Effect Of Trace Element Sn, Bi, In On The Electrochemical Behavior And Pitting Performance Of High Voltage Anode Aluminum Foil

In order to promote the electrochemical activity and corrosion homogeneities of high purity anode aluminum foil in HC1-H2SO4solution, the microstructure, electrochemical properties and pitting morphology of the foils containing trace Sn, Bi and In were investigated, by using CHI660C electrochemical workstation, Image J, MX-3000optical microscopy and Quanta-200scanning electron microscopy. The main conclusions are as follows:(1) Trace element Sn, Bi and In added to high purity aluminum with parts per million (ppm) produces surface activation in chloride solution, shifting the open circuit potential and pitting potential to negative direction, laying an experimental foundation for high voltage anode aluminum foil with excellent corrosion property.(2) Sn, Bi and In could segregate to the surface of aluminum foil after final annealing, the higher of the annealing temperature, the better of its segregation, therefore improves its electrochemical activity in HCl-H2SO4corrosion system.(3) ppm level of trace elements of Sn, Bi and In can improve the performance of high voltage anode aluminum foils of the corrosion properties. Comparing to the high purity aluminum foil without trace element, when adding the content of trace elements is5ppm, the pitting corrosion area is more than85%, when the content of trace elements is18ppm, high purity aluminum foil pitting corrosion area area is more than90%. The pitting performence of the foil containing trace element Sn, Bi, In is significantly improved as the initial pits are numerous, medium sized and uniformly distributed within the corrosion area.(4) Final annealing has a significant impact on the pitting performance of aluminum foils containing Sn, Bi and In. When the trace element is in the same content, in the condition of480℃annealing, high purity aluminum foils does not reach the equilibrium segregation concentration, and the elements segregate mainly to the defective regions, causing poor corrosion performence of aluminum foils. With the increase of annealing temperature up to560℃, the pitting regions of three kinds of samples reach more than90%, and the initial pits are numerous, medium sized and uniformly distributed within the corrosion area.(5) When the content of the trace elements and the annealing heat treatment are under the same condition, aluminum foils containing Sn show the most outstanding performance of corrosion property, Bi takes the second place. That is to say, Sn, relative to other two elements, could increase the electrochemical activity and improve the pitting performance of high purity aluminum foils at the most extent.