Trace Gallium For High Voltage Anode Aluminum Foil Recrystallization Texture And Corrosion Hole Performance Impact

Anode aluminum foil is the key material for high voltage aluminum electrolytic capacitors which are one of the three basic electronic components. After years of development, the volume fraction of cube texture more than95%for domestic anode aluminum foil can be achieved steadily, but the foil’s surface enlarging ability in the environmental HCl-H2SO4corrosion system remains weak. In order to promote the surface enlarging ability and corrosion homogeneities of anode aluminum foil in HCl-H2SO4solution, the micro structure, recry stall ization cube texture and pitting morphology of the foils containing trace Ga were investigated on the basis of the effect of trace Ga on the electrochemical properties of high purity aluminum, using optical microscopy (OM), scanning electron microscopy (SEM) and electrochemical technique. The main results are as follows:(1) Trace Ga, as low as40ppm, added to high purity aluminum produces surface activation in chloride solution, shifting the open circuit potential and pitting potential to negative direction by about0.1-0.15V,0.12V respectively as the specimens annealed at500℃for lh. Naturally, the activation effect of40ppm Ga is weaker than0.5%Ga, and would be affected by heat treatment process.(2) Trace Ga, even as high as about80ppm, would not inhibit the development of strong recrystallization cube texture in aluminum foil. Actually, the cube texture of the foils containing Ga is as much as or even stronger than that of the normal foil manufactured within the same process. Thereinto, the volume fraction of cube texture is over95%for the foil containing20ppm Ga, and appears rise and fall but over90%with the increase of Ga content.(3) Gallium could segregate to the surface of aluminum foil after final annealing, which heightens the foil’s sensitivity for chloride ion and therefore improves its pitting ability in HCl-H2SO4corrosion system. Generally, the pitting potential of the foils containing Ga, annealed around540℃for less than2hours, shifts negatively to about-0.855V. Meanwhile, the ratio of corrosion area reaches about95%-98%, which is highly increased comparing to that of the normal foil. To be more specific, the pitting ability of the foil containing20ppm Ga is significantly improved as the initial pits are numerous, medium sized and uniformly distributed within the corrosion area; however, higher content of Ga about80ppm could induce a decrease in pitting ability as some large pits form in the corrosion area.(4) Comparing to some domestic commercial aluminum foil, the pitting ability of the foil containing20ppm Ga is highly improved as it shows a much higher rate of pit nucleation and propagation during DC-etching. At about30s, the ratio of corrosion area is over75%for the Ga-contained foil, while it’s less than10%for the domestic foil; at120s, nearly98%of the Ga-contained foil’s surface corrodes with enormous so-called fine pits in it. Moreover, NaOH+HCl co-pretreatment could improve surface quality of the Ga-contained foil, and therefore the pitting ability to the level of import commercial aluminum foil.