MIL-P-81985 "Peening of Metals" states in section 3.5.2.1 "Aluminum parts. Unassembled aluminum and aluminum alloy parts without inserts may be cleaned by immersion in a nitric acid solution for 20 to 40 minutes at 120° to 140°F (49° to 60°C). The solution shall consist of the following:
nitric acid( (Sp. gr. 1.42) 200 to 500ml.
Water to make 1.1
Nitric acid base deoxidizer solutions used prior to the application of anodic and chemical conversion coatings may be used provided they meet the acid strength requirements (see 6.14)
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