Anodized aluminum with dark gray color

Abstract

Provided herein are aluminum alloys and aluminum sheets including alloys that have a natural dark gray color when anodized. The alloys do not require any absorptive or electrolytic coloration process separate from the anodization process to achieve the dark gray coloration. Also provided herein are methods for making such aluminum alloys.

What is claimed is: 
     
         1 . An aluminum alloy comprising about up to 0.40 wt. % Fe, up to 0.25 wt. % Si, up to 0.2 wt. % Cr, 2.0 wt. % to 3.2 wt. % Mg, 0.8 wt. % to 1.5 wt. % Mn, up to 0.1 wt. % Cu, up to 0.05 wt. % Zn, up to 0.05 wt. % Ti, and up to 0.15 wt. % impurities, with the remainder as Al. 
     
     
         2 . The aluminum alloy of  claim 1 , wherein the aluminum alloy comprises 0.05 wt. % to 0.2 wt. % Fe, 0.03 wt. % to 0.1 wt. % Si, up to 0.05 wt. % Cr, 2.5 wt. % to 3.2 wt. % Mg, 0.8 wt. % to 1.3 wt. % Mn, up to 0.05 wt. % Cu, up to 0.05 wt. % Zn, up to 0.05 wt. % Ti, and up to 0.15 wt. % impurities, with the remainder as Al. 
     
     
         3 . The aluminum alloy of  claim 1 , comprising at least 1.5 weight percent Al 6 Mn and/or Al 12 (Fe,Mn) 3 Si. 
     
     
         4 . An aluminum sheet comprising the aluminum alloy of  claim 1 . 
     
     
         5 . The aluminum sheet of  claim 4 , wherein the aluminum alloy sheet comprises an oxide surface layer. 
     
     
         6 . The aluminum sheet of  claim 4 , wherein the aluminum alloy sheet has a white balance of lower than 35 as measured by ASTM E313-15 (2015). 
     
     
         7 . The aluminum sheet of  claim 4 , further comprising dispersoids at a density of at least 2 disperoids per 25 square micrometer. 
     
     
         8 . The aluminum sheet of  claim 7 , wherein the dispersoids have an average dimension of greater than 50 nanometers in any direction. 
     
     
         9 . The aluminum sheet of  claim 8 , wherein the dispersoids comprise one or more of Al 3 Fe, Al x (Fe,Mn), Al 3 Fe, Al 12 (Fe,Mn) 3 Si, Al 7 Cu 2 Fe, Al 20 Cu 2 Mn 3 , Al 3 Ti, Al 2 Cu, Al(Fe,Mn) 2 Si 3 , Al 3 Zr, Al 7 Cr, Al x (Mn,Fe), Al 12 (Mn,Fe) 3 Si, Al 3 ,Ni, Mg 2 Si, MgZn 3 , Mg 2 Al 3 , Al 32 Zn 49 , Al 2 CuMg, and Al 6 Mn. 
     
     
         10 . The aluminum sheet of  claim 8 , wherein the dispersoids comprise Al—Mn—Fe—Si. 
     
     
         11 . The aluminum sheet of  claim 8 , wherein the dispersoids comprise one or more of Al 3 Fe, Al 12 (Fe,Mn) 3 Si, Al 20 Cu 2 Mn 3 , Al(Fe,Mn) 2 Si 3 , Al 3 Zr, Al 7 Cr, Al 12 (Mn,Fe) 3 Si, Mg 2 Si, and Al 2 CuMg, and Al 6 Mn. 
     
     
         12 . The aluminum sheet of  claim 4 , comprising a grain size of from 10 microns to 50 microns. 
     
     
         13 . A method of preparing an aluminum sheet comprising dispersoids, the method comprising:
 casting an aluminum alloy to form an ingot;   homogenizing the ingot to form a homogenized ingot;   hot rolling the homogenized ingot to produce a hot rolled intermediate product;   cold rolling the hot rolled intermediate product to produce a cold rolled intermediate product;   interannealing the cold rolled intermediate product to produce an interannealed product;   cold rolling the interannealed product to produce a cold rolled sheet; and   annealing the cold rolled sheet to form an aluminum sheet comprising dispersoids,   wherein the aluminum alloy comprises a 2xxx, 3xxx, 5xxx, or 7xxx series alloy.   
     
     
         14 . The method of  claim 13 , further comprising anodizing the aluminum sheet. 
     
     
         15 . The method of  claim 13 , wherein the aluminum alloy comprises about up to 0.40 wt. % Fe, up to 0.25 wt. % Si, up to 0.2 wt. % Cr, 2.0 wt. % to 3.2 wt. % Mg, 0.8 wt. % to 1.5 wt. % Mn, up to 0.1 wt. % Cu, up to 0.05 wt. % Zn, up to 0.05 wt. % Ti, and up to 0.15 wt. % impurities, with the remainder as Al. 
     
     
         16 . The method of  claim 13 , wherein the dispersoids comprise one or more of Al 3 Fe, Al x (Fe,Mn), Al 3 Fe, Al 12 (Fe,Mn) 3 Si, Al 7 Cu 2 Fe, Al 20 Cu 2 Mn 3 , Al 3 Ti, Al 2 Cu, Al(Fe,Mn) 2 Si 3 , Al 3 Zr, Al 7 Cr, Al x (Mn,Fe), Al 12 (Mn,Fe) 3 Si, Al 3 ,Ni, Mg 2 Si, MgZn 3 , Mg 2 Al 3 , Al 32 Zn 49 , Al 2 CuMg, and Al 6 Mn. 
     
     
         17 . The method of  claim 13 , wherein the aluminum sheet has a white balance of lower than 35 as measured by ASTM E313-15 (2015). 
     
     
         18 . The method of  claim 13 , wherein the dispersoids are present in the aluminum sheet at a density of at least 2 disperoids per 25 square micrometers.