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Hard Anodizing per MIL-A-8625 with chromic acid

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Does Type III Class 2 "Hard" Anodizing per Mil-A-8625 [link is to spec at TechStreet] have to be sulfuric, or can it also be Chromate (it shall not be sealed)?

Stacie Temple
Contract Manufacturing - Hunstville, Alabama

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Hard Coat may be sulfuric, oxalic, or a combination, but you cannot get hard coat thickness with Chromic Acid Anodizing.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

Editor's note:
   Mr. Probert is the
   author of

Aluminum How-To / Aluminio El Como

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To add to what Robert said, Class 2 denotes a dying process, and to my knowledge, one cant dye chromic acid anodizing, nor oxalic acid anodizing (oxalic acid anodizing may be able to be dyed, but in 17 years of experience, I've never come across it). I'd go with the sulfuric.

Marc Green
anodizer - Boise, Idaho

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