MIL SPEC GUIDE

Chemical Films (MIL-C-5541F)

Electroless Nickel

(MIL-C-2404D)

Hard Anodize

(MIL-A-8625F)

Nickel

(QQ-N-290A)

Passivate

(QQ-P-35C)

Sulfuric Anodize

(MIL-A-8625F)

Tin 

(MIL-T-10727B)

Zinc

(ASTM-B633)

Chemical Films (MIL-C-5541F)

Materials qualified produce coatings that range in color from clear to iridescent yellow or brown. Inspection difficulties may arise with clear coatings because visual inspection does not reveal the presence of a coating.

Class 1A For maximum protection from corrosion, for surfaces to be painted or left unpainted.

Class 1A chemical conversion coatings are intended to provide corrosion prevention when left unpainted and to improve adhesion of paint finish systems to aluminum and aluminum alloys may be used for all surface treatments of tanks, tubing's and component structures where interior paint finishes are not required. Repair of mechanically damaged areas of anodic coatings conforming to MIL-A-8625 will provide effective means of reestablishing corrosion resistance but will not restore abrasion resistance of the anodic coating.

Class 3 Class 3 chemical coatings are intended as a corrosion preventive film from electrical and electronic applications where low resistance contacts are required.

Electroless Nickel (MIL-C-2404D)

Similar to stainless steel in color. Plates uniformly in recesses and cavities (does not build up on edges). Corrosion resistance is good for coatings over .001 thickness. Electroless Nickel is used extensively in salvage of miss-machined parts. Also for inside dimensions and irregular shapes (where assembly tolerances need uniformity provided by Electroless process).

Class 2 Baking Schedule to Achieve Hardness

Temp. (degrees F)          Hours
               450                   16
              500                    2
              550                    1
                600                   0.5

Achieve Hardness on nickel, copper, cobalt and titanium base alloys by baking 650 +/- 10 degrees F for 1-1 1/2 hours

(Unless otherwise specified)

Class 1           As coated.

Class 2           Steel, copper, nickel, cobalt-titanium based alloys

                        and any basis metal not adversely affected by

                        heating as specified.

Class 3           Aluminum alloys non-heat-treatable, and

                        beryllium alloys processed to improve adhesion

                        of nickel deposit.

Class 4           Aluminum alloy, heat-treatable, processed to

                        improve adhesion of the nickel deposit.

Grade A         .001” Min. thickness

Grade B         .0005” Min. thickness

Grade C         .0015” Min. thickness (for severe corrosion

                         protection).

Hard Anodize (MIL-A-8625F)

Color will vary from light tan to black depending on alloy and thickness. Can be dyed in darker colors depending on thickness. Coating penetrates base metal as much as builds up on the surface. Provides very hard ceramic type coating. Good dielectric properties.

Corrosion resistance is good, but recommended seal hard anodize in 5% dichromate solution where increased corrosion resistance is required. Where extreme abrasion resistance is required do not seal as some softening is encountered.

(As specified on drawing. if not specified normal thickness shall be 0.002”)

Type III:     Most aluminum alloys depending on process used. Where maximum serviceability or special properties are required, consult metal finisher for best alloy choice. Thick coatings (over .004”) will tend to break down sharp edges. Typical applications: hydraulic cylinders, wear surfaces, actuating cams, etc... Can be used as an electrical insulation coating.  “Flash” hard anodize may be used instead of conventional anodize for corrosion resistance and may be more economical in conjunction with other hard anodized areas.

Class 1:   Non-dyed               

Class 2:   Dyed

Nickel (QQ-N-290A)

There is a nickel finish for almost any need. Nickel can be deposited soft or hard-dull or bright, depending on process used and conditions employed in plating. Thus, hardness can range from 150-500 Vickers. Can be similar to stainless steel in color, or can be dull gray or light gray (almost white) color. Corrosion resistance is a function of thickness. Has a low coefficient of thermal expansion-is magnetic. All steel parts having a hardness of Rc-40 or greater require a post bake @375 degrees +/- 25 degrees for 3 hours.

Class 1A:          For corrosion protection

Grade A:           .0016” 

Grade B:           .0012”

Grade C:           .0010”

Grade D:           .0008”

Grade E:           .0006”

Grade F:           .0004”

Grade G:           .0002”

Class 2:            For engineering applications

Passivate (QQ-P-35C)

Specification covers standard recommendation practice for cleaning and de-scaling stainless steel parts, equipment and systems. Cleaning includes all operations necessary for the removal of surface contaminants from metals to ensure: 

(1)    maximum corrosion resistance for the metal. 

(2)    prevention of product contamination; and 

(3)    achievement of desired appearance. (has no dimensional

         change) 

Type I:      Low temperature 

Type II:     Medium temperature 

Type III:    High temperature 

Type IV:   For steels containing large amounts (0.15%) of sulfur

                   or selenium. 

Type V:    Anodic-for high carbon martensitic (440 steels).

Type VI:   Low temperature (optional).

Sulfuric Anodize (MIL-A-8625F)

Color will vary with alloy. Aluminum with low alloying elements will show practically no color change. Best coating on aluminum for dyeing. Can be dyed practically any color or shade. Minimum weight Type II coatings. Class 1 - 600 milligrams/sq. ft. Class 2 - 2500 milligrams/sq. ft. NOTE: For wrought 2000 series and castings with 1% or greater copper min. coating wt. shall be 14000 milligrams/sq. ft. Type II: .00005”-.0010” All aluminum alloys, but do not use where solution will entrap.

                            Class 1:    Non-dyed                    

Class 2:    Dyed

Tin (MIL-T-10727B)

Color is gray white in plated condition. Had very high luster in fused condition. Soft, but is very ductile. Corrosion resistance is good. (Coated items should meet 24 hour 5% salt spray requirement.) Solder ability is excellent. Tin is not good for low temperature applications (changes structure and loses adhesion when exposed to temperatures below -40 degrees C). If a bright finish is desired to be used in lieu of fused tin, specify Bright Tin plate. Thickness can exceed that of fused tin and in deposit shows excellent corrosion resistance and solder ability. 

Type I:   Electrodeposited 

Type II:  Hot dipped 

           .0001 - .00025”: Flash for soldering  

           .0002 - .0004”:   to prevent galling and seizing 

           .0003” min:        Where corrosion resistance is important.

           .0002 - .0006”:   To prevent formation of case during

                                        nit-riding.

Zinc (ASTM-B633)

This specification covers requirements for electrodeposited zinc coatings applied to iron or steel articles to protect them from corrosion.  It does not cover zinc coated wire or sheets.  High strength steels (tensile strength greater than 1700 M.p.a.) shall not be electroplated.  Stress relief:  All parts with ultimate tensile strength 1000 M.p.a. and above at min. 190 degrees C for 3 hours or more before cleaning and plating.  Hydrogen embrittlement relief:  All electroplated parts 1200 M.p.a. or higher shall be baked at 190 degrees C for 3 hours or more within 4 hours after electro-plating.

Type I:     As plated;     

Type II:    With colored chromate conversion coatings;

Type III:   With colorless chromate  conversion coatings;  

Type IV:   With phosphate conversion coatings.

Thickness Classes for Coatings:

Fe/Zn 25 = SC 4 (very severe)    

Fe/Zn 13 = SC 3 (severe)   

Fe/Zn 8 = SC 2 (moderate)    

Fe/Zn 5 = SC 1 (mild)