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Tri-metallic galvanic corrosion is inevitable in practical applications, but relevant investigations are far from sufficient. In this study, a mathematical model based on the Butler-Volmer equation and a finite element model (FEM) of tri-metallic galvanic corrosion were built and validated, which can reasonably predict galvanic corrosion of tri-metallic couples. Simulation and experimental results indicate that galvanic current density and galvanic potential of the tri-metallic couple of 2024 aluminum alloy/Q235 carbon steel/304 stainless steel change with the cathode/anode area ratios in a power function relationship and logarithmic relationship, respectively in 3.5 wt% NaCl. Besides, galvanic corrosion not only accelerates the dissolution of 2024 Al alloy but also transforms its corrosion form. The uncoupled 2024 Al alloy presents pitting corrosion, but the coupled 2024 Al alloy shows typical intergranular corrosion (IGC) morphology.

Self-healing coatings can inhibit the corrosion of Mg alloys from the damaged areas. In this paper, a duplex self-healing coating, with loading interphase inhibitor into the pores of micro-arc oxidation (MAO) film and doping organic inhibitor into the top paint, is prepared to enhance the self-healing property. The synergistic effect between both inhibitors and the self-healing property of the coating were characterized. The releasing and healing processes were investigated. The results show that 2-mercaptobenzothiazole (MBT) can absorb on the defects of the formed Mg3(PO4)2 and Mg(OH)2 film, which further inhibits the corrosion process by synergistic effect. When the self-healing coating is damaged, phosphate ions can be released from the MAO film quickly while MBT is released from the top paint slowly, then they synergistically inhibit the corrosion of the damaged areas, enhancing the self-healing property greatly in comparison with addition of each inhibitor singly.

The influence of the quantity of the Mg(2)Sn phase on the corrosion behavior of different solution temperature treated Mg-7Sn magnesium alloy has been investigated by electrochemical measurements, scanning electron microscope (SEM) observation, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. With the increase of solution temperature, the quantity of Mg(2)Sn phase decreased and the tin concentration of matrix increased. The dissolved tin in Mg matrix took part in the film formation and the constituent of film was magnesium oxide and stannic oxide. The corrosion mode and corrosion rate were associated with the quantity of Mg(2)Sn phases and tin concentration of the matrix. If most of tin was present as Mg(2)Sn, the corrosion mode was pitting corrosion and it accelerated the corrosion rate. If most of tin was dissolved in matrix, the corrosion mode was filiform corrosion and it decreased the corrosion rate. The experiment evidences demonstrated that the corrosion resistance can be improved by increasing the tin concentration of matrix and the lowest corrosion rate was observed for sample solution treated at 540 degrees C. (C) 2010 Elsevier Ltd. All rights reserved.