Effects of Process Parameters on the Color of Hard Anodic Oxidation Film on 7075 Al Alloy

To ensure the uniformity and consistency of the color of the hard anodic oxidation film of 7075 aluminum alloy, 7075 aluminum alloy was chosen as the research subject in this study. Utilizing the design of experiments (DOE) analysis method, the impact of process parameters on the color of the hard anodic oxidation film of 7075 aluminum alloy was investigated. The effects of different oxidation temperatures (-6, -3, 0, 4, 8 ℃), different oxidation current densities (2, 4, 6 A/dm2), different sulfuric acid contents (150, 200, 230, 240, 250, 300 g/L), different film thicknesses (20～80 μm), and different loading positions on the color of the hard anodic oxidation film were tested. Results showed that as the temperature increased and the current density decreased, the color difference value of the oxide film gradually decreased. When the current density was 2 A/dm2, the temperature was maintained at 4 ℃ [with a control error of (4±1) ℃], the concentration of sulfuric acid was 200～230 g/L, the color of the oxide film closely matched that of the original sample. At a film thickness ranging from 20 to 80 μm, the color of the oxide film on the sample progressively darkened as the thickness increased, transitioning from light yellow to yellowish-brown and eventually to chocolate-brown. At a thickness of 80 μm, the film’s color changed to blue brick. Different loading positions had no significant effect on the color of the oxide film.