Recent Developments in Black Finish Coatings on Aluminum Alloys by Keronite Plasma Electrolytic Oxidation

摘要

Coating application by electrolytic methods such as anodizing has been widely used for improving the wear and corrosion resistance of aluminum alloys. The porous nature of anodized coatings allows production of colored coatings such as black finish by deposition of organic dyestuffs. While black anodizing by organic color dyeing has been widely used to date, this technology is considered not to be fully environmentally safe because of handling and disposal issues. In addition, the organic dye stuff degrades upon exposure to UV radiation that is experienced by external parts.Matte black finish coatings with improved resistance to environmental exposures such as corrosion, humidity, scratch wear and UV degradation are of high interest for a number of exterior and interior applications, e.g., auto body and trim parts, optical instruments, and include defence objects which require low reflectivity. The Keronite Plasma Electrolytic Oxidation (PEO) is an environmentally safe electrolytic coating process that is applicable to light metals and their alloys, in particular Al and Mg. The Keronite process involves creation of a hard ceramic oxide layer on the surface of a light metal alloy by plasma oxidation of the substrate alloy in a proprietary solution that is environmentally safe. More recently, Keronite International Ltd has developed a matte black finish ceramic coating applicable to most aluminum alloys.In this paper, a matte black Keronite PEO coating on AA6060 alloy was studied. Coating microstructure was examined and the coating characteristics such as surface roughness, uniformity, hardness, porosity and phase composition were identified. The resistance of the black PEO coating to environmental exposures such as salt fog, thermal shock, UV-degradation and scratch wear were assessed. The reflectance and color analysis of the coating were also investigated.