How to Anodize Aluminum Parts: The Complete Guide

This article will explain to you in detail what anodized aluminium is, its advantages, how it is anodized, its different types, etc. It will also help you choose the right anodized aluminium process for you. I hope it will be helpful to you.

What is Aluminum Anodization?

Anodizing is a common surface treatment process that is applied to a wide range of metal materials, but the most commonly used is aluminium. Aluminium anodizing is done by placing the aluminium product into an acidic electrolytic solution and then passing an electric current through it, allowing the aluminium piece to act as an anode and react with the electrolyte in an oxidizing reaction, forming an alumina layer and adsorbing it firmly to the surface of the aluminium piece.

The aluminium oxide layer formed by anodizing is not easy to come off compared to the naturally formed one and has a higher hardness, and resistance to abrasion and corrosion.

Why Use Anodized Aluminum?

Corrosion Resistance

The first reason to use anodizing on an aluminum part is to increase its corrosion resistance, for example, if you are using an aluminum part that will be exposed to the outdoors, seawater or some extreme conditions for a long time, then you need to increase its corrosion resistance. Anodizing is a great option for this.

Friction Resistance

Aluminum is a relatively soft metal and is not abrasion resistant, but it can be anodized to improve its abrasion resistance, making it less susceptible to wear and tear and increasing its service life.

Artistic

If you need to decorate with aluminium products, then you can also choose to anodize. Through anodizing, you can get aluminium parts with rich colours, which can improve the quality of the surface of the aluminium parts and decorative and make it more beautiful.

Electrical Insulation

If you need to use aluminium for electronics or electrical equipment and don’t need the conductivity of aluminium, then you can improve the insulating properties of the aluminium metal by anodizing it, thus reducing the problems that occur due to conductivity.

How to Anodize Aluminum

The next section will take you through how anodizing is done step-by-step, as well as the materials it requires and the precautions to be taken.

Materials and Equipment Required

• Aluminium products: Aluminum products to be treated, such as aluminium alloy plates, profiles and parts. This is the main character so it is indispensable.
• Electrolytic tank: A container used to hold the electrolyte and the aluminium product. Its size depends on the size of the aluminium product.
• Electrolyte: Electrolyte required for anodizing, usually including sulfuric acid, oxalic acid, chromic acid, phosphoric acid, etc.
• Power supply equipment: Provide electric current to promote the oxidation reaction on the surface of aluminium products.
• Cathode material: Needed to form a complete pyrolysis system with an aluminium product as an anode, usually lead or stainless steel.

Steps of Anodizing

• Preparation: Clean the surface of aluminium products of impurities such as oil, stains and naturally occurring oxides. Then prepare the required materials and equipment.
• Placing the aluminium product: Place the aluminium product in the electrolytic bath, making sure that the electrolyte completely submerges the aluminium product.
• Starting electrolysis: The electrolyte is heated to the right temperature, then the power is turned on so that the aluminum products act as anodes and direct current is applied so that their oxidation reaction begins.
• Control time and voltage: You need to keep an eye on the time and voltage during electrolysis so that you can control the thickness and quality of the aluminum oxide layer.
• Cleaning and post-treatment: After the anodizing is finished, at this time, you need to take the aluminium parts out of the electrolytic cell and then clean them to remove the residual electrolyte. Next, you can post-treat the aluminium parts according to your needs, such as sealing treatment, dyeing and so on.
• QUALITY CHECK AND PACKAGING: This step requires a quality check of the aluminium parts to see if they meet your requirements. If there is no problem, you can use it or package it for shipment.

Caveat

• Safe operation: In the process of anodizing, since corrosive liquid and electricity will be used, please make sure you wear protective equipment during the operation to avoid splashing of corrosive liquid or electric shock.
• Prevent air bubbles: In the process of oxidation, it is inevitable that air bubbles will stay on the surface of the aluminum parts, thus affecting the quality of oxidation, you can exclude air bubbles by stirring and other methods.
• Waste Liquid Disposal: After anodizing is completed, you need to dispose of the waste liquid properly to avoid damage to the environment.

