Anodizing

Aluminum Anodized Finish （Aluminum Anodizing）

Brief introduction to the aluminum anodizing process

Anodic oxidation, also known as aluminum anodizing, refers to the electrochemical oxidation of metals or alloys. It is a process in which an oxide layer is formed on the surface of the aluminum and its alloys (anodes) under specific electrolyte and process conditions with the application of an external current.

There are three common types of anodizing for aluminum products: sulfuric acid anodizing, chromic acid anodizing, and oxalic acid anodizing. If not specified, sulfuric acid anodizing is usually referred to.

Here is a brief overview of Aluminum anodizing:

Common Substrates for Aluminum Anodizing:

Aluminum and its alloys: Common alloys include 2A12, 5052, 6061, 6063, 7075, etc. Cast aluminum alloys such as ADC10, ADC12, A356, and A380 are also commonly anodized.

Magnesium alloys: Primarily used for conductive oxidation/chemical oxidation, resulting in colors such as white and yellow.

Titanium alloys: Anodizing titanium alloys can produce various colors, including blue, yellow, green, gold, etc.

The thickness of Aluminum Anodizing:

The typical thickness of the oxide layer in Aluminum anodizing is around 10μm, ranging from 5μm to 15μm.

Functions of Aluminum Anodizing:

Protective: Increases surface hardness (HV300) and improves wear resistance.
Decorative: Creates various surface colors and effects.
Insulating: The oxide layer is non-conductive and provides insulation.
Enhances adhesion to organic coatings.
Improves bonding with inorganic coverings.

Colors of Aluminum Anodizing:

Colors for Aluminum anodizing include natural (silver), white, black, bright silver, gray, matte white, matte black, bright black, red, purple, yellow, green, gold, rose gold, and more. Virtually all colors can be achieved.

Note: The translation provided here is a direct translation of the text. Some terms, such as “ADC10” and “ADC12,” may refer to specific aluminum alloy designations and may vary based on regional standards.

02 | Aluminum Anodizing Process

Aluminum Anodizing Process:

Aluminum workpiece → Hanging fixture installation → Degreasing → Water rinsing → Etching with alkali solution → Water rinsing → Brightening → Water rinsing → Anodizing → Water rinsing → Deionized water rinsing → Dyeing or electrolytic coloring → Water rinsing → Deionized water rinsing → Sealing → Water rinsing → Removal from hanging fixture → Blow drying → Air drying → Quality inspection → Packaging → Shipping.

Note 1:

Various colors in anodizing can be achieved through two methods: dyeing and electrolytic coloring. Unless specified otherwise, dyeing is commonly used. Compared to dyeing, electrolytic coloring offers more durable, wear-resistant, and high-temperature-resistant colors (up to 400°C plating). Ordinary anodizing can experience color fading at such high temperatures.

Note 2:

The entire process of Aluminum anodizing can be completed within about 20 minutes (time may vary for higher thickness requirements). However, when performing black anodizing, the process can take over 2 hours or even up to 3 hours. Therefore, the cost of black anodizing is generally higher than that of Aluminum anodizing.

Note 3:

Pre-treatment processes for Aluminum anodizing usually include sandblasting or brushing. If the surface of the workpiece does not require high smoothness, sandblasting can effectively improve the adhesion between the oxide film and the workpiece, making it more durable and wear-resistant. Quartz sand is commonly used for sandblasting, including both automatic and manual methods (due to environmental requirements, many anodizing facilities outsource the sandblasting process). Different sand sizes are available, such as 50 mesh, 80 mesh, 100 mesh, 120 mesh, 150 mesh, 180 mesh, 200 mesh, 220 mesh, etc.

03 | Aluminum Anodizing Production Equipment Showcase

The production line includes fully automatic production lines (for small parts), overhead crane plating lines (for large and heavy parts), and manual lines (for small parts). It is capable of processing workpieces with a maximum length of 5 meters, width of 1 meter, and height (depth) of 2 meters.

In addition, the supporting facilities include an automatic sandblasting machine station and 15 manual sandblasting machines. There are also resources available for grinding, polishing, and high-gloss outsourcing services. The daily average production capacity exceeds one million units, ensuring sufficient production capacity.

04 | Aluminum Anodizing Display of Inspection Equipment

The components of aluminum anodizing detection equipment typically include handheld film thickness gauges, X-ray film thickness gauges, salt spray testing machines, hardness testers, and so on.

05 | Aluminum anodizing sample cases

Anodizing die-cast aluminum

Brief Introduction to Anodizing of Die-Cast Aluminum

Anodizing die-cast aluminum

Die-cast aluminum anodizing refers to the process of applying an anodized coating to aluminum parts that have been produced through the die-casting method. Die-casting involves injecting molten aluminum into a mold cavity under high pressure, forming complex shapes with excellent dimensional accuracy. Anodizing of die-cast aluminum refers to the process of applying an anodized treatment to die-cast aluminum alloys such as A356, ADC12, A380,ADC10, and DM6.

Colors for Die-Cast Aluminum Anodizing

Common ADC series and cast aluminum A356, A380, etc., are not suitable for producing colored anodized coatings. Typically, they are limited to natural colors (silver-white) and black. However, attempts to produce colors have been made, such as achieving a golden color on A356 through anodizing. However, in such cases, there may be localized areas with gray-black spots, which appear unclean. DM series die-cast aluminum alloys can be anodized in various colors. Please note that the information provided is general and specific practices may vary depending on the manufacturer and desired results.

Common Base Materials for Die-Cast Aluminum Anodizing

Die-cast aluminum ADC series: such as ADC6, ADC10, ADC12, etc.

Cast aluminum series: such as A356, A360, A380, etc.

DM series: such as DM3, DM6, etc.

Thickness of Die-Cast Aluminum Anodizing

The thickness of the anodized coating on die-cast aluminum is generally similar to that of regular anodizing, typically around 10μm. The range is typically between 5μm and 15μm.

