Chrome-free Fridge Freezers Evaporation Used Aluminum Tubes Online Passivation

The chromium-free online passivating technology of aluminium tube used for evaporator in refrigerator and freezer was studied in this paper. According to orthogonal design test method, the optimal formula of organic collaborative passivation were obtained as:the concentration of vinyl-tri-(β-methoxyethoxy)silane, organic acid ester DP and ethanol, was 50 ml/L,5 g/L and 50 ml/L, respectively, where the pH of passvation solution was adjusted to 2.0 and the reaction time was 1 h. As the single factor experiment results showed, the optimal processing parameters were: passivation temperature 40℃, passivation time 20 s, curing temperature 100℃and curing time 1 h. It was found that the passivation efficiency could be increased significantly by adding 1.5 g/L nano SiO2. Then, the organic doping passivation aluminum tube (reduced as doping passivation tube) could be obtained after a series of operations at the suitable conditions showed above.According to bluestone drips test, hydrogen evolution test and salt spray test, doping passivation tube was recommended for its good corrosion resistance, better than that of conventional chromate passivation tube. As the electrochemical results showing, obtained from the Tafel polarization curves and electrochemical impedance spectroscopy (EIS), the resistance of Al was enhanced significantly and corrosion current density was obviously decreased, which inhibited the occurrence and development of electrochemical corrosion reactions on Al substrate were inhibited effectively. And the corrosion rate of Al was obviously decreased. The surface structure was analyzed by metallographic microscope and scanning electron microscope (SEM). It was found that the surface of doping passivation film with high coverage was dense, uniform and smooth. Atomic force microscope (AFM) analysis results indicated that the doping passivation film formed with a large number of amorphous solid particles reached to a certain thickness. Energy dispersive spectroscopy (EDS) showed that the doping passivation film mainly consisting of Al, C, O, Si and P elements. The film formation and corrosion resistance mechanism of the doping passivation tube was also discussed.Industrial experiment indicated that the passivation formulation and process satisfied the online passivation production requirements of Canform continuous extrusion aluminum tubes well. The corrosion resistance, bending performance and adhesion of industrial passivation aluminum tube were met with the requirements of aluminum tube used for evaporator in refrigerator and freezer. Meanwhile, the formula of the passivation solution is environmental friendly. With the low passivation temperature, short passivation time, simple process, this technology could be used as a novel and promising passivation way to replace the traditional chromate passivation, which suggested a promising and bright future.