The production of aluminum profiles follows a systematic process, beginning with the synthesis of aluminum with other alloying elements through casting to obtain aluminum ingots. These ingots serve as raw materials for producing aluminum billets, which are then used to manufacture extruded industrial aluminum profiles.
Processing Flow of Aluminum Profiles
Aluminum profile oxidation is a common surface treatment process, which is mainly used to improve the corrosion resistance, wear resistance and aesthetics of aluminum. The following is a common aluminum profile oxidation process flow.
First, the aluminum profile is cleaned. The purpose of cleaning is to remove oil, dust and impurities on the surface of the aluminum so that it can fully contact with the oxidizing liquid. The cleaning method can be chemical cleaning or mechanical cleaning. Chemical cleaning can use acid cleaning liquid or alkaline cleaning liquid, while mechanical cleaning can use sandblasting, polishing and other methods.
After cleaning, the aluminum profile needs to be deoxidized. The purpose of deoxidation is to remove the oxide film on the surface of the aluminum so that the oxidizing liquid can better contact the aluminum. Deoxidation can use hydrofluoric acid solution or nitric acid solution. During the deoxidation process, it is necessary to pay attention to controlling the concentration and temperature of the deoxidizing liquid to avoid excessive corrosion of the aluminum.
After the deoxidation treatment is completed, the aluminum profile needs to be pickled. The purpose of pickling is to remove the metal salts and organic matter remaining in the deoxidizing liquid, as well as oxides, silicates, etc. on the surface of the aluminum. Pickling can use sulfuric acid solution, hydrochloric acid solution or oxalic acid solution. During the pickling process, the concentration, temperature and time of the pickling solution need to be controlled to ensure a good cleaning effect on the aluminum.
After pickling, the aluminum profile needs to be oxidized. Oxidation is the core link of the aluminum profile oxidation process, which mainly forms a uniform and fine oxide film on the surface of the aluminum by electrolytic oxidation. The oxidizing solution is mainly composed of sulfuric acid, disulfuric acid, boric acid, etc. During the oxidation process, it is necessary to control the temperature, concentration, current density and oxidation time of the electrolyte to obtain the required oxide film thickness and performance.
After the oxidation treatment is completed, the aluminum profile needs to be sealed. The purpose of sealing is to improve the sealing and corrosion resistance of the oxide film. Sealing can be done by water sealing, heat sealing or anodic sealing. Water sealing is to immerse the aluminum in hot water so that the pores of the oxide film are filled with water molecules. Heat sealing is to heat the aluminum to a certain temperature so that a transition layer is formed on the surface of the oxide film to improve the sealing of the oxide film. Anodic sealing is to form a hard sealing layer on the surface of the oxide film by anodizing.
Finally, the aluminum profile is cleaned, dried and inspected. The purpose of cleaning is to remove the residues produced during the sealing process, and drying is to remove moisture and prevent corrosion. Inspection is to test the thickness, hardness, sealing and color of the oxide film to ensure that it meets the requirements.
In short, the aluminum profile oxidation process includes steps such as cleaning, deoxidation, pickling, oxidation, sealing, cleaning, drying and inspection. Through these processes, an aluminum oxide film with good quality and stable performance can be obtained, which improves the corrosion resistance, wear resistance and aesthetics of the aluminum.
The key steps involved in transforming aluminum billets into industrial aluminum profiles are as follows:
- Furnace Heating – The aluminum billets are heated in a furnace to prepare them for extrusion.
- Mold Design – Molds are designed according to product specifications, serving as shaping tools during the extrusion process.
- Extrusion Process – The heated aluminum billets are extruded using an extrusion press. Common 6063-T5 series profile extrusion presses typically range from 1,300 to 1,600 tons. For larger or higher-specification profiles, presses with higher tonnage are used based on production requirements.
- Profile Straightening – The extruded aluminum profiles are aligned and corrected to ensure proper shape and dimensions.
- Stretching – The profiles undergo a stretching process to enhance their mechanical properties.
