Preparation And Performance Study On Rare Earth Passivation Films Of H62 Copper Alloys

Chromate passivation of copper has been prohibited gradually because of appeal from enmronment protection, but aciduric and alkali-resistant of passivation films of the BTA and its ramification is weak. The rare earth salt associate with BTA is applied to surface treatment of copper. By studying the composition of passivation solution, temperature and time and by orthogonal design, the optimization passivation technics is proposed. Rare earth passivation films were obtained on surface of copper by immersion process.By analyzing the results of orthogonal design, obtain the influence of composition of passivation solution, temperature and time on the performance of passivation films. And the influence of rare earth salt is the most important. The corrosion resistance of passivation films is studied by nitric acid drop test, moisture/heating test, salt spray test and weight lose method and compared with the optimal passivation technics without rare earth salt. And study the corrosion behavior of the sample after passivation by rare earth salt in 3.5%NaCl.The corrosion resistance of passivation films is analyzed ulteriorly by Anodic polarization curves and EIS impedance measurements. The composition, structure and morphologies of coating were identified by X-ray diffraction analysis (XRD), Electron microprobe analysis (EMPA) and SEM (electron microscope).The composition of films was analyzed by Raman spectra.The corrosion resistance mechanisms of passivation films are lucubrated.In a word , The appearance of H62 copper alloys treated by the optimization passivation technics is golden, colour and luster is uniform.The scanning microscopic examination indicated that the passivation films formed on the copper alloys are homogeneous . The passivation films can endure nitric acid drop for 20s or can anti-discolour in 48h in moisture/heating test or can anti-discolour in 12h in salt spray test. The corrosion rates of rare earth passivation films in 3.5% NaCl or sea water reduced greatly. The technological process is so simple that the unfamiliar operators can manipulate it. Furthermore, the consumption of expenses is small during passivation process. The passivation solution is stable and does not decompound in some days, and process can become simpler based on the fact. Accordingly, it is a kind of perfect chromate-free passivation technique and can solve the problem that chromate passivation is prohibited gradually but no equal substitute technique. It has promising prospect in industrial applications.