Rui-Jun Zhang

Corrosion resistance, composition and structure of RE chemical conversion coating on magnesium alloy

Abstract Golden yellow rare earths chemical conversion coating was obtained on the surface of magnesium alloy by immersing in cerium sulfate solution. The corrosion resistance of RE conversion coating was evaluated using immersion test and potentiodynamic polarization measurements in 3.5% NaCl solution. The morphologies of samples before corrosion and after corrosion were observed by SEM. The structures and compositions of the RE conversion coating were studied by means of XPS, XRD and IR. The results show that, the conversion coating consists of mainly two kinds of element Ce and O, the valences of cerium are +3 and +4, and OH − exists in the coating. The anti-corrosion property of magnesium alloy is increased obviously by rare earths conversion coating, Its self-corrosion current density decreases and the coating has self-repairing capability in the corrosion process in 3.5% NaCl solution.

Influence of NaCl on dechromization of Cu-Cr-Al alloy in H3PO4 solution

Abstract The dechromization of Cu-Cr-Al alloys was investigated by a static immersing corrosion test. The influence of NaCl on the dechromization was analyzed by electrochemical test, scanning electron microscopy, optical microscopy and X-ray fluorescence spectroscopy. The results show that the dechromization of Cu-Cr-Al alloys will take place in a H3PO4 solution of 11.32 mol/L at 55 °C. And the corrosion process occurs initially at the interface between Cu and Cr phase, and then extends inward Cr-phase inside. The addition of NaCl into H3PO4 solutions can shorten the dechromization incubation time, decrease the dechromization temperature and concentration of H3PO4 solution, and increase the tendency of dechromization. But, the NaCl scarcely has an effect on the form and structure of chromium depleted-layer.

Microstructure evolution and thermal expansion of Cu-Zn alloy after high pressure heat treatment

Abstract The thermal expansion coefficients of Cu-Zn alloy before and after high pressure treatment were measured by thermal expansion instrument in the temperature range of 25-700 °C, and the microstructure and phase transformation of the alloy were examined by optical microscope, X-ray diffractometer (XRD) and differential scanning calorimeter (DSC). Based on the experimental results, the effects of high pressure treatment on the microstructure and thermal expansion of Cu-Zn alloy were investigated. The results show that the high pressure treatment can refine the grain and increase the thermal expansion coefficient of the Cu-Zn alloy, resulting in that the thermal expansion coefficient exhibits a high peak value on the α - T curve, and the peak value decreases with increasing the pressure.