Process Flow of Anodizing Die-Cast Aluminum Alloys

General Process Flow of Anodizing Die-Cast Aluminum

Aluminum workpiece → Hanging fixture → Degreasing → Water rinse → Alkaline etching → Water rinse → Polishing → Water rinse → Anodizing → Water rinse → Deionized water rinse → Dyeing or Electrolytic coloring → Water rinse → Deionized water rinse → Sealing → Water rinse → Unhanging fixture → Air blow drying → Oven drying → Quality inspection → Packaging → Shipment.

Note 1

Various colors in anodizing can be achieved through dyeing and electrolytic coloring. Unless otherwise specified, dyeing is the common method used. Compared to dyeing, electrolytic coloring provides more resistant colors, durable, and withstand high temperatures (up to 400 degrees Celsius). Standard anodizing may experience color fading at such high temperatures.

Note 2

The entire process of standard anodizing typically takes around 20 minutes to complete (additional time is required for achieving higher thicknesses of the anodized layer). However, black anodizing can take over 2 or even 3 hours to complete, making the cost of black anodizing higher than that of standard anodizing.

Note 3

Common pre-treatment processes for standard anodizing include sandblasting or wire brushing. If the surface of the workpiece does not require a high degree of smoothness, sandblasting can effectively enhance the adhesion between the anodized coating and the workpiece, making it more durable and wear-resistant. Quartz sand is commonly used for sandblasting and can be done either manually or automatically (some anodizing facilities may need to outsource sandblasting due to environmental regulations). The sandblasting grits available include 50 mesh, 80 mesh, 100 mesh, 120 mesh, 150 mesh, 180 mesh, 200 mesh, 220 mesh, and so on.

Display of Equipment for Anodizing Die-Cast Aluminum

Exhibition of Inspection Equipment for Anodizing Die-Cast Aluminum

Anodized Die-Cast Aluminum Sample Cases

Camouflage Anodizing

Camouflage Anodizing Process Overview

Camouflage anodizing, also known as pattern anodizing, is essentially achieved by multiple anodizing processes. Based on the anodizing coloring, different colors are added through multiple anodizing processes such as first anodizing, second anodizing, third anodizing, etc. to create a dazzling effect.

It is said that there is another implementation method, which is to use the masking spraying/dripping method on the basis of anodizing coloring to create a disorderly camouflage pattern of dual or multiple colors on the surface of the workpiece through color adjustment. However, this method is too complicated and has been discontinued.

Camouflage anodizing of aluminum parts is now widely used in the electronic industry, such as electronic cigarettes, fidget spinners, beauty pens, and other fields.

Camouflage Anodizing Process Flow

Polishing/Sandblasting/Brushing → Degreasing → Anodizing 1 → Sealing → Drying → Anodizing 2 → Sealing → Drying → Anodizing 3 → Sealing → Drying

Camouflage anodizing changes the surface appearance of metal by altering its surface morphology and structure, forming a layer of oxide film on the metal surface, and creating a unique camouflage effect. The process of camouflage anodizing mainly involves the following steps

Cleaning: use a cleaning agent to remove impurities from the metal surface to ensure that the surface is free of contaminants.
Acid washing: immerse the metal in an appropriate acid solution to corrode the metal surface and prepare it for surface oxidation.
Heat treatment: place the metal in a high-temperature environment to form a layer of oxide film on the surface, creating camouflage.
Polishing: polish the surface of the oxide film to make it smooth and shiny, achieving the camouflage effect.
Protection: apply a coating to the surface of the oxide film to increase its corrosion resistance and wear resistance and extend its service life.

Camouflage anodizing production equipment display.

Currently, there are stable and long-term cooperative manufacturers of camouflage anodizing that can meet customers’ requirements.

Camouflage Anodizing Testing Equipment Display

The display of inspection equipment for camouflage anodizing includes oxide film thickness gauge, colorimeter, gloss meter, roughness meter, pencil hardness tester, UV tester, constant temperature, and humidity machine, high and low-temperature tester, salt spray machine, vibration, and wear resistance tester, etc.

Sample Cases of Camouflage Anodizing

Here are some sample cases of camouflage anodizing

Camouflage anodized aluminum electronic cigarette

The surface of the electronic cigarette is treated with camouflage anodizing, which enhances the product’s visual appeal and makes it more attractive to customers.

Camouflage anodized aluminum spinner

The surface of the spinner is treated with camouflage anodizing, which not only adds an aesthetic element but also provides an extra layer of protection against wear and tear.

Camouflage anodized aluminum pen

The surface of the pen is treated with camouflage anodizing, which makes it more durable and resistant to corrosion, as well as more visually appealing.

Camouflage anodized aluminum flashlight

The surface of the flashlight is treated with camouflage anodizing, which gives it a unique appearance and helps it stand out from other flashlights on the market.

Camouflage anodized aluminum rifle parts

Camouflage anodizing is often used on rifle parts to enhance their appearance and provide additional protection against rust and corrosion.

Color Anodizing

Brief Introduction to Color Anodizing Process

Color anodizing refers to a process where the oxide film on the surface of a workpiece is dyed or electrolytically colored after ordinary anodizing, allowing the oxide film to present various desired colors.

Color anodizing is a process that uses electrolysis to produce a decorative and protective oxide coating on the surface of metal substrates, typically aluminum. The anodizing process involves immersing the metal substrate in an electrolyte solution and passing an electric current through it, which causes the surface to oxidize and form a layer of aluminum oxide. The thickness of the oxide layer can be controlled through the voltage and duration of the process, which is important for achieving consistent coloration. In the case of color anodizing, dyes or pigments are added to the electrolyte solution to impart a desired color to the oxide layer. The type and concentration of the dye or pigment will affect the resulting color, and multiple colors can be achieved by either masking or patterning the metal substrate prior to anodizing. Once the desired color is achieved, the oxide layer is sealed to improve its corrosion resistance and durability.

The anodizing of aluminum products can usually be divided into three types: sulfuric acid anodizing, chromic acid anodizing, and oxalic acid anodizing. If not specifically stated, it usually refers to sulfuric acid anodizing.

