NPFC - MIL-A-8625
ANODIC COATINGS FOR ALUMINUM AND ALUMINUM ALLOYS
|Publication Date:||10 September 1993|
This specification covers the requirements for six types and two classes of electrolytically formed anodic coatings on aluminum and aluminum alloys for non-architectural applications (see 6.1).
The anodic coating Types and Classes covered by this specification are as specified herein (see 6.2 and 6.21):
Type I - Chromic acid anodizing, conventional coatings produced from chromic acid bath (see 3.4.1) Type IB - Chromic acid anodizing, low voltage process, 22 ± 2V, (see 3.4.1) Type IC - Non-chromic acid anodizing, for use as a non-chromate alternative for Type I and IB coatings (see 3.4.1 and 6.1.2) Type II - Sulfuric acid anodizing, conventional coatings produced from sulfuric acid bath (see 3.4.2) Type IIB - Thin sulfuric acid anodizing, for use as a non-chromate alternative for Type I and IB coatings (see 3.4.2 and 6.1.2) Type III - Hard Anodic Coatings (see 3.4.3)
Class 1 - Non-dyed (see 3.5.) Class 2 - Dyed (see 3.6.)
Beneficial comments (recommendations, additions, deletions) and any pertinent data which may be of use in improving this document should be addressed to: Commanding Officer, Naval Air Warfare Center Aircraft Division Lakehurst, Code SR3, Lakehurst, NJ 08733-5100, by using the self-addressed Standardization Document Improvement Proposal (DD Form 1426) appearing at the end of this document or by letter.
The coatings covered in this document are intended to yipvide corrosion resistance, improved paint adhesion and abrasion resistance as specified in 6.1.1 through 6.1.3. This document is not... View More
The coatings covered in this document are intended to yipvide corrosion resistance, improved paint adhesion and abrasion resistance as specified in 6.1.1 through 6.1.3. This document is not intended to sufficiently cover anodic coatings for use in structural adhesive bonding.
The conventional Types I, IB and II anodic coatings are intended to improve surface corrosion protection under severe service conditions or as a base for paint systems. Anodic coatings can be colored with a large variety of dyes and pigments. Types I, IB and II coatings provide better corrosion protection at higher cost than the chemical conversion systems. Repair of mechanically damaged areas by the use of materials conforming to MIL-C-81706 (see 3.3.4) will not restore abrasion resistance but will provide an effective means of reestablishing corrosion resistance. Where anodic coatings are required on fatigue critical components, Type I and IB coatings (see 6.1.2) are used due to the thinness of the coating (see 6.10.7).
Type IC and IIB coatings provide non-chromate alternatives to Type I and IB coatings where corrosion resistance, paint adhesion, and fatigue resistance is required. Please note that Type IC or IIB may not serve as suitable replacements when the effects of electrolyte entrapment is the primary concern (see 184.108.40.206 and 220.127.116.11). Maximum Type IC and Type IIB coating weights of 700 mg/ft2 and 1000 mg/ft2, respectively, are specified in Table I for fatigue purposes (see 6.10.7). If higher Type IC coating weights are permissible for the intended use, it should be specified in the contract or purchase order (see 6.2). If higher Type IIB coating weights are permissible for the intended use, Type II should be specified.
Type III coatings are intended to provide wear and abrasion resistant surfaces with improved corrosion protection due to greater thickness and weight than the conventional anodic coatings. Sealing of Type III coatings is not recommended unless corrosion resistance is also a factor. Wear resistance is reduced by sealing. Anodic coatings form an excellent base for most types of paint systems, adhesives and dry film lubricants. Hard coatings may reduce fatigue strength. These factors should be considered in proposed use of parts subjected to cyclic loads. Generally, these hard coatings should not be used on parts or portions of parts which normally during rework would require restoring of dimensional tolerances because of wear of hard coated surfaces.
Type III coatings are used in such applications as valves, sliding parts, hinge mechanisms, cams, gears, swivel joints, pistons, rocket nozzles, insulation plates, blast shields, etc.View Less