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MIL-PRF-8625 *
Sulfuric Anodize

Plating Specs

What Are Mil-PRF-8625 Specs? 

Mil-PRF-8625 is the latest version of the Mil-A-8625 spec. Unchanged since 2003, Mil-A-8625 was updated in 2020 to provide clarity for auditors and industry members. Mil-PRF-8625 was created, with PRF indicating that the specification is for performance.  

AOTCO’s work with the defense and military industries continues to be some of our most detail oriented. Our team is well versed in military plating requirements and complies with the latest mil-specs and processes. Our team of platers and engineers are proud to deliver the highest quality surface finishing processes.  

* Note: MIL-A-8625 is an older version of this spec. Owing to ongoing customer demand AOTCO continues to finish to this spec as well as the current MIL-PRF-8625 spec.

AOTCO's Certifications & Approvals for Mil-PRF-8625

  • NADCAP Accredited
  • ROHS Compliant

Plating Specs for MIL-PRF-8625 Hard Anodize

PRF-8625 Types of Anodic Coatings Available

  • Type 1 – Conventional coatings produced from chromic acid bath
    Purpose: Delivers an electrically non-conductive surface with improved scratch and corrosion resistance. Primarily used in aerospace applications and on castings where components that may undergo flexing due to heat changes or mechanical means

  • Type 2 – Sulfuric acid anodizing, conventional coatings produced from sulfuric acid bath
    Purpose: Intended to improve surface corrosion protection under severe service conditions or as a base for paint systems
  • Type 2B – Thin sulfuric acid anodizing, for use as non-chromate alternative for Type 1 and 1B coatings
    Purpose: Non-chromate alternative to Type 1 and 1B coatings, where corrosion resistance, paint adhesion, and fatigue resistance are all required

  • Type 3 – Hard Anodic Coatings
    Purpose: Provide wear and abrasion resistant surfaces with improved corrosion protection due to greater thickness and weight than the conventional anodic coatings. Reminder: Sealing of Type 3 coatings is not recommended unless corrosion resistance is also a factor, as both wear resistance and fatigue strength can be reduced by sealing

Types of Anodic Coatings NOT Offered

  • Type 1B – Chromic acid anodizing, low voltage process

  • Type 1C – Non-chromic acid anodizing, for use as non-chromate alternative for Type 1 and 1B coating

Classes

  • Class 1 – Non-dyed
  • Class 2 – Dyed

Acquisition Requirements

Acquisition documents should specify the following

  • Assembly Anodizing – If an assembly is required, customer MUST provide AOTCO with this information.

  • Due to electrolyte entrapment, assembly anodize must be pre-approved by AOTCO on a PART TO PART basis

  • Type of anodic coating, title, number and date of this specification

  • Class of anodic coating

  • Special process operating conditions, if applicable

  • Special cleaning and fabrication requirements

  • Color and uniformity of Class 2 coatings, if applicable

  • Degree of non-uniformity of dyed casting alloys

  • Type 3 coating thickness, if applicable

  • Coating weight for thickness, (for Type 3) if substituted

  • Special sealing requirements

  • When applicable, the allowable difference in anodic coating appearance resulting from inherent base metal differences

  • Provide the specific location of contact marks if important to the function of the part

  • Acceptance criteria for quality conformance inspections

  • If paint adhesion testing is required for quality conformance testing and the required paint system

Unless otherwise specified in the contract, PO, or applicable drawing, the nominal thickness of the coating shall be 0.002 inches (2 mils).

Minimum Thickness (typical) in inch of Anodic Coatings

Alloy Designation

Type 2 Thickness of Coating

Inches

Mils

1100

0.000093

0.093

2024-T4

0.000125

0.125

2024-T6

-

-

3003

0.000103

0.103

5052

0.000098

0.098

5056

-

-

6061-T6

0.000099

0.099

7075-T6

-

-

Alclad 2014-T6

-

-

Alclad 7075-T6

-

-

295-T6

0.000107

0.107

356-T6

0.000102

0.102

514

0.000086

0.086

Thickness Ranges of Anodic Coatings on Aluminum and Aluminum Alloys

Coating Type

Thickness Range

Inches

Mils

1, 1B, 1C, and 2B

0.00002 to 0.00007

.02-.07

2

0.00007 to 0.0010

.07-0.1

3

0.0005 to 0.0045

0.5-4.5

Coating Weight Relative to Type

Coating Type

Coating Weight (mg/ft2)

1 and 1B

200 min

1C

200 min - 700 max

2

1000 min

2B

200 min - 1000 max

Additional Relationships to Consider When Designing Part Coating
  • Fatigues properties of aluminum alloys can be severely reduced by anodic coatings. The amount of reduction varies with the process. As a rule of thumb, the thicker the coating the greater the fatigue will be
  • Hardcoat of 2 mils or more is extremely difficult to obtain on high silicon dye castings such as 360, 380, and 383
  • Abrasion resistance in Type 3 hardcoat will decrease as the thickness of coating approaches 3 mils. In general, abrasion resistance does NOT increase with coating thickness

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Resources

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Services & Capabilities

Electroplating
Anodizing
Passivation
Plating Substrates
Pre- & Post-Process Treatments
Dedicated Outsourced Finishing
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Electroplating

Electroplating

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Anodizing

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Sometimes called a “conversion coating” Anodizing is an electrolytic process in which an oxide (anodic) layer is chemically built on the surface of the substrate material, providing anti-corrosion and other benefits. AOTCO offers, Type I, Type 2, Type 3 and Titanium anodizing services.

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Passivation

Passivation is a term for a variety if processes that make a metal (most commonly stainless steel) or other substance unreactive, or passive, by altering the surface layer or coating the surface with a thin inert layer. AOTCO performs both citric and black oxide passivation techniques to a range of specifications.

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Plating Substrates

AOTCO plates on a wide variety of Common, Exotic and Non-Metallic substrates, bringing exceptional expertise to magnesium, titanium, beryllium, BeCu, TeCu, tungsten and more. In some cases we pass as high as 450 degrees celsius, allowing for high temperature soldering, brazing, or post machining operations after plating.

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Pre- & Post-Process Treatments

Pre- & Post-Process Treatments

Pre-Process: In addition to offering both mechanical & chemical cleaning options, AOTCO specializes in creating solutions for complicated, difficult and tight-tolerance masking challenges. Post-Process: For clients with specialized needs AOTCO offers laser marking and engraving options, including color change caused by chemical or molecular changes, charring, foaming, melting, ablation, and more.

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Dedicated Outsourced Finishing

Dedicated Outsourced Finishing

Part of our cornerstone goal of building long-term, collaborative & solution-oriented partnerships, AOTCO will devote reserved physical and human resource capacity for our clients with long-term finishing and deadline requirements. For these partnerships our commitment is that AOTCO manages the process, while YOU control the results.

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