Common Substrates for Color Anodizing

Aluminum and aluminum alloys: Common ones include 5052, 6061, 6063, etc.
Die-cast aluminum alloys: Usually, when die-casting aluminum alloys are anodized, only the natural color (gray) or black can be achieved. However, there are also a few anodizing plants that can achieve color anodizing on die-cast aluminum alloys.
Magnesium alloys: Mainly used for conductive oxidation/chemical oxidation, with colors such as white and yellow. Titanium alloys: Color anodizing of titanium alloys can achieve various colors, such as blue, yellow, green, gold, etc.

Thickness of Color Anodized Film：

The thickness of color anodized coating is usually around 10μm, ranging from 5-15μm.

The Function of Color Anodizing:

Protective: increase surface hardness (HV300) and enhance wear resistance and corrosion resistance;
Decorative: can create various colors and surface effects;
Insulating: the oxide film is non-conductive and can act as an insulator;
Can improve the adhesion between parts and organic coatings;
Can improve the adhesion between parts and inorganic coatings.

Different Colors of Color Anodizing

Color anodizing is mainly achieved through two processes: dyeing and electrolytic coloring (also known as secondary electrolytic film).

Dyeing involves adsorbing pigments into the gaps of the oxide film and achieving different colors through subsequent sealing treatment. Dyeing has the advantages of fast coloring, bright color, and simple operation. In addition, it is common for customers to provide a Pantone color code for specified colors, and some anodizing plants claim to be able to customize colors for customers. Although theoretically, anodizing plants can achieve any color, it is not cost-effective for both the plant and the customer to do so without a large volume of goods. If custom color matching is necessary, the starting price for the entire process is around 500USD.

Currently, anodizing plants can meet more than 99% of users’ demands for personalized colors through color matching. Therefore, the best way to achieve color anodizing that is fast, good, and cheap is to find an anodizing plant that can achieve the desired colors.

Dyeing: Natural, white, black, bright silver, gray, matte white, matte black, bright black, red, purple, yellow, green, gold, rose gold, champagne gold…almost all colors can be done!

Electrolytic coloring: Based on the transparent oxide film generated in the first electrolysis, the secondary electrolysis film is generated in a solution containing a metal salt by using an alternating current. The weather resistance, light resistance, wear resistance, etc. of the oxide film generated by electrolytic coloring are much better than those of the dyeing film, but the obvious limitation of electrolytic coloring is that the color is monotonous. Currently, the most commonly used electrolytic coloring is black, and a few other colors such as antique copper, golden yellow, and jujube red can also be produced. However, the overall color and glossiness are far inferior to those of the dyeing film.

Process Flow of Color Anodizing

Anodizing process for color anodized aluminum:

Aluminum workpiece → hanging fixture → degreasing → water rinsing → alkaline etching → water rinsing → brightening → water rinsing → anodizing → water rinsing → deionized water rinsing → dyeing or electrolytic coloring → water rinsing → deionized water rinsing → sealing → water rinsing → air blowing → drying → unloading fixture → quality inspection → packaging → shipping.

Display of color anodizing production equipment

Color anodizing production equipment includes a series of machines and tools used in the process of producing anodized aluminum with various colors. Some commonly used equipment includes:

Hanging Equipment

Used for hanging aluminum parts during the anodizing process.

Degreasing Machine

Used to remove oil, grease, and other contaminants from the surface of aluminum parts.

Acid Etching Tank

Used to etch the surface of aluminum parts with acid to prepare them for anodizing.

Anodizing Tank

Used for the anodizing process, where a current is passed through the aluminum part and an electrolytic solution to form an oxide layer on the surface of the aluminum.

Quality Inspection Equipment

Used for measuring and testing the thickness, color, gloss, roughness, and other properties of the anodized aluminum, including an oxide film thickness gauge, colorimeter, gloss meter, roughness tester, pencil hardness tester, UV tester, constant temperature and humidity chamber, high and low-temperature tester, salt spray tester, and vibration wear tester.

Dyeing Tank

Used to dye the oxide layer on the surface of the aluminum to achieve the desired color.

Sealing Tank

Used to seal the oxide layer to improve the durability and corrosion resistance of the anodized aluminum.

Auxiliary Equipment

Includes sandblasting machines, grinding machines, polishing machines, and other tools used in the pre-treatment and post-treatment processes of anodizing.

Color anodizing production line

Masion has stable cooperation with suppliers who are capable of providing various colors of anodizing to meet customer requirements, including fully automated production lines (for small parts), overhead crane plating lines (for large and heavy parts), and manual lines (for small parts). The maximum size of workpieces that can be accommodated is 5 meters in length, 1 meter in width, and 2 meters in height (or depth). Additionally, supporting facilities include an automatic sandblasting machine and 15 manual sandblasting machines. Masion also has access to outsourced resources for grinding, drawing, and high-gloss polishing.

Display of Production Equipment for Color Anodizing

The testing equipment for color anodizing mainly includes thickness gauge for oxide film, colorimeter, gloss meter, roughness tester, pencil hardness tester, UV tester, constant temperature and humidity chamber, high-low temperature tester, salt spray chamber, vibration and wear resistance tester, etc.

Sample Cases of Colored Anodizing

There are various types of sample cases for color anodizing, and some common ones are listed below:

Color Aluminum Anodizing doors and windows

Through color anodizing, various colors of oxide films can be added to the surface of aluminum alloy doors and windows, such as black, gold, silver, blue, green, etc., making the surface decorative and anti-corrosive.

Color Aluminum Anodizing automotive parts

Color anodizing can add color to the surface of automotive parts, such as gold, black, silver, gray, etc., while also increasing the surface hardness and wear resistance.

Color Aluminum Anodizing household items

Color anodizing can add various colors of oxide films to aluminum alloy household items, such as red, yellow, green, blue, etc., making their surface more decorative.

Color Aluminum Anodizing electronic product casings

Color anodizing can add color to the surface of aluminum alloy electronic product casings, such as black, silver, gold, etc., while also increasing their corrosion resistance and wear resistance.

Color Aluminum Anodizing aerospace components

Color anodizing can add color to the surface of aerospace components, such as gold, silver, black, etc., while also increasing their surface hardness and corrosion resistance.

