Effect Of Annealing Process On Texture And Etching Area-enlarging Of High Voltage Anode Aluminum Foils

The high capacitance of aluminum electrolytic capacitors, are widely used in electronic components. At present, the capacitance of the anode aluminum foils used in high voltage electrolytic capacitors is determined by its surface area. In order to increase the surface area, the cube texture contents and the structure must be improved. The method of DC electrochemical etching is usually adopted for increasing specific capacitance of high voltage anode aluminum foils. In this paper, the intermediate annealing and final recrystallization annealing were investigated to increase the volume fraction of cube texture. Electrochemical pitting and tunnel-widening had been researched to obtain the large surface area of etched foils. It is expected that this work can give theoretical and technical support to the development of fully domestic high voltage anode aluminum foil.The microstructure, evolution of textures and electrochemical etching was investigated with analytical techniques such as optical microscopy (OM), X-ray diffraction (XRD), electron back-scattered diffraction (EBSD), scanning electron microscopy (SEM), electrochemical impedance spectrum (EIS). As the result, annealing process parameters and DC electric etching comprehended conditions were obtained in high voltage anode aluminum foils.The results indicated that higher temperature of the intermediate annealing led to larger size of grains and the faster of recrystallization rate of cold rolled aluminum sheets. After 350℃/2h annealing, the volume fraction of cube texture was 20% of the aluminum sheets. The structure became more homogeneous, and the deformation resistance was very weak. The cold rolled foils which were component of more S texture, Copper texture and about 10% cube texture could get more cube texture after annealed.The results indicated that the content of the cube texture during recrystallization annealing had relationship with annealing temperature, heating time and annealing process. Increasing annealing time and improving annealing temperature, the volume fraction of cube texture could increase. After 240℃/1h+540℃/1h annealing, the volume fraction of cube texture could reach 97%, while the mechanical and etching corrosion property could also meet the requirements.The formation mechanism and the evolution of cube texture was discussed in this paper. Cube texture is transformed from deformed textures (S, Copper) during discontinuous recrystallization process. The result showed that the evolution of cube texture was controlled by the combination of oriented nucleation and oriented growth.Pit etching experiments showed that temperature had the greatest influence on static capacity, followed by electrolyte components and etching time and the last one was current density. A preferable technology for pit etching was:80℃, lmol/LHCl+2mol/LH2SO4 of hot solution,0.6A/cm2 current density and etching 60s.Tunnel-widening (for increasing diameter and depth of tunnels) experiments showed that the Al3+ in electrolyte mainly affected on the density of pits, no the corrosion surficial area. The specific capacitance of aluminum foils was higher when strength of Al3+ was 1%. Along with the increasing strength of Al3+, the specific capacitance increased and then decreased. Extending the etching time can effectively enhance the specific capacitance. The capacitance was very large when the etching was 450s. As the result, the parameters were 3.5%HCl+1%Al3+, current density 0.1 A/cm2, time 450s and temperature 75℃. The surficial area, tunnels diameter and the specific capacitance could meet the requirement of high voltage anode aluminum foils.