The process of aluminum anodizing proves to be a highly durable post-treatment method. It is the case since it enhances the appearance and performance of the anodized aluminum part. Besides, the process also helps better bond the primer and glue. As a result, aluminum has become one of the most popular and widely used materials for this reason alone in the present-day industry. Today, it produces several consumer, industrial, and commercial products.
What Is Anodized Aluminum?
When regular aluminum is treated, we obtain anodized aluminum with additional and remarkable durability. Mainly, here we are talking about the electrochemical process. It is used to immerse the metal in several electrolysis tanks. The anode layer of aluminum oxide in one of those tanks gets developed from the metal itself. Therefore, that is how anodic aluminum oxide is produced.
Being an electrochemical process, anodizing works by transforming the surface of the metal into an anodic oxide layer that is decorative, durable, and corrosion-resistant. While being made from aluminum itself, the layer highly controls the oxidation problem. It is because of the natural features of aluminum as a metal, unlike paints and coats used for the same. Moreover, it also means that the rugged and durable oxide coat of anodized aluminum will not peel off.
Apart from that, it will also not suffer wear down if kept under normal conditions. Aluminum is the choice of today’s market from non-ferrous metals that can be anodized. Along these lines, aluminum is much more widely used than zinc, titanium, and magnesium. After anodizing, aluminum holds three times the hardness compared to raw materials. Likewise, anodized aluminum is 60% lighter than other commonly used metals, such as copper and stainless steel.
Anodizing Aluminum Parts: How It Is Done
Anodizing aluminum parts starts with proper cleaning and rinsing the piece’s surface. The aluminum part is then placed in an electrolyte containing sulfuric or chromic acid. The acid reacts and forms tiny pores, or nanopores, on the aluminum surface, which is a sign of the formation of Positive ions, along with Negative ion conductive coating. When the process of electrolysis begins by applying an electric current and adding a cathode, oxygen ions start to generate and release from the acid, combining with the aluminum along the way.
A barrier layer forms when the aluminum surface combines with the negatively charged ions. This barrier layer is called the surface layer, making the aluminum part corrosion-resistant. Indeed, the anode coating comprises hydrated aluminum oxide, which is corrosion and abrasion-resistant. This conventional coating is usually of a thickness ranging between 0.1 mils and 1.0 mils. Meanwhile, color can be applied if needed. A sealant is used to close any micro-cracks in the oxide layer.
The holes of the part are injected with paint during the coloring process. But then again, the sealant is applied to seal the surface to retain the selected color. It is done after the colored pigment has reached the surface. The color does not fade, is durable, and is scrape and scratch-resistant. Furthermore, the color can only be eliminated by grinding off the substrate.
Anodizing Aluminum Parts: Types of Process
Aluminum anodizing exists in several types. Certain types result in a unique anodic coating. The most common ones are Type I-Chromic Acid Anodize, Type II-Sulfuric Acid Anodize, and Type III -Hard Anodize or Hard coat. Let’s have a look at them.
Anodized Type I – Chromic Acid Anodize
Anodized type I uses chromic acid to produce a thin and ductile anodic oxide layer on aluminum parts, hence the alternate name. It usually carries a surface thickness ranging from .00002 inches to .0001 inches, which means 20 to 100 microinches. Eventually, it regulates the utilization of chromic acid anodizing for decorative finishes. Apart from that, it is ideal for parts with strict tolerance requirements and where the size of the piece plays an important role. However, chromic acid is not safe for the environment, hence seldom used today.
Anodized Type II – Sulfuric Acid Anodize
It refers to the standard type of anodizing, where it utilizes sulfuric acid instead of chromic acid. The use is based on the military specification MIL-A-8625. Anodized type II is the standard specification for industrial anodized aluminum. Consequently, it is widely used as a standard in the aerospace, medical, military, and defense fields globally. In applications where hardness and wear resistance play a key role, sulfuric acid anodizing is mainly used.
This anodizing has a thickness range between .0001 inches and .001 inches. 67% of the total thickness of the formed coating is penetrating in the substrate. In comparison, 33% is additional length to the original part, making it more appropriate for coloring. The components may be treated mechanically or chemically, giving them a matte, non-reflective effect.
Anodized Type III – Hard Coat
Similar in terms of the process to type II anodizing is type III anodizing, also known as hard coat anodizing. The coating produced by a sulfuric acid-based electrolyte is much thicker and denser. Meanwhile, the two mils of thickness make it more corrosion and wear-resistant. The protective oxide layer penetration ratio to surface deposition is half by half.
Applications of aluminum parts where wear and tear can be extreme are where hard coatings are ideal. Corrosive environments requiring harder, thicker, and more durable layers also favor hard coatings. This type of coating also makes it a better insulator of electricity.
Type III is different from Type II based on the temperature and operating voltage of sulfuric acid solution electrolysis. The former is lower, and the latter is much higher.
Benefits of Anodizing Aluminum Parts
Due to changes on the molecular level in the base aluminum material thanks to the polar oxidation, the anodized aluminum parts neither chip nor peel off, carrying resistance to corrosion and wear-down. These molecular changes make anodized aluminum three times harder than its standard counterparts. It will not chip, peel, or flake even after color enhancement. Also, the product does not show rust, bronze, or aging due to the controlled aluminum oxidation process. There are no parts present in today’s market that are as tough and versatile as anodized aluminum parts.
High Value and Low Cost
Aluminum, in general, and anodized aluminum, in particular, is a very lightweight metal compared to other metal products. Ultimately, it results in it having much lower transportation costs. Compared to steel, zinc, copper, bronze, and brass, anodized aluminum holds a lower cost per square foot due to its high strength-to-weight ratio. Visually, it does not lack behind any of the metals mentioned above. At the same time, the service life of anodized aluminum is also longer than similar metal parts that are sprayed or electroplated.
While rich in recyclability and the only 100% entirely recyclable metal, aluminum is the most environmentally friendly metal. Similarly, its anodizing processes are eco-friendly, unlike spraying or electroplating, producing hazardous waste.
As mentioned earlier, aluminum is a lightweight metal. Simultaneously, anodized aluminum is around 60% lighter than stainless steel, brass, or copper. Henceforth, the transportation of aluminum proves to be more cost-effective and thus can solve many design problems. Anodized aluminum has proven ideal and versatile when used in several sectors where lightweight and durable solutions are required, such as architecture and aircraft.
The parts made of anodized aluminum are easy to maintain. The reason is that they can be cleaned easily with soap and water or mild detergent to remove dirt and restore the part’s finish effortlessly.
Anodized aluminum’s bright new silver color is far more beautiful than anything else. This color, found in its natural state, can be anodized while retaining a matte or bright finish. Custom textures can also be given to your product for a unique look and feel, apart from the default silver.
Customized Color Options
The open-pore structure of the anode layer before applying sealant allows for anodized aluminum to be processed quickly. This feature makes it available in any color possible – any brand you visualize. With no risk of weathering, the metal can likewise be colored to take on the appearance of any other metal while retaining its own physical and chemical properties. These other metals may include gold, copper, bronze, stainless steel, and brass.
Enhanced Abrasion Resistance
While being a metal oxide instead of a metal in terms of chemical structure makes the anodic oxide film have strong electrical insulation. It is undoubtedly required in some aluminum products, such as for a capacitive dielectric layer. Well, to achieve this, we need anodic oxidation.