Skip to content

Sulfuric Anodize


What are AMS-A-8625 specs? 

When working with an industry as innovative and demanding as the Aerospace industry, there no room for error. To ensure compliance and quick turnaround times, many industries have established finishing specifications for their partners.  

ASM specs are process specifications that are set by the Society of Automotive Engineers (SAE).  ASM stands for Aerospace Material Specifications, and many of the jobs using this spec are in coordination with the aerospace industry.  

The SAE created ASM specs to help their contractors easily identify what specifications and proper practices need to be followed. At AOTCO, we pride ourselves on our dedication to these specs, as they allow us to continue to provide quality metal finishing for our partners in the aerospace industry. 

Why Use AMS-A-8625 Sulfuric Anodize? 

AMS-A-8625 is one of the most used specs for anodizing in the aerospace industry. The spec highlights 6 different types of anodizing as well as 2 different classes. Classes are used to determine whether the anodize is dyed. 

AMS-A-8625 also provides thickness requirements for each different type. These specifications make it easy for our team to quickly identify the type, class, and thickness requirements of the purchase order they are working on. 

AOTCO's Certifications & Approvals for this Spec

  • NADCAP Accredited
  • ROHS Compliant

Technical Notes

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


  • 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



























Alclad 2014-T6



Alclad 7075-T6












Thickness Ranges of Anodic Coatings on Aluminum and Aluminum Alloys

Coating Type

Thickness Range



1, 1B, 1C, and 2B

0.00002 to 0.00007



0.00007 to 0.0010



0.0005 to 0.0045


Coating Weight Relative to Type

Coating Type

Coating Weight (mg/ft2)

1 and 1B

200 min


200 min - 700 max


1000 min


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

Ready to get started?

Talk to an industry expert about the best solution for your application.


Join AOTCO at D2P Mohegan Sun | Southern New England

Spring has arrived to New England and that means it is time to get ready for fresh lobstah, the Boston Marathon, and fun at the Southern New England Design-2-Part Show....

AOTCO President Speaks At Harvard Business School Association

During a recent roundtable discussion at the Harvard Business School Association of Boston event, AOTCO's President, Matthew Smith, shared the remarkable journey of the...

Join AOTCO at MRO Americas 2024 | NADCAP Plating & Anodizing

Looking to secure your supply chain's NADCAP plating and anodizing services to drive innovation? Join AOTCO Metal Finishing at MRO Americas in Chicago!

Services & Capabilities

Plating Substrates
Pre- & Post-Process Treatments
Dedicated Outsourced Finishing



Electroplating is a process by which one metal is deposited onto a base metal (substrate). These deposited metals offer a variety of benefits including thermal and electrical conductivity, corrosion resistance and more. AOTCO electroplates a wide variety of both standard and exotic metals.

Learn More



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.

Learn More



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.

Learn More

Plating Substrates

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.

Learn More

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.

Learn More

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.

Learn More