- Aging Treatment – This is a critical step that determines the strength and hardness of the aluminum profiles.
- Anodizing – The profiles undergo anodization to improve corrosion resistance and surface durability.
- Sandblasting & Anodizing – A secondary surface treatment that refines the profile’s texture by eliminating extrusion lines, reducing surface micro-pores, and enhancing oxidation resistance.
This process ensures high-quality aluminum profiles with excellent strength, durability, and surface finish, suitable for various industrial applications.
Anodizing Process of Industrial Aluminum Profiles
Surface Treatment of Aluminum Profiles
Also known as surface pretreatment, this step involves using physical and chemical methods to remove contaminants from the aluminum surface. The goal is to expose the bare aluminum, ensuring a clean surface for the subsequent anodizing process.
Degreasing Process
The purpose of degreasing is to remove industrial lubricants, anti-corrosion oils, and other impurities adhering to the aluminum surface. This step ensures uniform alkaline etching, maintains the cleanliness of the etching bath, and improves the overall surface treatment quality.
Acid Etching Process
After degreasing, acid etching is performed to remove oxides formed from other metal elements and the naturally occurring oxide layer on the aluminum surface. Immediately after acid etching, the profiles must be rinsed with water at a controlled temperature of 50°C to prevent streak marks. This is followed by a flowing water rinse.
Since aluminum contains copper elements, its surface may appear dark after acid etching. To restore a bright silver finish, the profiles are soaked in a nitric acid solution for 3–5 minutes.
This anodizing process enhances the corrosion resistance, durability, and aesthetic appearance of industrial aluminum profiles, making them suitable for various applications.
Alkaline Etching Process
The alkaline etching process serves a similar purpose as acid etching. It removes residual substances and degraded layers from the aluminum surface formed during oxidation. Additionally, it eliminates surface defects such as scratches left from the extrusion process. Alkaline etching is a critical step in ensuring the overall surface quality of aluminum profiles.
Neutralization Process
The neutralization process removes insoluble alloy elements or impurities such as copper, manganese, iron, and silicon that remain on the aluminum surface after acid and alkaline etching. It also neutralizes residual alkaline solutions from the previous step.
Typically, a 30%-50% nitric acid solution is used for neutralization. For high-silicon aluminum alloys or cast alloys, a 1:3 volume ratio of nitric acid and hydrofluoric acid is applied. Silicon reacts with hydrofluoric acid to form flu silicic acid, allowing it to be removed from the aluminum surface.
Anodizing Treatment
Anodizing is performed by using an electrolyte solution as a medium and applying high-voltage discharge, forming a protective oxide layer on the aluminum surface. This process significantly enhances the corrosion resistance of the aluminum profile. The standard anodized layer thickness is 10-12μm, which improves oxidation resistance and enhances the appearance of the profile.
- Sulfuric Acid Anodizing:
- Electrolyte: 10-20% HSO
- Operating Temperature: 15-20°C
- Current Density: 1-2.5 A/dm²
- Electrolysis Time: 20-60 minutes (depending on required film thickness)
- Voltage: Typically, 15-20V, depending on electrolyte conductivity, temperature, and aluminum content
Impact of Process Parameters: The properties of the anodized film are significantly influenced by process parameters.
Sealing Treatment
After anodizing, the aluminum surface contains micro-pores, making it susceptible to oxidation and corrosion over time. Sealing treatment is performed to close these pores and improve durability.
Cold Sealing Process
This advanced sealing technique, originating from Europe, is commonly used for industrial aluminum profiles.
- Sulfuric Acid Anodizing Parameters:
- Electrolyte: 10-20% HSO
- Operating Temperature: 15-20°C
- Current Density: 1-2.5 A/dm²
- Electrolysis Time: 20-60 minutes (depending on required film thickness)
- Voltage: Typically 15-20V
The choice of sealing method and process parameters plays a crucial role in determining the final performance and longevity of the anodized aluminum profile.
This comprehensive anodizing process ensures that industrial aluminum profiles achieve superior durability, corrosion resistance, and a high-quality finish.