Conductive oxidation(Anodizing)

Brief introduction of the conductive oxidation process

Conductive oxidation(anodizing), also known as chemical oxidation(anodizing), is typically carried out using chromic acid anodization. Therefore, some anodizing plants refer to it as chromating. Compared to regular anodization, conductive oxidation does not require the application of high voltage; instead, the workpiece is simply immersed in the oxidation solution, undergoing a purely chemical reaction.

After undergoing conductive oxidation, aluminum workpieces acquire certain corrosion resistance properties while retaining their surface conductivity. Additionally, conductive oxidation effectively prevents interference from electromagnetic signals.

Common Substrates for Color Anodizing

Thickness of Conductive Oxide Film

The thickness of the conductive oxide film is typically between 0.3-0.5 μm. Due to the requirement for a thin oxide film, conductive oxidation must be fast. Usually, the reaction takes only a short period of around ten to several tens of seconds before the object must be immediately removed from the oxidizing solution.

Common substrates for conductive oxidation

Aluminum and aluminum alloys are commonly known as 2A12, 5052, 6061, 6063, 7075, etc.

Magnesium alloys are usually subjected to anodizing treatment, which involves conducting oxidation.

Functions of Conductive Oxidation

1. Electrical Conductivity: It maintains good electrical conductivity.
2. Wear Resistance: It possesses certain wear-resistant properties. (However, it is advised not to test it by scratching with hard objects.)
3. Corrosion Resistance: It has a certain level of corrosion resistance.
4. Protection against Electromagnetic Signal Interference.

Colors of Conductive Oxide

For most oxide plants, conductive oxidation is usually done in the natural color (colorless). Only a few oxide plants are capable of performing colored conductive oxidation (rainbow, tan, gold). Conductive oxide can be categorized into silver-white conductive oxide and colored conductive oxide. The latter can further be divided into tan, rainbow, and gold conductive oxide.

Colorless transparent oxide film, with a thin film thickness of approximately 0.3-0.5 μm, exhibits good conductivity. It is primarily used for deformed aluminum electrical components.
With a film thickness of around 0.5 μm, it ranges from colorless to rainbow or deep brown. It has good corrosion resistance and fewer pores. It is applied to larger components or assemblies unsuitable for anodizing.
The oxide film is gold and rainbow in color, with better corrosion resistance. It is suitable for localized oxidation of aluminum alloy welding components.
The oxide film is rainbow-colored, thin, and exhibits better conductivity than the formula mentioned in No. 2. It is suitable for components that require certain conductivity.
After conductive oxidation, the oxide film needs to undergo post-treatment filling. The post-treatment formula is 30-50 g/L K2Cr2O7 (or Na2Cr2O7) (CP grade) at 90-95°C for 5-10 minutes. This is commonly used as an underlying layer for spray painting or electrophoretic coating processes.

Conductive Oxidation Process Flow

General Process Flow of Conductive Oxidation

Prepare the aluminum workpiece

Select the aluminum workpiece for conductive oxidation.

Mounting on fixtures

Secure the aluminum workpiece on fixtures for subsequent processing steps.

Degreasing/Deoiling

Clean the surface of the aluminum workpiece using suitable degreasing agents or deoiling agents to remove impurities and oils.

Water rinse

Thoroughly rinse the aluminum workpiece with clean water to ensure a clean surface.

Alkaline etching

Immerse the aluminum workpiece in an alkaline solution to remove surface oxide layers and contaminants through etching.

Water rinse

Rinse the aluminum workpiece again with clean water to remove any residues from the alkaline solution.

Brightening

Polish or mechanically treat the aluminum workpiece to achieve a smoother surface.

Water rinse

Rinse the aluminum workpiece again with clean water to ensure no residues remain on the surface.

Oxidation

Place the aluminum workpiece in an oxidation tank and perform oxidation treatment using appropriate oxidants and electric current at specific time and temperature. The oxidant is typically a solution containing sulfuric acid.

Continuous water rinse

After removing the aluminum workpiece from the oxidation tank, perform thorough rinsing with flowing water to remove oxidants and other residues.

Hot water rinse

Place the aluminum workpiece in hot water and perform high-temperature rinsing to further clean the surface.

Hot air blow dry

Use a hot air blower or oven to dry the aluminum workpiece with hot air, ensuring complete surface drying.

Baking and drying at 40 degrees Celsius (Aging treatment):

Place the dried aluminum workpiece in a drying chamber or oven and bake it at 40 degrees Celsius for a specific period to enhance the performance of the oxide film.

Unmounting fixtures

Retrieve the processed aluminum workpiece from the drying chamber or oven and remove it from the fixtures.

Quality inspection

Conduct quality inspection on the aluminum workpiece after conductive oxidation, including visual inspection and performance testing, to ensure compliance with specified requirements.

Packaging

Properly package the qualified aluminum workpiece to prevent damage and contamination.

Shipment

Safely transport the packaged aluminum workpiece to the designated destination.

Note 1

Since the conductive oxide film is colorless and transparent, it is difficult to judge the formation level of the film during the operation. Therefore, the process time specified in the procedure should be followed. If the solution temperature is below room temperature, the operation time should be extended to around 60 seconds, and if the solution temperature exceeds room temperature, it is appropriate to use 15-20 seconds.

Note 2

In conductive oxidation, poor adhesion of the oxide film may occur due to the following reasons: 1) excessively thick oxide film (caused by prolonged oxidation time), 2) high concentration of the oxidation solution, 3) excessive temperature of the oxidation solution, 4) lack of aging treatment for the oxide film.

Note 3

After conductive oxidation, the conductivity of the workpiece may be poor, mainly due to the excessive thickness of the oxide film, which is caused by prolonged oxidation time.

Conductive Oxidation Production Equipment Showcase

Conductive Oxidation Testing Equipment Showcase

Conductive Oxidation Sample Cases

Electrolytic Coloring of Anodized Aluminum

Brief Introduction tothe process of coloring aluminum electrolytic.

Electrolytic coloring of aluminumrefers to the process of achieving desired colors on the surface of the workpiece by electrolytic coloring on the basis of anodizing (in reality, only a few colors can be achieved).

