Lately, the colored anodizing aluminium alloys have often been used as the building materials. As a study on the brown anodizable Al-Cr-Mn alloys, the present experiments were carried out to investigate the relation among the color of oxide film after anodizing in sulfuric acid solution, the contents of Cr and Mn added to Al alloys of various purities and the heat treatment.
The results obtained are as follows:
Al-Cr-Mn alloys containing of Cr≥0.2∼0.3% and Mn≥0.2∼0.3% show brown or bronze color after the anodizing treatment in the single phase state. In this case the brown color became clearer with the Cr and Mn contents, but the alloys present black color when large amounts of the intermetallic compounds of Al-Cr-Mn precipitated from the super saturated solid solution of the alloys. This might be attributed to the light of incidence which are absorbed or scattered by these compounds retained in the oxide film after anodizing.
Al-Cr-Mn alloys produced by the aluminium of lower purity show a dull brown color after anodizing, because the impurities facilitate the precipitation of Cr and Mn and also cause the scattering of the light of incidence.