行了优选。结果表明:在2.0 g/L K2ZrF6,2.5 g/L NaVO3组成的转化液中,在pH值为3.0,温度为65℃的条件下反应20 min,所得钒锆复合膜致密、无裂纹,由O,F,Mg,Al,Zr,V,Cu等元素组成,膜基、膜漆结合较好,复合膜腐蚀电位较基体正移了86 mV,腐蚀电流密度减小为基材的1/5,耐蚀性能较基体明显提高。

A kind of conversion solution mainly consisting of potassium fluozirconate( K2ZrF6) and sodium metavanadate( NaVO3) was adopted to prepare vanadium /zirconium composite conversion coating on the surface of 2024 Al alloy so as to improve the corrosion resistance. The morphology and elemental composition of as-prepared composite conversion coating were analyzed by scanning electron microscopy and energy dispersive spectrometry. The corrosion resistance of the conversion coating was evaluated based on neutral salt spray test and measurement of potentiodynamic polarization curves. Moreover,the adhesion of the composite conversion coating to Al alloy substrate and varnish film was determined by scribing method. Results indicated that,after 20 min of conversion reaction in the conversion fluid composed of 2. 0 g /L K2ZrF6 and 2. 5 g /L NaVO3 at a pH value of 3. 0 and a temperature of 65 ℃,resultant vanadium /zirconium composite conversion coating was compact and free of cracks,and it consisted of O,F,Mg,Al,Zr,V,and Cu. Besides,as-prepared composite conversion coating exhibited good adhesion to Al alloy substrate and varnish film as well,while its corrosion potential was positively shifted by 86 mV and its corrosion current density was reduced to 1 /5 of that of the Al alloy substrate,showing greatly improved corrosion resistance.