The principle of aluminum electrolytic coloring involves the use of a physical method where, in the presence of an electric current, metal ions are reduced and deposited as colloidal particles in the pores of the oxide film. It is based on the transparent oxide film formed during the initial electrolysis and involves secondary electrolysis using alternating current in a solution containing metal salts to generate a secondary electrolytic film. The oxide film produced by aluminum electrolytic coloring exhibits improved weather resistance, lightfastness, and abrasion resistance compared to dyed films. However, aluminum electrolytic coloring has a noticeable limitation, which is the monotonous color range. Currently, the most commonly used color achieved through electrolytic coloring is black. A few other colors such as antique bronze, golden yellow, and dark red can also be achieved, but the overall color and glossiness are far inferior to dyed films.

The process flow of Aluminum electrolytic coloring

Aluminum Electrolytic Coloring Process:

Aluminum Electrolytic Coloring Production Equipment Display

Aluminum Electrolytic Coloring Inspection Equipment Display

Aluminum Electrolytic Coloring Sample Cases

Exposure Developing Anodized Oxidation

Brief introduction to Exposure developing anodized oxidation

Exposure development anodizing, often used to protect logos on workpieces, is commonly combined with two-color anodizing processes. The two most common methods for exposure development and two-color oxidation treatment are:

Ink protection with two dyeing steps: After polishing the workpiece, the logo area is protected with ink during exposure development. Then, sandblasting is performed, followed by the first round of anodizing, dyeing, and sealing. The logo protection ink is cleaned, and the second round of oxidation and dyeing is carried out (if the logo area requires color), followed by sealing. Two rounds of anodizing and dyeing: After the first round of anodizing, dyeing, and sealing, the oxide and dye film layer is removed through CNC machining, and then the second round of anodizing and dyeing is performed to achieve a two-color effect. Currently, the first method is commonly used.

Exposure development anodizing process flow

For the second round of anodizing process:

Exhibition of exposure development anodizing production equipment

Detection equipment display for exposure development anodizing.

Exposure development anodizing detection equipment display includes: oxide film thickness gauge, colorimeter, gloss meter, roughness meter, pencil hardness tester, UV tester, constant temperature and humidity chamber, high and low-temperature tester, salt spray chamber, and vibration wear resistance tester.

Exposure development anodizing sample cases.

Hard Anodizing.

Brief Introduction to Hard Anodizing Process

Hard Anodizing, also known as Hardcoat Anodizing, is a type of anodizing process that has higher requirements for the wear resistance of the oxide film on the workpiece. It can generally be categorized into the following methods:

Sulfuric Acid Hard Anodizing: This method uses sulfuric acid as the electrolyte to produce a hard and durable oxide film on the surface of the workpiece. It is the most commonly used and referred to method when talking about Hard Anodizing unless otherwise specified. Oxalic Acid Hard Anodizing: In this method, oxalic acid is used as the electrolyte to achieve a hard anodized coating with enhanced wear resistance. Mixed Acid Hard Anodizing: This method involves the use of a mixture of acids, such as sulfuric acid and oxalic acid, to achieve the desired hardness and wear resistance of the anodized coating.

These different methods of Hard Anodizing are employed based on specific requirements and considerations for the workpiece and its intended application. However, unless otherwise specified, the term “Hard Anodizing” typically refers to the sulfuric acid hard anodizing method.

Common Base Materials for Hard Anodizing:

Aluminum and aluminum alloys, such as 2A12, 5052, 6061, 6063, and 7075, are commonly used. Additionally, cast aluminum alloys like ADC10, ADC12, A356, and A380 are also frequently subjected to hard anodizing treatment.

For deformable aluminum alloys with a copper content greater than 5% or a silicon content greater than 8%, as well as high-silicon die-cast aluminum alloys, special measures need to be taken during hard anodizing. For example, to prevent burn damage to aluminum alloys during the anodizing process, an electrolyte solution containing 385 g/L sulfuric acid and 15 g/L oxalic acid can be used, and the current density should be increased to 2.5 A/dm² or higher for 2XXX series aluminum alloys.

Thickness of Hard Anodized Coating:

The thickness of hard anodized coatings typically ranges from 25 μm to 150 μm, with most coatings falling between 50 μm and 80 μm. Additionally, there are claims of achieving super-thick coatings of 200 μm or more, but I cannot confirm this as I have not encountered such cases. Hard anodized coatings with a thickness of less than 25 μm are commonly used for components used in applications such as gears and helical springs. Coatings with a thickness of around 50 μm are used for wear resistance or insulation purposes. Only under special environmental conditions such as high temperature, high humidity, and high pressure, coatings of 125 μm or more may be required. (I have encountered products used in marine environments and medical equipment exposed to high-temperature plasma radiation, which had very stringent requirements. The process from product validation to mass production was quite challenging, and it is a daunting task to look back on it now!)

It should also be noted that since the hard anodized coating is a two-sided growth process, achieving a 100 μm coating thickness actually means adding 50 μm to each side.

Furthermore, it should be noted that the thicker the hard anodized coating, the lower the microhardness of the outer layer (the oxide layer becomes more brittle), and the roughness of the coating surface increases.

Functions of Hard Anodizing:

High wear resistance: The surface hardness can reach 500 HV.

Excellent thermal insulation coating: Melting point is 2050°C, with poor thermal conductivity.

Good insulation properties: High resistance, with breakdown voltage of up to 2000V.

Strong adhesion of the coating: Approximately 50% of the generated oxide film penetrates into the aluminum alloy, and the remaining 50% adheres to the surface of the aluminum alloy.

Extremely high corrosion resistance: It exhibits excellent corrosion resistance in industrial and marine climates.

Colors of Hard Anodized Coatings:

The colors typically achieved on the surface of hard anodized coatings are natural (unaltered) and black. In the case of natural hard anodizing, a range of colors can be achieved, including shades of gray, dark gray, brown/grayish-brown, and brown. The color of the hard anodized coating can vary depending on the different base materials used. Additionally, as the thickness of the coating increases, the color of the oxide layer becomes darker.

