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Explaining the Differences Between Hardcoat and Other Anodizing Methods

by | Jul 27, 2023

Anodizing has revolutionized the durability and aesthetic appeal of metallic objects as a prominent surface treatment technology. Within the realm of anodizing, different methodologies exist, each presenting unique advantages and applications. One such methodology that has gained considerable recognition is hard coat anodizing.

Renowned for its exceptional hardness, remarkable wear resistance, and unrivaled corrosion protection properties, hard coat anodizing has emerged as a formidable contender in the field.

This article will explain the differences between hard coat anodizing and other anodizing methods and the benefits and applications of hard coat anodizing. It will also provide tips on how to clean and care for hard-coated anodized material and answer some common questions about the process.

Experience excellence in anodizing with Valence. With our state-of-the-art processing lines, we boast a diverse range of anodize capabilities. From tartaric-sulfuric anodize and boric-sulfuric anodize to chromic and hard anodize, we provide cutting-edge solutions for your specific requirements. Please contact us about our anodizing process or request a quote for you project.


What Is Anodizing?

Anodization is an electrochemical process employed to enhance the corrosion resistance of metals, primarily aluminum and titanium. By subjecting the metal to anodization, the surface undergoes a transformation, converting it into a metal oxide surface that effectively shields the underlying metal from oxidation. This protective oxide layer serves as a barrier against external corrosive elements, ensuring the longevity and integrity of the metal.

The anodizing process begins by immersing the metal object, called the anode, in an electrolytic solution. The object acts as the positive electrode, while a cathode, typically made of lead or stainless steel, serves as the negative electrode. An electric current is passed through the solution, causing oxygen ions to be released at the anode and react with the metal’s surface.


What is anodizing?

What Is Hard Coat Anodizing?

Hard coat anodizing, also referred to as hard anodizing or Type III anodizing, is an electrochemical process used to create a durable and wear-resistant surface on aluminum and other non-ferrous metals.

It is considered an advanced form of anodizing due to its ability to produce a thicker and harder oxide layer than standard anodizing techniques. This thicker and harder coating provides improved abrasion resistance, hardness, and corrosion resistance to the metal substrate, making it suitable for applications where enhanced durability is required.


What Is The Process Of Hard Coat Anodizing?

The process of hard coat anodizing involves immersing the aluminum part in a tank of an electrolyte solution, typically sulfuric acid. An electric current is then passed through the solution, causing a chemical reaction that forms a protective oxide layer on the surface of the aluminum. 

By adjusting the voltage of the current, one can effectively control the thickness of the layer. Once this step is completed, the part is taken out of the tank and submerged in a deionized water bath for rinsing purposes. 

To safeguard against corrosion and wear, the oxide layer is subsequently sealed using a dye or a sealant. Hard coat anodizing, as a process, can be swiftly accomplished within minutes, offering the ability to generate a robust and corrosion-resistant surface on aluminum parts.


What Are Other Types Of Anodizing Methods?

Hard coat anodizing is one of the most popular methods, but there are several other anodizing methods that may be suited to certain applications.


Conventional Anodizing

Conventional anodizing, also known as Type II anodizing, is a widely used electrochemical process for creating a protective and decorative oxide layer on the surface of metal parts. It is primarily applied to aluminum and its alloys, although it can also be used on other metals such as titanium and magnesium.

Conventional anodizing finds widespread applications in the automotive, aerospace, construction, electronics, and consumer goods industries. It is used for a variety of products, including architectural elements, electronic enclosures, automotive parts, cookware, and cosmetic packaging, among others.


Chromic Acid Anodizing

Chromic acid anodizing, also referred to as Type 1 anodizing, is an electrochemical process used to provide protective treatment for aluminum. It involves the use of chromic acid to create a thin, corrosion-resistant layer of aluminum oxide.

The process of chromic acid anodizing involves immersing the metal in a chromic acid bath and applying a direct current. This current causes the chromic acid to react with the metal, forming a thin oxide layer on the surface. The thickness of the oxide layer can be controlled by adjusting the current and the length of time the metal is immersed in the bath.

Compared to other anodizing methods, chromic acid anodizing produces the thinnest surface oxide layer. Despite its thinness, properly sealed Type 1 anodized coatings offer the same level of corrosion protection as the thicker Type II and Type III coatings.


Sulphuric Acid Anodizing

Sulfuric acid anodizing is a widely used method of anodizing that utilizes sulfuric acid as the electrolyte. This process results in the formation of a durable and corrosion-resistant coating of aluminum oxide (Al₂O₃) on the surface of the treated part. 

