铝合金表面钛锆转化膜的性能

Performances of Ti-Zr Conversion Coating on Aluminum Alloy

为开发出可替代铝合金表面铬酸盐转化工艺,以2024铝合金为基体,采用钛酸盐、锆酸盐为主盐,制备了金黄色与灰色2种无铬钛锆转化膜,并与阿洛丁铬酸盐转化膜进行性能对比。通过扫描电子显微镜(SEM)、能谱(EDS)、盐雾试验、动电位极化曲线和电化学阻抗谱对3种转化膜的表面形貌、成分、耐蚀性能及防护机制进行分析表征。结果表明:2种钛锆转化膜表面平整、无明显缺陷,但呈现出不同的微观形貌特征;经168 h中性盐雾试验,二者均无明显腐蚀产物产生;2种钛锆转化膜极化曲线呈现出较为明显的钝化区,膜层电阻也随浸泡时间的延长逐渐增加,但其模值|Z|要远低于铬酸盐转化膜,灰色钛锆转化膜的防护性能要优于金黄色钛锆转化膜。

Two novel chromium-free Ti-Zr conversion coatings(golden and gray) on 2024 aluminum alloy were prepared based on titanate and zirconate as precursors,which were compared with Rodin chromate conversion coating.The morphologies and composition of the coatings were determined with scanning electron microscopy(SEM) and EDS.Furthermore,the corrosion resistance of the coatings was investigated using potentiodynamic measurement,NSS test and AC impedance spectra,and the corrosion mechanism was analyzed.Results showed that both Ti-Zr conversion coatings were smooth and compact,without obvious defects.However,they presented different morphologies.Both golden and gray Ti-Zr conversion coatings had excellent corrosion resistance and there were no obvious corrosion products observed after 168 h salt spray test.Both the Ti-Zr conversion coatings presented obvious passivation region on the potentiodynamic curves,and the resistance of the coatings was increased gradually with the immersion time,whereas the |Z|was much lower than that of the chromate chemical conversion coating.Besides,the gray Ti-Zr conversion coating had better protection effect than the golden one.