Effect of chemical plating Zn on DC-etching behavior of Al foil in HCl-H2SO4

The Al foil for high voltage Al electrolytic capacitor usage was immersed in 5.0% NaOH solution containing trace amount of Zn2+ and Zn was chemically plated on its surface through an immersion-reduction reaction. Such Zn-deposited Al foil was quickly transferred into HCl-H2SO4 solution for DC-etching. The effects of Zn impurity on the surface and cross-section etching morphologies and electrochemical behavior of Al foil were investigated by SEM, polarization curve (PC) and electrochemical impedance spectroscopy (EIS). The special capacitance of 100 V formation voltage of etched foil was measured. The results show that the chemical plating Zn on Al substrate in alkali solution can reduce the pitting corrosion resistance, enhance the pitting current density and improve the density and uniform distribution of pits and tunnels due to formation of the micro Zn-Al galvanic local cells. The special capacitance of etched foil grows with the increase of Zn2+ concentration.