Automated color etching of aluminum alloys

Color metallography of aluminum alloys can provide new structural knowledge or extend and refine structural knowledge compared to a black and white image. The basic principle of color metallography is to create a suitable film by etching. On samples coated with a suitable film, light interference is caused by the splitting of the incident light into components reflected at the air-layer interface and the layer-metal interface. The thickness of the film essentially determines at which colors the interference occurs. For films of suitable thickness, interference occurs in the blue, green and yellow regions. The film thickness depends on the chemical composition of the sample material, the chemical composition of the etchant and the etching time. If the etching conditions are kept constant (etchant type, etching time) and the chemical composition of the individual micro-areas changes significantly, it will be possible to distinguish the microareas by color contrast in the bright field. The results of color etching of aluminum alloys in different types of etchants will be presented. Using an automated apparatus, the same etching conditions will be maintained, including time and repeatability of movements in the etching, cleaning and drying process.