Abnormal Color Analysis of Anodized Oxidation Film of a 2D70 Aluminum Alloy Cylindrical Part

Aiming at the abnormal white color defect of anodized oxidation film on the surface of a 2D70 aluminum alloy cylinderical part, the microstructure,micro-area composition, precipitation and the conductivity of the matrix and the oxidation film were studied by the optical microscope, scanning electron microscope, transmission electron microscope and conductivity meter and the reason for the abnormal white color was analyzed. The results show that the precipitations in some areas of the cylindrical part grew abnormally due to the high temperature during the ageing process. These coarse precipitations resulted in the current density fluctuation in these areas during the anodized oxidation process, leading to the different relative density of the film from that of the surrounding normal areas. The different relative density caused the different ability of the reflecting power, leading to the abnormal white color. Some measures such as hanging the parts during the ageing treatment can be adopted to avoid the partially high temperature.