Analysis of surface defects of aluminium components with hard anodized layers

•Identification of the cause of the defects on aluminium component with hard anodized layer.•Prove of the presence of the major defect prior to the beginning of the process of anodizing.•Identification of defect as a HOT CRACK, which was formed during primary foundry processes. Final quality inspection regularly reveals surface defects on components after hard anodizing. The aim of the analysis was to identify the cause of the defects and unambiguously determine whether the defect is caused by the quality of the base material, manufacturing technology of the component, the heat treatment or by the final surface treatment technology (anodizing). Analysis of the chemical composition and hardness measurements were performed to eliminate the possibility of any errors during material selection and heat treatment process. The capillary test revealed two major defects and also small amount of minor defects. To determine cause of the defects, light and scanning electron microscopy including EDS chemical microanalysis was used. Detailed study of the major defect and EDS microanalysis of its interior confirmed existence of defect prior to coating formation. Further examination of the major defect and its surroundings led to conclusion, that the defect was formed during primary foundry processes when billet was manufactured.