Black anodic coatings for space applications: Study of the process parameters, characteristics and mechanical properties

Black inorganic anodized aluminium alloys are used for managing passive thermal control on spacecraft and for avoiding stray light in optical equipment. Spalling of these coatings has sometimes been observed after thermal cycling on 2XXX and 7XXX aluminium alloys. This phenomenon could generate particulate contamination in satellites and may affect mission lifetime. In this work, the influences of the four main steps of the process (pretreatments, sulphuric anodizing, colouring and sealing) on the coating characteristics have been studied for a 7175T7351 aluminium alloy. The chemical heterogeneity of the coating has been underlined, and its mechanical behaviour observed through crazing. Scratch-testing, used to evaluate coating adhesion to its substrate, revealed the negative impact of thermal cycling.