Effects of Speeds, Voltages, and Electrolytes on Localized Surfaces of Al 6061 Alloys Anodized Using a Direct Writing Pen

Abstract

For many applications, aluminum alloys require anodization to produce alumina film that protects the surfaces against corrosion and abrasive wear. This process is often carried out traditionally, by dipping the substrate into a suitable bath of electrolyte. A study on the effectiveness of a direct writing pen for localized anodization of aluminum 6061 surface is presented. The writing pen is designed for applications in which complete submersion of the substrate in an electrolyte is inconvenient or unnecessary. Three aqueous electrolyte solutions were used: 15% (v/v) sulfuric acid; 10% (v/v) sulfuric acid plus 5% (v/v) citric acid; and 5% (v/v) sulfuric acid plus 10% (v/v) citric acid. Voltage levels of 30, 40, and 50 volts were applied, while the writing traverse speeds were 0.1, 1, and 3 mm/s on different experimental samples. The anodic oxide films were characterized for surface morphology, thickness, micro-hardness, and ability to hold dyes through the nanopores. The results show that the lower the pen traverse speeds, the higher the thickness of the alumina films produced. The thicknesses obtained were highest at 21.5 μm for oxide films generated at 0.1 mm/s traverse speed at 50V using sulfuric acid. However, the hardest surfaces were obtained for samples processed at 50V with two-pass anodization and 1 mm/s, yielding 596 Hv and softest for films with single pass anodization obtained at the 3 mm/s pen traverse speed with 40V. The direct write anodizing pen was found to demonstrate effectiveness for localized surface anodization that would be cost-effective in niche applications.