Anodized aluminum is a type of aluminum that has been chemically treated to create an extremely resistant finish. Employing an electrochemical technique, anodized aluminum is made by immersing the metal in a series of tanks, one of which contains the anodic layer that is produced from the metal itself.

This anodized layer is much more resistant to corrosion than any other similar product on the market since it is made from the metal itself, instead of being painted or coated. It also won’t ever chip, flake, or peel. In addition to being 60% lighter than other metals like copper and stainless steel, anodized aluminum is three times more durable than raw aluminum.

Continue reading to discover all you need to know about this anodized aluminum.

What is the process of anodizing aluminum?

Aluminum is carefully cleaned, rinsed, and then submerged in an electrolytic solution, such as sulfuric acid, to prepare it for anodizing. An electrolyte is a solution that conducts electricity and has a lot of positive and negative ions that it is looking to exchange.

The aluminum becomes the “anode” after receiving a positive electric charge, whereas the plates hung in the electrolyte receive a negative charge. In this circuit, the electric current attracts positive ions to the negative plates and attracts negative ions to the aluminum anode, which serves as the positive anode.

What does an anodizing barrier layer do?

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As extra positive ions leave the aluminum surface during the electrochemical reaction, pores start to form. As they erode deeper into the substrate, these pores arrange themselves into a geometrically regular pattern.

Aluminum oxide is produced at the surface when negatively charged O2 ions interact with aluminum. A barrier layer is created in these areas as protection against additional chemical reactions.

As long as current is supplied, a sequence of hollow structures that resemble columns will form as the relatively reactive and weak portions of the pores keep working their way deeper into the substrate. When an electric current comes through, it creates a regular pattern of surface porosity.

The level of penetration of these columns increases as the current is delivered for a longer period. The depth can reach 10 microns for normal non-hard coatings.

If no color is required after reaching this level, the process is stopped, and the surface can be sealed by simply giving it a quick rinse in water. You’ll be left with a durable, natural aluminum oxide coating that is scratch- and chemical-resistant. On the Mohs scale of hardness, aluminum oxide ranks just behind diamond at 9 out of 10.

How does hard anodizing work?

Hard anodizing, also known as Type III, provides better corrosion protection and wear resistance in abrasive settings or when used on moving mechanical parts that are prone to heavy friction.

This is created by maintaining the electrical current until the pores are at least 25 microns or greater in size and have a depth greater than 10 microns. This costs more money and requires more time, but the outcome is better.

Does aluminum require corrosion protection?

Although aluminum does not rust, it can deteriorate when exposed to air, a process known as oxidation. What exactly is oxidation? Simply put, it refers to a reaction to oxygen.

And oxygen is extremely reactive, easily creating compounds with the majority of other elements. Aluminum quickly develops an aluminum oxide coating on its surface when exposed to air, and this layer offers some degree of defense against further corrosion.

However, aluminum must be resistant to more than simply air and water. The surface passivation still has gaps that can be exploited by acid rain, salt water, and other pollutants. Even modern alloys will respond differently to this environmental exposure, varying from simple surface browning to mechanical failure.

How is color added to the metal anodizing process?

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When most people think of anodizing, they typically picture colored aluminum. The fine, stable pores carved onto the surface are suitable for inserting colors or pigments.

When the pigment reaches the surface, it seals off all the open holes there. Since the colors are embedded deep inside the anodized coating, they can only be removed by grinding the substrate, which is why anodized colors are so resistant to scratching.

Why does anodized aluminum consistently have that unique metallic sheen?

Anodized aluminum has a distinctive “metallic” appearance after coloring. Two things are responsible for this. One is that a rough surface is left behind as a result of homogeneous electrochemical etching. Although the surface will be coarser and the pores deeper, the colors will be considerably more lasting.

Second, various reactions between the colorant and the top, uncolored metal occur when light hits the surface. As it reflects off an anodized surface, light takes on many hues. As a result, the light that reflects and hits your eye will actually be made up of two separate wavelengths that interact as they do so. This is what gives aluminum anodizing its characteristic luster.

Can other materials be anodized besides aluminum?

Magnesium, titanium, and even conductive polymers can all be anodized. It is reasonably priced, dependable, and quite durable. Because it is both lovely and remarkably resistant to the effects of weathering, it is utilized so frequently in architectural fittings.

Why is it difficult to anodize a whole part?

Anodizing entails immersing a part in several types of chemical baths. Holding a part in place necessitates mounting it on some sort of hanger to prevent it from slipping to the bottom of the tank.

Wherever the holding fixture comes into contact with the part, that area will be blocked, and the anodizing chemicals will not perform correctly. Because of this, it’s a good idea to build a space for holding that won’t detract from its aesthetic appeal.


Anodizing can be applied to both aluminum and steel and even helps with corrosion prevention. If those qualities aren’t enough for you, anodizing provides a non-reflective finish (which makes it great for outdoor applications), reduces the weight of aluminum by up to 40%, and can increase its hardness.

So whether you’re interested in decorative finishes or functional improvements, anodized aluminum definitely has something to offer you.

Would you benefit from adonized aluminum?

For a free quote and project assessment, please get in touch with us. We’ll be happy to discuss the many various finishing services we provide.

Our experts will work with you to identify the best option for your needs in terms of price, time to market, and desired outcomes. Contact SEI Castings today at