How to Tell If Aluminum is Anodized

• Observe the appearance: after anodic oxidation treatment of aluminum surface of the oxide film color is more uniform, generally showing a silver-white or dark gray, if the color of the surface of the aluminum parts is uneven, mottled, that the probability is not after anodic oxidation.
• Hardness test: you can use a sharp object to scratch the metal surface, the anodized aluminum parts are harder and harder to scratch than the surface of ordinary aluminum parts.
• Conductivity test: For this test you only need an ordinary voltmeter. Anodized aluminum parts have a lower conductivity.
• Oxide layer: Anodizing will produce a layer of aluminum oxide with a thickness of 5~25um on the surface of aluminum parts, and the thickness is more uniform in each place. This is also a way to identify.

Different Types of Anodized Aluminum Processes

The anodized aluminum process can be broadly divided into four different types, all of which have different advantages, and the following will take you to understand each of these four processes:

Sulfuric acid anodizing

Sulfuric acid anodic oxidation refers to the use of sulfuric acid or aluminum sulfate as the electrolyte, the thickness of the generated oxide film is about 5~25um, this process is the most widely used, because it is a simple process, the cost is low, but it produces a general quality of the oxide layer, suitable for those who do not have any special requirements for the quality of anodic oxidation of the aluminum parts.

Oxalic acid anodizing

As the name implies, oxalic acid anodizing refers to the use of oxalic acid or aluminum oxalate as the electrolyte, which generates a thicker oxide film, up to 60 um. Compared with sulfuric acid anodizing, oxalic acid generates a better quality of the oxide layer, with higher corrosion and abrasion resistance, which can be used in occasions with higher quality requirements.

Chromic Acid Anodizing

The main component of chromic acid anodizing electrolyte is chromic acid, and the oxide layer generated by chromic acid is of higher quality than both sulfuric acid and oxalic acid, however, the oxide layer is very thin, usually only 2~5um, which is more suitable for aviation and automotive parts. However, it should be noted that chromic acid is toxic, so its process requirements are high, and safety should be observed during operation and handling.

Phosphate anodizing

The main component of phosphoric acid anodizing electrolyte is phosphoric acid. Aluminum parts oxidized with phosphoric acid have a uniform and bright surface. Compared with other types of oxidizing process, it is not a demanding process, and the requirements for equipment are not high.

How to Choose The Right Anodized Aluminum Process for You

Choosing the right anodized aluminum process is very important, but you can’t choose blindly, you need to choose according to your specific needs and the use of aluminum parts of the scene, the following is a few choice of anodized aluminum process you need to consider the aspects, you can refer to it:

Required performance characteristics

First of all you need to consider the performance of the aluminum parts you need, if you want wear-resistant and hardness aluminum products, then you can choose sulfuric acid or oxalic acid anodizing; if you want corrosion-resistant and heat-resistant aluminum parts, then you can choose chromic acid or phosphoric acid anodizing.

Areas of application and environmental requirements

The application areas and environmental requirements of aluminum parts are also aspects you must consider when choosing an anodized aluminum process. For example, if you need aluminum parts for automotive or aerospace, then you need to focus on its hardness and abrasion resistance; if you are in the field of architectural decoration or electronics, you need to consider its corrosion and abrasion resistance.

Cost and process complexity

Different anodized aluminum processes can vary in equipment, electrolyte and operation, which can affect their cost and process complexity. So you have to choose the right process according to your need for cost and process.

Regulatory and environmental requirements

Since some of the anodizing processes use toxic chemicals, you need to choose the right process according to local regulations and environmental requirements. When choosing a process, you also need to consider how to deal with waste liquids, gases and residues.

Design Tips and Considerations for Anodized Aluminum

Design Tips

• Oxide layer thickness: you determine the thickness of the oxide layer according to your needs, because different thicknesses of the oxide layer have different characteristics. (corrosion resistance, hardness, wear resistance)
• Size issues: When designing an aluminum part, you need to take into account that when it is anodized, its dimensions increase, so you need to allow for a certain margin when sizing the part.
• Structural design: You have to design the structure of the aluminum parts reasonably according to its specific use and working environment, to ensure that the oxidized aluminum parts can meet the characteristics you need.
• Color Selection: Since anodized aluminum parts can achieve many different colors of oxide layer, say so you need to determine the color at the time of design to avoid problems at a later stage.