The sulfuric acid anodizing process begins by immersing the aluminum part in a bath containing a sulfuric acid solution and applying a current to the part. This causes the aluminum to chemically react with the acid, forming an oxide layer on the surface.

Sulfuric acid anodizing offers a clearer finish compared to other forms of anodizing. This clarity provides increased versatility when it comes to color dying, allowing for more vibrant and precise color options.


Sulphuric acid anodizing


Tartaric Sulphuric Acid Anodizing

Tartaric sulfuric acid anodizing (TSA) is commonly used as a pre-treatment for aerospace and defense paint systems due to its ability to conform with the latest REACH regulations, which aim to protect human health and the environment from the risks posed by chemicals.1

Compared to chromic acid anodizing, TSA does exhibit some differences in surface characteristics. TSA typically results in a slightly coarse grain structure and additional surface porosity. However, despite these differences, TSA still provides optimal adhesion for subsequent paint priming without compromising corrosion protection.


Differences Between Hard Coat And Other Anodizing Methods

Let’s explore the fascinating contrasts between hard coat anodizing and other anodizing methods.


Acid Type

Hard coat anodizing uses sulfuric acid with a small amount of an organic acid, such as oxalic acid, chromic acid anodizing uses chromic acid, sulphuric acid anodizing uses sulphuric acid, and tartaric sulphuric acid anodizing uses tartaric acid and sulphuric acid. The type of acid used in the anodizing process affects the thickness and properties of the anodized layer.


Anodizing Thickness

The thickness of the coating is a notable difference between anodized and hard anodized surfaces, and it plays a significant role in their respective properties. Hard coat anodizing produces the thickest anodized layer, providing several advantages, such as enhanced abrasion resistance and a more uniform surface, while other methods produce thinner and softer layers.


Hardness Of The Anodized Layer 

Hard coat anodizing produces an oxide layer that is much harder than the oxide layer produced by conventional and other anodizing methods. The hard anodized layer is much more durable and resistant to wear and tear. It can also withstand higher temperatures and is more resistant to corrosion.



Anodized aluminum undergoes a sealing process to close any pores that may form during the conversion to aluminum oxide. This sealing step provides a protective coating to the anodized aluminum, preventing color erosion in products that have been colored.

On the other hand, hard anodized aluminum, known for its thicker and more durable surface, is typically not sealed. The robust nature of the hard anodized coating makes a sealant unnecessary, as it already possesses excellent wear-proof properties.2


Benefits Of Hard Coat Anodizing Method

Hard coat anodizing offers a range of exceptional benefits, with its unparalleled hardness and wear resistance standing out as one of its primary advantages. By subjecting the metal to a meticulous and controlled anodizing process, an extraordinary transformation takes place, giving rise to an oxide layer of remarkable hardness that surpasses the inherent hardness of the base material.

This robustness ensures superior durability, making hard coat anodized components capable of withstanding harsh environments, rigorous usage, and prolonged wear and tear.

One of the fascinating qualities of the hard coat anodized surface is its impressive dielectric strength, which grants it outstanding insulation properties. This means that the oxide layer acts as an efficient insulator, effectively halting the flow of electric current.3 Interestingly, the thickness of the oxide layer directly impacts its resistivity, creating a correlation where a thicker layer translates to higher resistance.


Different Applications Of Hard Coat Anodizing

The exceptional attributes of hard anodizing make it an ideal choice for a wide range of industries, including aerospace, aviation, robotics, food manufacturing, military, medical, oil, and petrochemical.

The wear- and corrosion-resistant film generated through hard anodizing finds extensive applications in various sectors. In the aerospace and aviation industries, it serves as a protective barrier against the demanding conditions encountered by aircraft components. Likewise, in robotics, the hard anodized surface safeguards sensitive parts from wear and tear, ensuring optimal performance and longevity.

Furthermore, the food manufacturing industry benefits from the non-reactive and hygienic nature of hard anodizing, making it suitable for cookware and other food-processing equipment. The military and defense sectors rely on hard anodized components for their durability and ability to withstand harsh environments.


How To Clean And Care For Hard-Coated Anodized Material?

