PLATING
FINISHES FOR CORROSIVE ENVIRONMENTS

Coating or Finish For Use On Degree of Corrosion Resistance Characteristics
Anodizing Aluminum Excellent Acid electrolytic treatment for aluminum , frosty-etched appearance. Hard oxide surface gives excellent protection.
Black chromate Zinc-plated or cadmium plated steel Added corrosion protection on cadmium and zinc-plated surfaces Black , semilustrous. Chemical dip. Used for decorative outdoor purposes. Can be lacquered.
Cadmium plate Most metals Excellent Bright silver-gray , dull gray , or black electroplated finish. For decoration and corrosion protection (especially marine applications).
Clear chromate finish Cadmium and zinc-plated parts Very good to excellent Clear bright or iridescent shemical conversion coating applied to zinc or cadmium-plated surfaces for added corrosion protection , coloring , and paint bonding. The colored coatings usually have greater corrosion resistance than the clear.
Dichromate Cadmium and zinc-plated parts Very good to excellent Yellow , brown , green , or Iridescent colored coating same as clear chromate.
Olive drab , gold or bronze chromate Cadmium and zinc-plated parts Very good to excellent Green , gold , or bronze tones same as clear chromate.
Chromium plate Most metals Good(Improves with increased copper and nickel undercoats) Bright blue-white , lustrous electroplated finish. Has relatively hard surface. Used for decorative purposes.
Copper plate Most metals Fair electroplated finish. Used for nickel and chromium-plate undercoat. Can be blackened and relived to obtain Antique , Statuary , and Venetian finishes.
Copper , brass , bronze , misc. finishes Most metals Indoor , very good Decorative finishes. Applied to copper , brass , bronze-plated parts to match colors.Color and tones vary from black to almost the original color.Finish names are Antique , Black Oxide , Statuary, Old English , Venetian , Copper Oxidized.
Bright nickel Most metals Indoor excellent , Outdoor good if thickness is at least 0.0005 in. Electroplated silver finish. Used for appliances , hardware , etc.
Dull nickel Most metals Same as bright nickel Whitish cast. Can be obtained by mechanical surface finishing or using a special plating bath.
Passivating Stainless steel Excellent Chemical treatment. Removes iron particles and produces as passive surface.
Zinc or Manganese Phosphate Steel Very good Antichafing properties on sliding or bearing surfaces. Black manganese-iron phosphate coating with nondrying petroleum oils containing corrosion inhibitors.
Colored phosphate coatings Steel Superior to regular phosphated and oiled surfaces. Chemically produced color coating will increase corrosion resistance. Avaliable in green , red , purple , blue , black , etc.
Rust preventatives All metals Varies with function of oil Vary in color , and film thickness. Usually applied to phosphate and black oxide finishes. Used to protect parts in transit or prolonged storage.
Silver plate All metals Excellent Decorative , expensive. Excellent electrical conductor.
Electroplated tin All metals Excellent Silver-gray color. Excellent corrosion protection for parts in contact with food.
Electroplated zinc All metals Very good Bright-blue-white gray coating. For corrosion protection of steel parts.


PLATING & COATING SPECIFICATIONS

Type Thickness Class Pre or post-plate treatments or instructions Federal Specifications
1 2 3
cadmium

Must be specified

 clear post plate drip AMS 2400
cadmium .0005 min .0003 min .0002 min none QQ-P-416 Type I
cadmium .0005 min .0003 min .0002 min iridescent dichromate QQ-P-416 Type II
zinc .0010 min .0005 min .0002 min none QQ-Z-325 Type I
zinc .0010 min .0005 min .0002 min iridescent dichromate QQ-Z-325 Type II
zinc .0010 min .0005 min .0002 min supplementary phosphate QQ-Z-325 Type III
zinc FE/ZN 12 .0005 min FE/ZN 8 .0003 min FE/ZN 5 .0002 min none ASTM B633 Type I
zinc FE/ZN 12 .0005 min FE/ZN 8 .0003 min FE/ZN 5 .0002 min iridescent dichromate ASTM B633 Type I
silver Must be Specified nickel strike AMS 2410
AMS 2411
silver Must be Specified copper strike AMS 2412
dull nickel Must be Specified   QQN 290 Class 2
dull chrome Must be Specified   QQC 320 Class 2
phosphate Type M .0002-.0004 .0002-.0004 .0002-.0004 drying oil
non-drying oil
dry		 DOD-P-16232
phosphate Type Z .0002-.0004 .0002-.0004 .0002-.0004 drying oil
non-drying oil
dry		 DOD-P-16232
black oxide    MIL-C-13924
IVD aluminum .0010 min .0005 min .0003 min chromate MIL-C-83488 Type II

FORMULA for THREAD SIZE BEFORE PLATING
In computing thread pitch diameter before plating, it has been general practice to follow the rule that the pitch diameter size of an external screw thread is theoreticall increased 4 times the plating thickness.  However, variables in thickness of coating, symmetry of coatings resulting from commercial processes, and extreme lengths have necessitated a revision of the theoretical allowance.  The following formulas are offered as general references for Class 2A and 3A thread fits before plating.

Screw
Diameter		 PITCH DIAMETER REDUCTION
Maximum Minimum
No. 0-3 4x Max. Plating Thickness 3x Max. Plating Thickness
No. 4-12 5x Max. Plating Thickness 4x Max. Plating Thickness
1/4 - 1/2 5x Max. Plating Thickness 4x Max. Plating Thickness
9/16 & up 6x Max. Plating Thickness 4x Max. Plating Thickness


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