Caveat

• Material Selection: Since different aluminum alloy materials can have an impact on oxide formation and performance, you need to know them in advance and select the right material or process.
• Temperature and Voltage: During the anodizing process, you need to control the temperature and voltage to ensure that the whole process is safe and controllable.
• Avoid surface damage: In the process of production, processing and transportation of aluminum parts, try to avoid scratches, collisions and other surface damage, thus affecting the quality of the oxide layer.

Applications of Anodized Aluminum:

Automotive

Anodized aluminum is often used in the manufacture of automobile housings, wheels, engine parts, doors, etc. Its corrosive and abrasion-resistant properties can withstand the wear and tear and corrosion that automobiles experience in a variety of different environments.

Aerospace

In the aerospace field, anodized aluminum is widely used in the manufacture of aircraft fuselage, engine parts, spacecraft shells and so on. Its light weight, high strength and corrosion resistance meet the stringent material requirements for aerospace vehicles.

Electronic Product

Anodized aluminum is also widely used in components such as housings for electronic products, battery cases, heat sinks, and thermal conductive plates. Its surface hardness and insulating properties make it an ideal material for manufacturing electronic products.

Outdoor Products

Anodized aluminum is also widely used in outdoor products, such as camping gear, mountaineering equipment, bicycle parts, and outdoor furniture. Its corrosion resistance, abrasion resistance and light weight can be applied to various outdoor environments.

How EVERGREEN Overcomes Quality Issues in Anodized Aluminum Parts

With more than 20 years of experience in anodizing aluminum, our company also has two experienced technical and quality control teams who can provide you with customized solutions and keep a strict eye on the quality of your products. Here’s a look at what they do in terms of quality in the anodized aluminum process:

Identify and Solve Common Problems

• Systematic quality management: establish a quality management system, including quality inspection, problem identification, corrective and preventive measures, etc., to ensure that quality problems can be handled and solved in a timely manner.
• Regular quality reviews: Regular quality reviews of production processes and products are conducted to identify common problems and take appropriate corrective action.
• Training and education: Training of production staff to improve their ability to recognize and solve quality problems and to enhance the quality awareness of the team.

Techniques for Obtaining Consistent and High-Quality Results

• Standardized process: We have developed a set of standardized process and operating procedures to ensure the consistency and stability of the production process and avoid quality fluctuations.
• Strict incoming material inspection: Ensure the use of high quality raw materials, strict control of raw material selection and procurement process to ensure product quality.
• PRECISION EQUIPMENT: We have precision production and testing equipment to ensure product processing accuracy and quality stability.

Maintain Proper Process Control

• Real-time monitoring and adjustment: We will identify and adjust any abnormalities in a timely manner by monitoring key parameters in the production process in real time to ensure that the product quality meets the requirements.
• Data Analysis and Improvement: Regularly collect and analyze production data to identify the root causes of problems and take improvement measures to continuously improve the stability and quality level of the production process.
• Reinforcement of quality inspection: We have established a strict quality inspection system, and carry out comprehensive testing of raw materials, semi-finished products and finished products to ensure that our products meet customer requirements and standards.

FAQ

How long does anodized aluminum last?

Generally speaking, anodized aluminum can last for several years or even more than ten years, and its duration depends on the thickness of the oxide layer, the quality and the environmental conditions. The thicker the oxide layer and the better the quality, the longer it lasts.

Is anodized aluminum prone to rusting?

Anodizing generates an oxide layer on the surface of the part, which prevents the aluminum part from oxidizing with outside air and water, and has a good function of rust prevention. However, if the oxide layer is damaged or of poor quality, the part will still rust. Of course, rust can also occur when parts are exposed to seawater or other extreme conditions for long periods of time.