Metal finishing is done to make traditional parts more effective for a variety of different use cases. Anodizing requires high-performance machinery and expertise to be executed properly.
The anodizing process is a critical treatment of metal to enhance aluminum without adding an additional layer to the surface. Instead, the process of anodic oxidation builds up through a molecular compound bond directly integrated with the aluminum surface.
Anodizing adds protection to your aluminum surface for more corrosion resistance, a longer-lasting appearance, and improved wear resistance properties. At DiFruscia Industries, Inc., we have the necessary expertise to provide high-quality anodizing finishes for a wide range of industries.
What Is Anodizing?
Anodizing is when a metal surface is coated with an electrically conducting, water-repellent, and corrosion-resistant layer. This layer becomes more attractive and durable with an anodic oxide finish.
The most commonly anodized metal is an aluminum surface because the oxide becomes completely assimilated into the metal rather than only adding an additional layer onto the surface. This makes the finish more permanent with stronger properties compared to an anodized finish on metals like steel or iron.
This electrochemical process adds thickness and toughness to the surface of aluminum because of the oxide present in the solution. These protective coatings are designed to be extremely tough and resistant to external forces like corrosion.
Anodized coatings can vary in color, size, and thickness. Typical coatings range between 0.1 to 1.0 mils in thickness with a relatively transparent aesthetic look. The most important aspect of anodizing is that it allows your aluminum parts to maintain their natural texture and metal integrity.
In this guide, we will discuss the three primary types of anodizing: Type I, Type II, and Type II.
How Does The Anodizing Process Work
Despite the large number of chemicals and equipment involved, the anodizing process is not as intimidating as it might seem. It requires five thorough steps to properly execute a high-quality anodized finish. These steps include:
- Racking
- Cleaning
- Pre-treatment
- Anodizing
- Coloring (if necessary)
- Sealing
Parts must be properly racked before the anodize process begins. When on the rack, they can be properly cleaned, treated, and dipped into the tanks with precision.
It’s worth noting that nearly every part will be left with a small rack mark where contact between the metal is made. To minimize the effect, the best practice is to rack parts in unexposed areas that are not significant to the final product.
Parts are then cleaned to remove any impurities, grease, or surface dirt that could impact the anodized finish on the base metal. Depending on the process and the base metal, either an alkaline or acid cleaner is used.
Next comes the pre-treatment process. If the parts need a matte finish, an etching tool will be used to remove more surface imperfections and a thin layer of aluminum to ensure the final finish will be as smooth as possible. If the parts need to be brightened, the objective is the same but it is done with a different chemical mixture.
The anodizing process begins by using the acid electrolyte bath to create an electrical current that passes through the aluminum part. This is where the anodic oxide film will be created on the surface layer of the base metal.
Inside of the tank, there is a cathode present, and the physical aluminum piece being dipped into the tank acts as the anode. This allows the oxygen ions being released from the electrolyte solution to integrate with the aluminum.
If the part requires coloring, the rack pieces will be moved to a new tank with a dyed chemical and immersed into the solution similar to the previous step. However, this step will be focused on only applying a color since the anodic oxide film has already been applied.
The last and most important step to complete the anodize process is sealing. There are three types of sealing that can be done including hot deionized water sealing, mid-temperature sealing, and cold sealing. Sealing ensures the part will have maximum corrosion resistance properties.
This is a standard anodize process but steps can be interchanged, removed, or added based on the base metal, alloys, coloring, anodize type, and quantity of parts.
Types Of Anodizing
Anodizing is a surface treatment process in which anodic oxidation changes the properties of the metal surface.
Types I, II, and III are different in what they achieve and how they work. There are also two different classes (Class 1 and Class 2) that are combined with these anodizing types to manipulate the type of finish.
Type I – Chromic Acid
Type I Chromic Acid Anodizing creates the thinnest oxide film layer of any anodize process. The oxidation is non-conductive and is commonly referred to as a base finish or those metal products that cannot handle too much of a thickness change.
The typical thickness ranges between 0.00005” to 0.0002”. While this is a minor change compared to other anodize types, this will still significantly increase corrosion resistance properties and provide added protection.
Type I anodize will not decrease the fatigue strength of the base material and uses hot water or sodium dichromate to seal the finish. If your parts demand more flex, Type I anodize may be the right option for you.
Properties & Characteristics
- Corrosion resistance
- Dielectric oxide film
- Chemically active oxide film for paint adhesion
- Improved bond strength
- Non-conductive
- Black dyed finish
- Tight tolerance with minimal dimension change
Type II – Sulphuric Acid
Type II Sulphuric Acid is probably the most common anodize process because it can cover a broad range of finishes, color types, and base metal alloys. It provides a harder, more durable finish than Type I with a more defined aesthetic look.
