MIL-DTL-83488D
3.1.1 Composition. The composition of the aluminum coating shall not be less than 99.0
percent aluminum.
3.2
Equipment and processes. As specified in 3.9.2, the equipment and processes employed
to produce high purity aluminum coatings shall be capable of providing a uniform coating.
3.2.1 Processes. The process used to deposit the coating shall not cause a temperature rise in
the parts that could cause adverse reaction between the coating and the substrate or adversely
affect the substrate.
3.2.1.1 Cleaning. All base metals shall be cleaned in accordance with MIL-S-5002 or equivalent
cleaning method, prior to coating with high purity aluminum.
3.3
Areas of deposit. Except as specified in 3.5.4, the coating shall completely cover all
visible surfaces, including roots of threads, and sharp corners. The coating shall be deposited
directly on the base metal without a preliminary coating of other metal.
3.4
Supplementary chromate treatment (Type II). Unless otherwise specified, the high
purity coating shall be Type II, which is a Type I coating with a supplementary chromate
treatment in accordance with MIL-C-5541, Class 1A. Chromate treated parts, other than
fasteners, should receive additional protective coatings. Application requiring electrical
conductivity (see 6.1) shall be chromate treated with a MIL-C-5541 solution which meets both
Class 1A (corrosion resistance) and Class 3 (low electrical resistance) requirements.
3.5
Thickness of coating. Except as specified in 3.5.4, the thickness of high purity
aluminum shall be as specified in 1.2.1 on all visible surfaces.
3.5.1
Class 1 thickness. Class 1 thickness shall be used where tolerance will permit.
3.5.2 Class 2 thickness. Class 2 thickness shall be used where Class 1 thickness is
unacceptable for dimensional thickness reasons.
3.5.3 Class 3 thickness. Class 3 thickness shall be used for close tolerance applications such as
finely threaded parts.
3.5.4 Exceptions to Class 1, 2, and Class 3 thickness. Fixture contact points, holes, recesses,
internal threads, and other areas where a controlled deposit cannot be obtained shall not be
subject to a thickness requirement. However, there shall be visual evidence of coating in holes
and recesses down to a depth of at least the diameter of the hole or recess. Fastener areas that
cannot be touched with a 0.020-inch diameter ball shall not be subject to thickness requirement.
Threads that gage undersize solely as a result of coating thickness shall be considered acceptable.
3.6
Stripping of aluminum coatings. Steel parts to be recoated shall be stripped by
mechanical means or in a suitable caustic solution. If stripped with caustic solution, steel parts
having hardness Rockwell C-40 or greater shall be baked after stripping at an appropriate time
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