2024:Aluminum Anodizing, Processes and Details You Need to Know
Anodizing is a kind of surface finish to protect your custom metal parts against corrosion, resist scratching, and enhance aesthetic quality. It is one of the most durable surface finishes available for metal parts. Anodized aluminum is widely used in many different industries in 2024. Today let’s have a look at aluminum anodizing, processes, and details that will help to show why anodizing is so popular and critical.
In architecture, aluminum anodizing is used to increase the structural stability and strength of roods, exterior surface panel, window frames, and more. In the automotive industry, aluminum anodizing is used to protect the exposed aluminum parts. For some products, we see in our daily life like MP3 players, cameras, and more, aluminum anodizing is used to increase the strength of the outer castings. In the food and beverage industry, pots, pans, and other cookware and utensils are beneficial from aluminum anodizing. In industrial manufacturing, anodized aluminum is used in plant equipment such as conveyors, electrolytic, capacitors, scales, and more.
What Is Anodizing Process?
Anodizing is an electrochemical process that converts the surface of the metal into a durable, corrosion-resistant, decorative and anodic oxide finish. Anodizing increases the thickness of the natural oxide layer on the surface of the metal. Metal parts are treated forms the anode electrode of an electrolytic cell so the process is called anodizing. Anodizing increases resistance to corrosion and wear. It offers better adhesion for primers and glues. Anodic films are used for many effects. For example, cosmetic effect with thick porous coasting which can absorb the dye, and cosmetic effect with transparent coasting which adds reflected light wave interference effects. Anodic films are commonly applied to protect aluminum alloys. Anodizing process exist for titanium, zinc, magnesium, niobium, zirconium, hafnium, and tantalum. Anodizing changes the microscopic texture of the surface and the crystal structure of the metal. A thick coating is porous normally. So, a sealing process is usually needed to achieve corrosion resistance. Anodized aluminum surface is harder than aluminum but has low to moderate wear resistance which can be improved by increasing the thickness or by applying sealing substances. Anodic films are stronger than most types of paint and metal plating. At TEAM Rapid, you can use our anodized aluminum to enhance the functionality and appearance of the metal parts. Anodizing can be done on a wide range of materials. Today, we will talk about anodized aluminum. Here are the things you need to know about anodizing aluminum.
What Is Aluminum Anodizing?
Aluminum anodizing is an electrochemical passivation process. The surface layer of an aluminum substrate is converted to an aluminum oxide layer. There is a natural oxide layer on aluminum which is usually uneven. The thin oxide layer provides poor protection. The application control of the electrical charge in an acidic electrolytic bath creates a regular and uniform layer which increases durability, wear resistance, and corrosion resistance. Also, the anodic layer can be used for secondary processing to incorporate functional materials like color and lubricants. There are many processes and standards that used anodized aluminum. The most common one is used in the defense, aerospace, and automotive industries. In United State, MIL-A-8625 is the most often cited anodizing specification. MIL-A-8625 defines aluminum anodizing as Type I–Chromic acid anodizing, Type II – Sulfuric acid anodizing, and Type III – Sulfuric acid hard anodizing.
How Is the Aluminum Anodizing Process?
When preparing aluminum for anodizing, ensure the surface is cleaned and rinsed. And then place it into a bath of some electrolytic solution like sulfuric acid. How does the anodizing aluminum process work? When the process is ongoing, a positive electric charge is sent through the aluminum and a negative charge is applied to plates in the electrolyte. How the electrolyte is an electrically conductive solution? A positive electric charge is applied to the aluminum to make it an anode. A negative charge is applied to plates that are suspended in the electrolyte. The electricity in the circuit creates positive ions to be attracted to the negative plates. The electricity in the circuit creates positive ions to be attracted to the negative plates. And negative ions flock to the positive anode.
Summary–generally, the aluminum anodizing process is like this:
1, An electrolytic solution bath is set up. This will be or will not be enhanced with dyes.
2, The metal like aluminum is immersed in the electrolytic solution.
3, When the metal is immersed, a direct current is passed through the electrolytic solution to release oxygen and hydrogen.