Cleaning and caring for hard-coated anodized material is essential to maintain its appearance, functionality, and longevity. Here are some helpful tips:

  • Regular Dusting: Remove loose dirt and debris from the surface using a soft, lint-free cloth or a feather duster.
  • Gentle Cleaning Solution: Use a mild cleaning solution of non-abrasive, pH-neutral dish soap or anodized aluminum cleaner mixed with warm water.
  • Avoid Abrasive Tools: Do not use abrasive pads, steel wool, or harsh scrub brushes that can scratch the surface.
  • Thorough Rinse: After cleaning, rinse the material thoroughly with clean water to remove any residue.
  • Protective Measures: Consider using a protective wax or polish designed for anodized aluminum surfaces to maintain the appearance and provide additional protection.

It is important to regularly inspect the hard-coated anodized material for any signs of damage or wear and tear. If any damage is found, it is important to have it repaired or replaced as soon as possible. This will help to ensure that the material remains in good condition for many years to come.


Which Method Is Best For Your Purpose?

When deciding which anodizing method is best for your purpose, it is important to consider the desired outcome and the application of the material. Hard coat anodizing is often the best choice for applications that require maximum wear and corrosion resistance, such as aerospace, automotive, and medical components. 

Conventional anodizing is a good choice for decorative applications, such as architectural elements. Chromic acid and sulphuric acid anodizing are often used in the electronics industry, as they provide a thin, uniform coating that is highly conductive. Ultimately, the best anodizing method for your application depends on your specific needs and requirements.


Learn More About The Different Anodizing Methods With Valence

Valence Surface Technologies, a leading provider of chemical processing services, invites you to embark on a journey of discovery to learn more about the fascinating world of anodizing methods. 

With our in-depth knowledge and expertise, we understand that selecting the right anodizing method is crucial to achieving the desired outcomes for your project. Whether you require Type I Anodize, Boric Anodize (BSAA), Tartaric Anodize (TSA), or any other specialized method, our team is here to assist you in making an informed decision.

We recognize that each project has its own distinct considerations, such as corrosion resistance, mechanical bonding, or specific environmental requirements. Our experts will work closely with you to evaluate your project’s unique needs and recommend the most suitable anodizing method to meet your objectives.

Don’t navigate the anodizing process alone. Trust our experienced professionals to guide you every step of the way. Contact us today to discuss your project. 


Final Thoughts

The versatility and range of anodizing methods available empower industries to enhance the performance, aesthetics, and longevity of their products, catering to diverse market needs. Continued research and innovation in anodizing techniques pave the way for further advancements, expanding the range of possibilities and benefits for industries worldwide. 

With a deeper understanding of these differences, professionals can make well-informed decisions to achieve the desired results in their applications, ensuring enhanced performance, longevity, and visual appeal of anodized products.

Take advantage of Valence’s comprehensive range of anodizing services today! Whether you’re looking to enhance durability, achieve a decorative finish, or protect against corrosion. Contact us to discuss your specific requirements and discover how our expertise can elevate your projects to new heights.

Expand your horizons and stay informed by exploring our captivating selection of blogs:



Is hard anodized better than aluminum?

Yes, It is generally more durable and corrosion-resistant than aluminum. Hard-anodized aluminum is created through an electrochemical process that results in a hard surface coating on aluminum. This treatment significantly enhances the durability of the metal compared to untreated aluminum.


Is hard anodized as good as stainless steel?

Both materials have their own set of advantages and characteristics that make them suitable for different applications. Hard-anodized aluminum might be preferred for its lightweight and heat conductivity in certain situations, while stainless steel may be chosen for its resistance to corrosion and ability to maintain a polished appearance.


Does hard anodizing wear off?

Under normal usage and proper care, hard anodizing is highly resistant to scratches, abrasion, and corrosion. It can withstand the rigors of everyday use in cookware, automotive parts, and other applications. However, prolonged exposure to harsh chemicals, aggressive cleaning methods, or abrasive materials can potentially affect the anodized surface.


How do you hard coat anodized aluminum at home?

The process typically requires a dedicated anodizing power supply, an electrolyte solution (such as sulfuric acid), and a suitable anodizing tank. Due to the complexities and safety considerations involved, it is not recommended to attempt hard coat anodizing at home unless you have the necessary expertise and equipment.


What temperature is hard coat anodized?

The temperature at which hard coat anodizing is performed can vary depending on the specific process and desired results. Generally, hard coat anodizing is conducted at relatively low temperatures compared to other anodizing methods. The typical range for hard coat anodizing temperatures is around 32°F to 50°F. 



  1. Tartaric Sulphuric Acid Anodising | Surface Treatment | Poeton. (2019, June 21).
  2. Leaf Group. (n.d.). The difference between anodized and hard anodized. eHow. 
  3. Anodizing for Electrical Insulation. (2023, April 6). Semano Inc.


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