Characteristics of Ce–Mn film on 6061 alloys and its improved performance

Abstract

HF2− was applied to accelerate the Ce–Mn film formation on 6061 Al alloy in the Ce3+–MnO4− solution. The process of film formation, the composition and structure of the film were analyzed by scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometer (XRD). The film formation process includes three stages. At the initial stage, a three-dimensional (3D) skeleton was formed quickly, and then the skeleton was fully filled with cerium oxide and manganese oxide, resulting in a dense structure. Subsequently, a new skeleton was formed and also filled. Al, Ce, O and Mn were detected in the film. Ce existed mainly in the form of Ce4+ (89%). The film existed in an amorphous form and was composed of ceria (cerium hydroxide), manganese dioxide and aluminum oxide. After electrostatically spraying fluorocarbon powder, the resultant products satisfied the required mechanical performance and exhibited almost non-filament corrosion compared with commercially available chromium-free conversion film. Its corrosion resistant time to acetate spray can reach 2000 h, which is consistent with that of fluorocarbon paint. The results showed that Ce–Mn film can offer an attractive prospect to eliminate volatile organic compounds (VOC) problem arisen by using fluorocarbon paint in the process of industrial production.