4, When the process happens, the oxygen reacts on the surface of the metal. It acts as an anode when the hydrogen act on its surface as a cathode. This reaction happens as a build-up of aluminum oxide.
Barrier Layers In Anodizing Aluminum
The electrochemical reaction causes pores to form on the surface of the aluminum because excess positive ions escape. The aluminum at the surface combines with the negatively charged O2 ions to create aluminum oxide. This is the barrier layer that defense against further chemical reactions. The pores will continue to penetrate deeper into the substrate. For non-hard coatings, the depth can be more than 10 microns. When this level is done, if it is no need to add color, the process is stopped and the surface can be sealed by rinsing in water. You will get the hard and natural aluminum oxide coating which withstands chemical attacks and is scratch resistant.
Hard Anodizing
Hard anodizing is also called type III. This method also used sulfuric acid. It produces a thicker anodized layer. Hard anodizing is suitable for coloration. It provides greater corrosion protection and resistance to wear in hard environments. Hand anodizing needs more time and it is more expensive. It creates superior results.
Does Aluminum Need to Have Corrosion Protection?
Anodize aluminum can deteriorate in the presence of oxygen although aluminum does not rust. Oxygen is reactive. When the aluminum parts are exposed to the atmosphere, a layer of aluminum oxide is formed on the surface which protects against corrosion. Aluminum withstands more than just pure water and air. Acid rain and salt water can exploit weaknesses on the surfaces of anodized aluminum.
How to Have Color Aluminum Anodizing?
Colored anodize aluminum is increasing need when it comes to anodizing. The pores etched into the surface are ideal for introducing tints or pigments. The pigment fills the empty pores up to the surface. Anodized colors are durable. The color can not be scratched off from the surface as the colors are deep down. It can be removed only by grinding away the substrate.
Anodized Aluminum Has a Metallic Sheen
After adding color to the anodized aluminum, it has a characteristic metallic look. It is caused by the uniform electro-chemical etching; a rough surface is left behind. The surface is rougher and the colors are more durable when the pores are deeper. Light striking the surface parts interact with the colorant and partly with the uncolored metal.
Other Materials Can Also Be Anodized
Anodizing can work with other materials like magnesium, titanium, and conductive plastics. Anodizing process is not expensive. It is reliable and durable. Anodizing process is widely used in architectural fittings as it is beautiful and impervious to the effects of weathering.
Titanium
In jewelry and other decorative product industry, aluminum anodizing is widely to use improve the products. Anodized titanium is used with wedding bands increasing as it is hard and elicits a low allergic response.
Tantalum
Anodized tantalum is used to make capacitors and decorative. Tantalum can be manipulated or anodized to exhibit a wide range of colors. By changing the anodizing voltage and temperature, the film thickness can be controlled. Normally, the thickness of the anodized tantalum film ranges from 18 to 23 angstroms per volt.
Niobium
Anodized niobium is used for decorative purposes. Anodized niobium is an element of commemorative coins and jewelry. Similar to tantalum, anodized niobium can be in a wide range of color and film thickness.
Zinc
Zinc services with alternative methods. Zinc is not often anodized. But when it is anodized, the process is introduced by the International Lead Zinc Organization to achieve olive-green zinc which is hard and corrosion resistant.
Magnesium
Magnesium is a fairly regular basic anodized material. Manufacturers seal magnesium with oil, wax, and other similar materials. Anodized magnesium is widely used as a primer paint.
It Is Impossible to Anodize the Whole Part?
Anodizing requests a part is immersed in a series of chemical baths. The parts should be hung to keep them from failing to the bottom of the tank. When the holding fixture touches the parts, the anodizing chemicals will not work right. So, it is better to design a place on the part that can be used for hanging.
What Benefit does Aluminum Anodizing Offers?
Anodizing aluminum process is widely used for a wide range of applications. For example, you will find anodized aluminum parts in aircraft, consumer goods, sports equipment, electronics, and more. Anodized aluminum parts are durable and hard. As anodized aluminum parts are abrasion resistant and corrosion resistant, they are suitable to be placed in harsh environments. It also provides thermal insulation to metal products. The anodized aluminum process makes metal parts last longer than raw parts. The coating is thinner than paints and powders. Anodizing aluminum parts have an eco-friendly finish, it is recyclable. Compared to painting and powder coating, the post-processing technique is affordable.