Conductive Oxidation Process Flow

Hard Anodizing Process Flow

Aluminum Workpiece
Hanging Fixture
Degreasing/Chemical Oil Removal
Cold Water Rinse
Alkali Etching
Water Rinse
Polishing/Electrolytic Polishing
Water Rinse
Hard Anodizing
Hot Water Rinse
Deionized Water Rinse
Dyeing or Electrolytic Coloring
Water Rinse
Deionized Water Rinse
Sealing
Cold Water Rinse
Remove Hanging Fixture
Air Blow
Drying
Quality Inspection
Lubrication
Packaging
Shipping;

Note 3

A common issue that arises during the production of the darkest black hard anodizing is the presence of water spots. This is caused by residual moisture in some through-holes or blind holes of the workpiece that was not completely blown dry (usually due to impatience and inadequate drying). Therefore, when producing the darkest black anodizing, it is important to ensure that the moisture is completely removed by thorough blowing and, if possible, additional drying in an oven. Once water spots remain, they cannot be easily removed after some time, resulting in the need for rework, which may affect the dimensional tolerances of the workpiece and should be avoided if possible.

Note 1

Hard anodizing typically requires a process time of over 3 hours due to lower concentrations and temperatures of the electrolyte compared to conventional anodizing (conventional anodizing solution is typically around 20°C, while hard anodizing is around 5°C). This results in a slower production rate of the oxide layer, and the thicker the layer, the longer the required time.

Note 2

Unlike conventional anodizing, hard anodizing requires an additional step at the end of the process, which is lubrication. This step creates a smooth surface appearance and a delicate touch, but there is no oily sensation on the workpiece.

Display of Equipment for Hard Anodizing Production

The hard anodizing production line is showcased with the capability to process workpieces of up to 4.5 meters in length, 1 meter in width, and 2 meters in height (depth).

In addition, the supporting facilities include an automatic sandblasting machine and 15 manual sandblasting machines. There are also resources available for grinding, brushing, and high-polishing processes through outsourcing. The daily average production capacity exceeds one million units, ensuring abundant production capacity.

Display of Equipment for Hard Anodizing Inspection

Portable Coating Thickness Gauge: A handheld coating thickness gauge is used to measure the thickness of the anodized layer. It provides quick and non-destructive measurements, allowing for on-site inspection and verification of coating thickness.
X-ray Coating Thickness Gauge: An X-ray coating thickness gauge utilizes X-ray fluorescence (XRF) technology to measure the thickness of the anodized layer. It offers high precision and accuracy, particularly for thicker coatings.
Salt Spray Testing Machine: A salt spray testing machine, also known as a salt fog chamber, is employed to simulate corrosive environments. It exposes the anodized parts to a saltwater mist, assessing their resistance to corrosion over a specified period.
Hardness Tester: A hardness tester measures the hardness of the anodized surface. Various methods, such as Rockwell or Vickers hardness testing, can be utilized to evaluate the coating’s hardness and mechanical properties.

Sample Cases of Hard Anodizing

Anodizing Large Parts

Brief Introduction to the Process of Anodizing Large Parts

For large partsof color anodizing, workpieces with a length of over 4000mm or a height of over 1500mm can be processed with color anodizing. The maximum size for anodizing is a workpiece with a length of 5000mm, a width of 800mm, and a height of up to 2000mm. Within this size range, sandblasted anodizing, hard anodizing, brushed anodizing, polished anodizing, and color anodizing (such as bright silver, black, red, gold, rose gold, yellow, etc.) can be performed.

The functions of anodizing large parts are as follows:

Protective: It increases surface hardness (HV300) and improves wear resistance. Decorative: It can create various surface colors and effects. Insulation: The anodized film is non-conductive and can provide insulation. Enhanced adhesion to organic coatings. Improved adhesion to inorganic overlay coatings.

The common base materials for anodizing large parts:

Aluminum and Aluminum Alloys: Common types include 5052, 6061, 6063, etc.

Film thickness for anodizing large parts:

The film thickness of color anodization is typically around 10μm, with a range between 5-15μm.

Colors for anodizing large parts:

In domestic color anodizing processes, coloring and electrolytic coloring (also known as secondary electrolytic film) are the two main methods used. Currently, oxide factories can meet over 99% of customers’ demands for personalized colors through coloring techniques. Therefore, the best way to achieve fast, good, and cost-effective color anodizing is to find an oxide factory capable of producing the desired colors. Coloring: Original color, white, black, bright silver, gray, matte white, matte black, glossy black, red, purple, yellow, green, gold, rose gold, and many more. Virtually all colors can be achieved. Electrolytic coloring: It is based on the transparent oxide film formed during the first electrolysis process. In a solution containing metal salts, a second electrolysis process is conducted using alternating current to create a secondary electrolytic film. The oxide film generated through electrolytic coloring exhibits better weather resistance, light resistance, and wear resistance compared to the coloring film. However, electrolytic coloring has the limitation of producing monotonous colors. Currently, the most commonly used color for electrolytic coloring is black. Additionally, a few other colors such as antique bronze, golden yellow, and maroon can be achieved, although the overall color glossiness is not as good as the coloring film.

Process Flow for Anodizing Large Parts.

The process flow of color anodization:

Display of Production Equipment for Anodizing Large Parts

Display of Inspection Equipment for Anodizing Large Parts.

Sample Cases of Anodizing Large Parts.

Microarc Oxidation

Brief Introduction to Microarc Oxidation Process

Microarc Oxidation (MAO), also known as Plasma Electrolytic Oxidation (PEO), refers to a method of forming high-quality ceramic-like coatings on the surfaces of materials such as aluminum, titanium, magnesium, and their alloys by using arc discharge to enhance and activate the reactions occurring on the anode during conventional anodizing.

Workpieces treated with micro-arc oxidation exhibit significantly improved corrosion resistance and wear resistance compared to traditional anodized coatings, making them widely used in marine vessels, aerospace components, and other applications.

Common Substrates for Microarc Oxidation:

Aluminum and aluminum alloys: Micro arc oxidation has relatively low requirements for aluminum materials. Whether it is copper-containing or silicon-containing aluminum alloys that are difficult to anodize, as long as the valve metal proportion exceeds 40%, they can be used for micro arc oxidation and achieve desirable coatings. Additionally, common substrates for micro-arc oxidation include magnesium alloys and titanium alloys. In addition, valve metals such as zirconium, niobium, and tantalum can also undergo micro-arc oxidation.

