Effect of process parameters on the growth and microstructure of anodic films on 6061 aluminum alloy in alkaline electrolytes

This study investigates the anodizing of 6061 aluminum alloy using an alkaline solution composed of sodium hydroxide (NaOH), sodium tetraborate (Na₂B₄O₇) and potassium pyrophosphate (K₄P₂O₇). The effects of the electrolyte compositions as well as temperature and voltage on the growth and microstructure of anodic films were investigated. Results showed that all these parameters have effects on the current density of the anodizing process and thickness of the anodic films. The current density increases with process parameters except for Na₂B₄O₇, while as the process parameters increase, the anodic film thickness initially increases and then decreases. The morphology of the anodic film is notably affected by variables NaOH, Na₂B₄O₇, temperature, and voltage. Increasing NaOH concentration and temperature resulted in a decrease in surface uniformity, while Na₂B₄O₇ exhibited an opposite effect. Voltage significantly affected the diameter of the anodic film's pores, resulting in larger pores at higher voltages, which leading to poorer dyeing effect for the anodized samples.