The thickness range is between .0001″-.001″ with a 67% penetration into the metal substrate. This leaves 33% over the original metal layer causing an expansion in the dimension of the original surface.
This anodizing process is best used on parts that need to improve overall hardness, abrasion resistance, and other external stress resistance on the surface. Without color or a proper seal, it does contain porous properties making it most effective when combined with a color dye for a firm seal.
Properties & Characteristics
- Harder finish than Type I
- Corrosion resistance with 336 + hours of salt spray resistance
- Surface durability
- Excellent dyeability
- Electrical insulation
- Aesthetic improvements
- Increased abrasion resistance
- Flame resistance
Specifications
- MIL-A-8625F TYPE II CLASS 1 (Non-Dyed) and CLASS 2 (Dyed)
- MIL-STD-171
- ASTM B580-79 (TYPE A)
- AMS 2468 & 2469
Type III – Hardcoat Anodize
Type III Hardcoat Anodize is a much more dense finish with the highest wear resistance properties of any anodize finish. The finish can also be manipulated well to adhere to tighter tolerances.
Hard anodize thicknesses range from 0.0005 to 0.0030” but the exact number will depend highly on the base metal alloy that is being finished. With hardcoat, 50% of the coating will penetrate the surface leaving the other 50% left to build up onto the surface layer of the metal.
There are alternative finishes that can be done too like Type III with PTFE. This is a similar process with Teflon added to improve lubricity, wear resistance, and corrosion resistance. All Type III finishes are electrical insulators too.
Properties & Characteristics
- Unmatched wear properties
- Coatings wear as well as or better than hardened steels
(HRC values of 70) as judged by Suga and Taber wear tests - Can achieve salt spray resistance in excess of 1000 hours
- Can achieve very tight tolerances
- High dielectric strength to 2000VDC
- Heat dissipation
Specifications
- MIL-A-8625F TYPE III CLASS 1 (Non-Dyed) and CLASS 2 (Dyed)
- MIL-STD-171
- ASTM B580-79 (TYPE A)
- AMS 2468 & 2469
Class I vs Class II Anodizing
Class 1 and class 2 anodizing is a method to codify the specification of anodized aluminum using a specific process. The key difference between the two classes is the thickness applied to the base metal and whether a color dye is added into the process.
These two anodize classes should not be confused with the three types of anodizing. Instead, they are combined to indicate a more specific finish. For example, Type III Class II anodize refers to hardcoat anodize with dye.
Class I
This class is known as a high-performance finish best used for exterior applications. The minimum coating thickness is 0.0007” and there is no dye used in this class of anodizing.
Class II
Class II anodizing uses a color dye in the finishing process with a minimum coating thickness of 0.0004”. This is a more commercial anodize with a softer surface than class I, designed for less vigorous environments.
What Metals Can You Anodize?
Aluminum is the most common metal that can be anodized and popularly used because it typically responds the best to the different anodize processes.
Some other metals that can be anodized are magnesium, zinc, and titanium. The key is that these metals are nonferrous and are able to react properly with the acid electrolyte bath.
Anodizing changes the surface of aluminum by making it more corrosion resistant and better able to resist scratches. This is done by passing electricity through a thin layer of oxide at the surface of the metal, which causes new aluminum to grow on the surface.
Each metal will have a slightly different reaction during the anodizing process when considering factors like thickness and color.
Benefits Of Anodizing
Increased Durability
Anodize is used for aluminum alloys because they are highly susceptible to external damages. With anodizing, you can increase the durability of your parts by adding resistance to things like heat, corrosion, abrasion, and wear.
The anodizing process will increase the lifespan of your parts and eliminate regular maintenance required to keep the parts healthy and strong.
Improved Aesthetic
Anodizing is extremely versatile with many different colors and finishes types available to accommodate a variety of part and industry types. These finishes will improve the aesthetic look on your part giving you plenty of customization control.
Most importantly, the anodized parts will maintain their metallic appearance. This is not necessarily the case when you rely on alternative metal finishing options as a solution.
Lower Costs
Not only is the upfront cost for a traditional anodizing project affordable, but you are creating a more durable long-lasting part. By doing so, you are only decreasing the long-term costs required to maintain these parts because of the improvements in durability and wear resistance.
DiFruscia Industries, Inc. Anodizing
DiFruscia Industries, Inc. has been serving the anodizing industry for over 60 years with plenty of innovation and creativity to provide the most reliable finishes. We offer both Type II and Type III anodizing along with precision masking, sandblasting, and bright dip finishes to fit your needs.
Contact DiFruscia Industries, Inc to get more information about the anodizing process and how exactly it can benefit both you and your business. Request a FREE quote today!