Thickness of Microarc Oxidation Coatings:

The thickness of micro-arc oxidation coatings is slightly greater than that of conventional anodizing, typically ranging from 20 to 30 μm. Some manufacturers claim to achieve coatings with thicknesses of 200 to 300 μm, but this has not been verified by the speaker.

Microarc Oxidation Colors:

Common colors of micro-arc oxidation coatings are earthy gray/brown and black. Some manufacturers can also achieve coffee-colored micro-arc oxidation coatings in addition to the aforementioned colors.

Effects of Microarc Oxidation:

Significantly increased surface hardness of materials, with microhardness ranging from 1000 to 2000 HV and up to 3000 HV, comparable to hard alloys and much higher than the hardness of high-carbon steel, high-alloy steel, and high-speed tool steel after heat treatment.
Good wear resistance.
Excellent heat resistance and corrosion resistance. This fundamentally overcomes the shortcomings of aluminum, magnesium, and titanium alloy materials and thus has broad application prospects.
Good insulation properties, with insulation resistance up to 100 MΩ.
Environmentally friendly electrolyte solution that meets environmental emission requirements.
Stable and reliable process with simple equipment.
The reaction takes place at room temperature, making it convenient to operate and easy to master.
The ceramic coating grows in situ on the substrate, ensuring strong adhesion and a uniform and dense ceramic layer.

Microarc Oxidation (MAO) Process Flow

Note 1

Polishing treatment is generally not required for the surface condition of the workpiece before micro-arc oxidation. The process can smooth and restore rough surfaces. However, it may increase the roughness of low-roughness (smooth) surfaces.

Note 2

The typical duration for micro-arc oxidation is controlled between 10 to 60 minutes. Longer oxidation times result in denser coatings but may also increase roughness.

Note 3

Micro arc oxidation differs from conventional anodizing in terms of temperature requirements. The temperature range is generally 10-90 degrees Celsius. Higher temperatures lead to faster film formation but also increase roughness. High temperatures can generate water vapor. It is recommended to maintain a temperature range of 20-60 degrees Celsius. Since micro-arc oxidation releases thermal energy, the liquid temperature rises rapidly. Therefore, the micro-arc oxidation process should be equipped with a large-capacity heat exchange and cooling system to control the bath temperature.

Microarc Oxidation (MAO) Production Equipment Showcase

The micro-arc oxidation production line showcases the capability to perform micro-arc oxidation on materials such as aluminum alloys, magnesium alloys, titanium alloys, etc., producing gray, brown, black, and coffee-colored coatings. Microarc Oxidation Production Line Showcase

The micro-arc oxidation production line showcases the capability to perform micro-arc oxidation on materials such as aluminum alloys, magnesium alloys, titanium alloys, etc., producing gray, brown, black, and coffee-colored coatings.

Microarc Oxidation Testing Equipment Showcase

The showcase of microarc oxidation testing equipment includes the characterization of the protective coatings’ performance. It mainly involves the characterization of thickness, hardness, morphology, phase composition, and surface roughness.

To measure the thickness of the oxide ceramic coatings, a German handheld thickness gauge (such as HUATEC) is used for precise thickness characterization. For the measurement of surface microhardness, a microhardness tester is employed to assess the hardness of the coating surface.

The surface, cross-section morphology, and microstructure of the micro-arc oxidation ceramic coatings are examined using an environmental scanning electron microscope (SEM). This technique allows for detailed inspection and characterization of the coating’s surface features and microstructure.

These testing equipment and techniques provide valuable information regarding the thickness, hardness, morphology, composition, and surface roughness of micro-arc oxidation coatings. They help ensure the quality and performance of the coatings and assist in meeting the required specifications for different applications.

Microarc Oxidation Sample Cases

Here are some sample cases of micro-arc oxidation:
Aluminum Alloy: A6061-T6

Color: Gray
Surface Finish: Smooth
The thickness of Ceramic Coating: 25 μm
Performance: Enhanced hardness, wear resistance, and corrosion resistance
Magnesium Alloy: AZ91D

Color: Brown
Surface Finish: Textured
The thickness of Ceramic Coating: 30 μm
Performance: Improved surface hardness, wear resistance, and anti-corrosion properties
Titanium Alloy: Ti6Al4V
Color: Black

Surface Finish: Matte
The thickness of Ceramic Coating: 35 μm
Performance: Increased surface hardness, wear resistance, and high-temperature resistance
Aluminum Alloy: AA7075

Color: Coffee
Surface Finish: Fine grain
The thickness of Ceramic Coating: 28 μm
Performance: Enhanced hardness, wear resistance, and corrosion resistance

Precision Anodizing

Brief Introduction of the precision anodizing process

Precision anodizing refers to the anodizing process performed on workpieces with strict dimensional tolerances. During anodizing, it is necessary to carefully control the anodic oxide film’s thickness to avoid problems during the assembly process caused by excessive or insufficient oxide film thickness.

When conducting precision anodizing, it is essential to consider the allowance dimensions of the workpiece. Additionally, careful consideration should be given to the impact of rework and de-anodizing on the dimensional integrity of the workpiece.

Precision anodizing process.

Precision anodizing follows the same process as regular anodizing and hard anodizing. The general process is as follows:

Precision anodizing production equipment showcase.

Precision anodizing production equipment display.

Precision anodizing inspection equipment display. The inspection equipment for precision anodizing includes an oxide film thickness gauge, colorimeter, gloss meter, roughness meter, pencil hardness tester, UV tester, constant temperature and humidity chamber, high-low temperature tester, salt spray chamber, vibration, and wear resistance tester, etc.

Precision anodizing sample cases.

Titanium anodizing

Brief Introduction to the Titanium Anodizing Process

The anodizing process of titanium and titanium alloys utilizes titanium as the anode and other metals such as stainless steel as the cathode, with the assistance of a certain electrolyte. Through electrochemical reactions, the titanium alloy surface undergoes oxidation to form an oxide film. This oxide film exhibits significant reflection and refraction of light and displays different colors depending on its thickness. It also provides protection, making it an ideal decorative and wear-resistant layer. As a result, it is widely used in fields such as construction, aerospace, and medicine.

