Surface Finishing Tutorial

#088 Natural Colorization of Anodizing

Category : Anodizing

July22, 2011

The color of anodize coatings vary depending on the electrolytic process conditions such as aluminum alloy type, electrolyte bath, and power supply waveform. The [Table 1] and [Table 2] show electrolytic colorization under a DC power supply, and these colors will vary further by the coating thickness. Thicker coatings will have darker colors.

[Table 1] Natural Colorization of Anodize Coatings (Rolled material)

Alloy Group	Representative Alloys	Color Tone of Anodize Coating
Alloy Group	Representative Alloys	Hydrochloric Acid Bath	Oxalic Acid Bath
Pure AL Group	1050, 1100	Silver White Color	Gold - Yellow Tan
AL - Cu Group	2017, 2024	Gray White	Light tan - Gray Red
AL - Mn Group	3003, 3004	Silver White - Light Yellow	Yellow Tan
AL - Si Group	4043	Gray - Gray Black	Gray Yellow - Gray Yellow Black
AL - Mg Group	5005, 5052	Silver White - Light Yellow	Gold
AL - Mg - Si Group	6061, 6063	Silver White - Light Yellow	Gold
AL - Zn - Mg Group	7072	Silver White	Gold

[Table 2] Natural Colorization of Anodize Coatings (Cast / Die-cast)

Alloy Type		Contained Components	Color Tone of Anodize Coating
Alloy Type		Contained Components	Hydrochloric Acid Bath	Oxalic Acid Bath	Chromic Acid Bath
Cast	AC1A, 1B, 5A	High Cu with low Si	Light Red	Light Red Tan	Red Gray
	AC2A, 2B, 3A4A, 4B, 4C, 4D, 8A, 8B, 8C	With Si 5% or more	Gray -> Dark Gray	Gray -> Dark Gray	Gray -> Dark Gray
	AC7A	High Mg with low Si	White Silver	Tan	Gray White
Die - cast	ADC1, 3, 10, 12, 14	High Si content	Gray -> Black	Black Tan	Gray Black
Die - cast	ADC5, 6	High Mg with low Si	Clear -> White Silver	Gold	Gray White

Therefore, the following must be considered when designing products with anodizing.

1. When selecting an aluminum alloy material, confirm that a desired color can be obtained by anodizing process.

2. When useable aluminum alloy is limited due to manufacturing method and strength for usage, and such alloy has its distinctive anodized color, use dying or electrolytic coloring to obtain the desired color.

3. When dark colorization is unavoidable due to specific condition such as applying a hard anodizing on some specific alloys, have the clients understand that the colors cannot be changed in order to preserve the wear resistant property of the coating.

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