Effects of the Heat Treatment on the Anodized Coating Properties of Al-Cu Alloys

Fine mechanical properties such as hardness and abrasion resistance are difficult to obtain for both the anodic oxide film and the base metal in sulfuric acid anodized coating. Age-hardening of Al-Cu alloys such as 2017 or 2024 are well known but we are not able to gain the fine properties of the anodic oxide film for these alloys. This report discusses the effect of heat treatment in subdividing and resolving soluble intermetallic compounds such as CuAl2, Mg2Si and Al2CuMg precipitated in a matrix of Al-Cu alloys to gain anodic oxide films with fine properties. By heating a matrix precipitating CuAl2, Mg2Si, Al2CuMg and other materials at optimum temperatures such as higher artificial aging temperatures but lower solution treatment before anodized coatings, these soluble intermetallic compounds are subdivided and resolved, and anodic oxide films are homogenuous and hard but the base metal is softened by heating so the next processes are given solid solution treatment and artificial aging. Through this processing, the strength of the base metal is recoverd in thermal refining such as T3 or T4 without the drop in hardness of films or the occurrence of cracks or peeling. Conclusions (1) The optimum temperature of heat treatment before anodized coating is about 400°C. (2) The abrasion and corrosion resistance of films are improved by this process. (3) Self-color anodized coatings such as gray or black are enable by this process.