Design of Anodized Parts
When you want to have a anodize aluminum part, you have to think about a number of factors of the application. For example, the thickness, hardness, and color of the desired film. According to these factors, you can decide on details, solution composition, electrolyte concentration, solution temperature, acidity, and current voltage. If you want harder and thicker films, you need to use weaker solutions coupled with higher voltages and lower temperatures. If you want thinker and softer films, you will use a stronger solution coupled with lower voltages and higher temperatures.
Machines for Anodized Process
To anodize materials, manufacturers need a different system. Here at TEAM Rapid, we offer customers anodize kits, we use anodize equipment which includes anodizing rectifiers and anodizing rectifier controllers.
1, Anodizing Rectifiers
Anodizing rectifiers convert AC into DA. This direct current is used to anodize parts that are corrosion-resistant.
2, Anodizing Rectifier Controller
Anodizing rectifier controllers allow for manipulation of anodizing operations. Anodizing rectifier controllers are paired with CNC technology and computer programming. With these, anodized parts can be created with precise layering and colors.
Similar Processes
Here at TEAM Rapid, we use chromic acid anodization (Type I), sulfuric acid anodizing (Type II), and sulfuric acid hard coat(hard coat) anodizing, or hard anodizing (Type III) to perform anodized aluminum projects.
Type I
This is the oldest and the most used anodize process. During this process, a reactive metal is matched with an electrolytic process that used chromic acid. The anodizing is initiated by attaching an oxygen-producing anode to the metal which is being treated and immersed into an electrolytic solution. The voltage of the current is increased as the anode creates oxygen and creates an oxide film. Type I is great for anodizing. The thickness of aluminum is reduced just by 0.02 to 0.04 mils which is less than the rates of reduction possible with other types. Type I is harmful to the environment.
Types II and III
Type II and type III use another corrosive solution, a sulfuric acid solution. This solution is an acid formed from sulfur dioxide and is dense and oily. Type II and type III processes are similar, but the performance temperature and current density are different. Bright dip anodizing is a notable subtype of type II anodizing.
Bright dip anodizing
If the aluminum needs to be brightened to a level of luster, this process is used. Bright dip anodizing work best on raw aluminum.
Type III
Type III aluminum anodizing is performed under lower temperatures and higher electrical current density. It increases anodic growth and creates harder surfaces. Type I, II, and III can only be applied on aluminum and aluminum alloys. If you need to anodize non-aluminum metals, chromate conversion coating, clear anodizing, color anodizing, black anodizing, titanium anodizing and other custom anodizing processes can be used at TEAM Rapid.
Chromate Conversation Coating
Chromate conversion coasting is different from anodizing. It allows the electrical conductivity of aluminum to remain intact instead of neutralizing.
Chromate conversion coating uses hexavalent chromium or non-hexavalent chromium.
To avoid the issues attached to this categorization, many manufacturers use non-hexavalent chromium, an environmentally-friendly alternative coating material that meets the requirements of both the Restriction of Hazardous Substances and the European Union End-of-Life Vehicle recycling directives.
Clear Anodizing
Clear anodizing is the common type of anodize coating. During this process, sulfuric acid and hot water seal is used in the end. Clear anodizing is often used for automotive applications.
Color Anodizing
Color anodizing is used in aesthetic applications. This process is usually used after a piece’s initial anodization and sealing. Metallic salts or organic dyes are used to achieve yellow, white, and black colors.
Organic Anodizing
Organic anodizing is used when organic acids are used. At TEAM Rapid, we use this process very carefully as these acids will cause the current to treat the aluminum with unusual aggression. This treatment will cause pitting or scarring.
Aluminum Anodizing Service for Your Custom Metal Parts
TEAM Rapid is able to offer advice on the many different finishing services including aluminum anodizing service, painting, silk printing, etc. for your rapid prototyping and low-volume manufacturing needs. Our engineers will help you to find the rapid manufacturing solution that fits your time, and budget to market, let’s get started today!
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