What colors can be achieved through titanium anodizing?

Titanium anodizing process

Degreasing

Degreasing is performed to remove residual oils on the surface of titanium from the rolling process. Oil residues have poor water permeability and can lead to uneven coloring during acid etching of titanium surfaces.

Initial acid etching

Initial acid etching is carried out to create a pearlescent pattern on the surface of titanium and its alloys. Using a 5% weight concentration of hydrofluoric acid for acid etching promotes the formation of the pearlescent pattern.

Secondary acid etching

Secondary acid etching is performed to remove the powdery residue formed on the surface during the initial acid etching. Additionally, to ensure uniform acid etching, it is necessary to stabilize titanium ions by using a mixture of hydrofluoric acid and hydrogen peroxide solution after the initial removal of surface impurities with hydrofluoric acid.

Anodizing

Anodizing is performed by using a 1% weight concentration of phosphoric acid as the electrolyte. Aluminum plates are used as cathodes, while pre-treated titanium plates are used as anodes for constant voltage treatment. As the voltage increases, the thickness of the oxide film on the titanium surface increases, resulting in various color variations.

Sealing

To improve the corrosion resistance, pollution resistance, and wear resistance of the anodized oxide film, titanium alloy,is subjected to sealing treatment using hot water, steam, and solutions containing inorganic salts and organic compounds after anodizing and coloring.

Drying

After sealing, the workpiece is dried by gently wiping off the water with a clean cloth, allowing it to air dry naturally.

Exhibition of Production Equipment for Titanium anodizing

Titanium Anodizing Detection Equipment Show.

The detection equipment for titanium alloy color anodizing mainly includes an oxide film thickness gauge, colorimeter, gloss meter, roughness meter, pencil hardness tester, UV tester, constant temperature, and humidity chamber, high and low temperature tester, salt spray machine, vibration wear tester, etc.

Titanium anodized sample case

Two-tone anodizing/Secondary anodizing

Introduction to Two-Tone Anodizing Process

Two-tone anodizing is a surface treatment process that involves secondary anodizing and dyeing/electrolytic coloring of a workpiece to achieve two different colors. It is a popular technique used to enhance the aesthetic appeal and visual contrast of metal surfaces.

The process typically involves two main steps. Firstly, the workpiece undergoes the primary anodizing process, where a protective oxide layer is formed on its surface through an electrolytic reaction. This primary anodizing step provides a base layer of uniform and corrosion-resistant oxide.

After the primary anodizing, the workpiece is prepared for the secondary anodizing and coloring step. There are two common methods used to achieve the two-tone effect.

The first method involves mechanical polishing. Areas of the workpiece that require a different color are carefully polished using CNC or other computer-controlled tools to remove the primary oxide layer. This creates a clean surface for the subsequent anodizing and coloring process. The polished areas are then subjected to a secondary anodizing step, where a new oxide layer is formed. This second oxide layer is porous and provides a suitable base for dyeing or electrolytic coloring. Different dyes or coloring agents are applied to the porous oxide, resulting in the desired two-tone appearance.

The second method involves masking. Specific areas of the workpiece that need a different color are masked or covered before the primary anodizing process. The masked areas remain unoxidized during the primary anodizing step. Afterward, the masking is removed, and the entire workpiece undergoes a secondary anodizing process. The previously masked areas now develop a new oxide layer during the secondary anodizing. These areas are then dyed or colored separately, resulting in the desired two-tone effect.

It is important to note that achieving a consistent texture and surface finish between the two colors can be challenging, especially on complex 3D structures. Additionally, the masking method may result in jagged edges or serrations along the masked boundaries, which can affect the overall appearance. Two-tone anodizing finds applications in various industries, including architecture, automotive, electronics, and fashion, where both functionality and aesthetics are essential.

Two-Tone Anodizing Process Flow

Aluminum Workpiece
Hanging Fixture
Degreasing
Rinse
Alkaline Etching
Rinse
Brightening
Rinse
Primary Anodizing
Rinse
Deionized Water Rinse
Primary Dyeing or Electrolytic Coloring
Rinse
Deionized Water Rinse
Sealing
Masking
Curing
Deoxidation
Chemical Polishing
Secondary Anodizing
Rinse
Secondary Dyeing or Electrolytic Coloring
Rinse
Sealing
Ink Removal
Rinse
Blow Dry
Drying Oven
Unhanging Fixture
Blow Dry
Drying Oven
Quality Inspection
Packaging
Shipping.

Display of Two-Tone Anodizing Production Equipment

Two-Tone Anodizing Production Line

The inspection equipment used for two-tone anodizing primarily includes:

Oxide layer thickness gauge

Used to measure the thickness of the anodized layer. This helps ensure that the desired thickness is achieved and meets the specified requirements.

Colorimeter

Used for precise color measurement and evaluation of the anodized surfaces. This device ensures color consistency and adherence to color specifications.

Gloss meter

Measures the gloss or shine of the anodized surfaces, providing quantitative data for surface quality assessment.

Roughness tester

Measures the surface roughness of the anodized workpieces. This equipment helps evaluate the smoothness and texture of the surfaces.

Pencil hardness tester

Determines the hardness of the anodized coating by conducting a pencil scratch test. It provides an indication of the coating’s resistance to scratching or abrasion.

UV tester

Evaluates the resistance of the anodized coating to UV radiation, simulating the effects of prolonged exposure to sunlight.

Constant temperature and humidity chamber

Maintains a controlled environment of stable temperature and humidity for conducting tests that assess the anodized coating’s performance under specific conditions.

High-low temperature tester

Subject the anodized workpieces to extreme temperature variations to evaluate the coating’s resistance to thermal stress.

Salt spray chamber

Simulates a corrosive environment by exposing the anodized workpieces to a salt mist or fog. This test assesses the corrosion resistance of the anodized coating.

Vibration and wear resistance tester

Evaluates the resistance of the anodized surfaces to vibration and wear, simulating real-world conditions and ensuring their durability.

These inspection devices and equipment play a vital role in verifying the quality, durability, and performance of the two-tone anodized workpieces.