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The beauty of metal "corrosion": anodizing process
2025-08-08
As the company continues to develop, the customer base will become more and more diverse, and customer demand for products will become more diversified. We will be exposed to more new surface treatment methods. Only the constant pursuit of excellence can drive us to continue learning and perfecting.Be good to yourself and keep pace with the development of society. Today we will mainly introduce one of the surface treatments for sheet metal - anodizing.
Anodizing is a metal surface treatment process, mainly used for aluminum and aluminum alloys. Among them, the anodizing process of aluminum and aluminum alloys is the most widely used. For example, the colorful power bank shells and the well-known Apple product series, such as the iPhone5, 5S, iPhone7 and other body shells, all use aluminum metal + anodizing process.
The advantages of anodizing are that it makes metal products both lightweight and durable, while also maintaining the metallic texture and colorfastness, resulting in a long service life. A variety of effects and textures can also be created on the surface.
So what is the principle of "anodization"?
Anodizing is the process of placing metals such as aluminum and its alloys in an acidic electrolyte solution and passing direct current through it, causing an oxide film to form on the metal surface. In simpler terms, the process involves technicians carefully manipulating the metal surface to "erode," creating an "anodized film."
Metals in the natural environment will produce a natural oxide film, which is not very useful for industrial processing. However, after the metal is anodized, a layer of "anodized film" will form on the surface, which can greatly improve the metal's performance.
Take aluminum alloy as an example. Its advantages are good processing performance and high specific strength, but its disadvantages are: low hardness, poor wear resistance, low melting point, and the operating temperature cannot exceed 200°... These disadvantages limit the processing and use of aluminum and aluminum alloys.
However, the aluminum alloy after anodizing treatment has greatly increased wear resistance, corrosion resistance, electrical insulation, thermal insulation, etc.
The effects after anodizing can be divided into natural color anodizing, single color anodizing, two-color anodizing, gradient color anodizing, etc. according to color; and can be divided into texture and glossy according to surface gloss.
Natural color anodizing: As the name suggests, it is an anodizing process that maintains the original color of the metal without any coloring treatment.
Monochrome anodizing: Only one color is used. It is the most widely used and most mature process. (The coloring process will be explained in detail later)
Two-color anodizing: also called secondary anodizing. This means a part is anodized twice, resulting in different colors and glossiness. For example, the iPhone 5 body and back cover logo:
4. How to determine the most reasonable tool setting point? What is the relationship between the workpiece coordinate system and the programming coordinate system? （1）The tool setting point can be set on the workpiece being processed, but please note that the tool setting point must be the reference position or the part that has been finely processed. Sometimes the tool setting point is destroyed by Cnc Processing(https://www.xmrex-tech.com/customized-cnc-machined-plastic-and-metal-parts-product/) after the first process, which will make it impossible to find the tool setting point in the second process and later processes. Therefore, when setting the tool in the first process, pay attention to setting a relative tool setting position at a place with a relatively fixed size relationship with the positioning reference, so that the original tool setting point can be found based on the relative position relationship between them. This relative tool setting position is usually set on the machine tool workbench or fixture. The selection principles are as follows:
a,It is easy to find the alignment.
b, Easy to program.
c, Small tool setting error.
Gradient anodizing: A process that has become increasingly popular in recent years, such as in e-cigarette casings (smoking is harmful to health, just an example). Gradient anodizing involves anodizing aluminum alloys and then applying multiple coloring and gradient treatments to achieve the desired effect.
Texture anodizing: After a process such as frosting and then anodizing, the surface of the metal product can achieve the desired effect.
Glossy anodizing: Glossy surface is also called "mirror surface", which usually undergoes a polishing process before and after treatment. For example, the glossy black process of iPhone 7.
Specific steps of anodizing
Pretreatment: mainly includes sandblasting, polishing and other treatments.
Decontamination and degreasing: remove oil stains on the surface of the workpiece to facilitate subsequent processing.
Alkali etching: Before anodizing, the metal has a natural oxide film. This step is to remove the previous natural oxide film.
Pickling: After the previous step, there will be a layer of grayish-white loose ash on the surface, which needs to be removed by pickling.
Chemical polishing: This refers to soaking the workpiece surface in a chemical solution, which can eliminate wear marks to a certain extent and make the surface smoother. The polishing here is not mechanical polishing. Although mechanical polishing is used as a pre-treatment before anodizing, chemical or electrochemical polishing is also used after anodizing to achieve a better surface treatment effect.
Re-deashing: After polishing, the surface of the workpiece will change color and accumulate dust due to corrosion by chemical solutions, so it needs to be deashed again.
Anodizing: Select an anodizing solution as needed for anodizing treatment. Currently, there are three main anodizing solutions: chromic acid, oxalic acid, and sulfuric acid. Sulfuric acid is the most commonly used, accounting for approximately 95% of anodizing operations on the market. "Anodizing" generally refers to sulfuric acid anodizing. Its characteristics include corrosion resistance, non-conductivity, excellent insulation, and easy coloring.
Activation: Enlarge the pores of the anodized film in preparation for coloring.
Acid removal cleaning: Clean the acid solution remaining in the previous steps to ensure dyeing quality.
Coloring: This is mainly done through electrolysis and chemical methods. Electrolysis uses an electric current and an electrolyte solution to treat the oxide layer, giving the metal a different color. Chemical methods use dyes to color the product.
Pore sealing: As mentioned above, the anodic oxide film has many tiny pores. After coloring, these pores need to be sealed. Otherwise, they will absorb other contaminants, easily attracting fingerprints and dust, resulting in poor corrosion resistance, affecting the surface appearance and service life, unless otherwise required.