Abstract
Al-Mn-Cr alloys were anodized in a sulfuric acid solution and color of anodized films was measured quantitatively. Dependence of the color on alloy compositions and heat treatment was studied and a coloring mechanism was discussed in terms of quantum chemistry. Following results were obtained:
(1) When super saturated solid solutions were anodized, films on high manganese alloys showed light pink color while films on high chromium alloys developed yellow color. When contents of manganese and chromium were intermediate, light pink and yellow hues overlapped and the film color turned to be brown because the stimulus value, Y, lowered.
(2) When alloys had been precipitation annealed prior to anodizing, high chromium alloys developed slight coloring. However, the color was grey because of the extremely low stimulus value.
(3) Coloring by manganese and chromium was due to Mn3+ and Cr6+, respectively. Formation of films with slightly greenish color on annealed alloys was possibly due to Cr3+ contribution.
(4) Dispersed precipitates in films resulted in blackening by scattering. Scattering by smaller precipitates produced bluish color.
(5) It appeared that the coloring mechanism active in the present study was similar to that of colored glass, laser materials or certain jewels.
