Effects of boric acid on microstructure and corrosion resistance of boric/sulfuric acid anodic film on 7050 aluminum alloy

The microstructure and corrosion resistance of different boric/sulfuric acid anodic (BSAA) films on 7050 aluminum alloy were studied by atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS) and scanning Kelvin probe (SKP). The results show that boric acid does not change the structure of barrier layer of anodic film, but will significantly affect the structure of porous layer, consequently affect the corrosion resistance of anodic film. As the content of boric acid in electrolyte increases from 0 to 8 g/L, the resistance of porous layer (Rp) of BSAA film increases, the capacitance of porous layer (CPEp) decreases, the surface potential moves positively, the pore size lessens, and the corrosion resistance improves. However, the Rp, CPEp and surface potential will change towards opposite direction when the content of boric acid is over 8 g/L.