Share with you: How is the alumina board made?

To understand the manufacturing process of alumina board, it is necessary to clarify its core definition: alumina board (commonly called "anodic alumina board" in industry) is not directly pressed with alumina powder, but a dense, wear-resistant and corrosion-resistant aluminum oxide (Al₂O₃) film is formed on the surface of pure aluminum board by electrochemical anodic oxidation technology, which is essentially a composite structure of "substrate+surface oxide film".

Its complete production process can be divided into three stages: substrate pretreatment, core anodizing and post-treatment, each of which directly affects the performance and appearance of the final product. The specific steps are as follows:

First stage: pretreatment of substrate-"laying the foundation" for oxide film.

The core goal of pretreatment is to remove the oil stain, oxide layer and impurities on the surface of aluminum plate, ensure the surface is smooth and create conditions for the subsequent uniform formation of oxide film, which mainly includes four steps:

Selection of base material: First-series pure aluminum plates (such as 1050 and 1060 models) with a purity of ≥99.5% are preferred for the "base material", which has low impurity content and even surface without spots after oxidation; If the strength is required, 3-series (Al-Mn alloy) or 5-series (Al-Mg alloy) aluminum plates will also be used, but the subsequent process parameters need to be adjusted to avoid alloying elements affecting the quality of the oxide film.

Cutting and cleaning: removing "dirt"

Firstly, according to the size of the finished product, the aluminum plate is cut into the required specifications with a shearing machine or a laser cutting machine;

Soak in alkaline degreasing agent (such as sodium hydroxide solution) (temperature 50-70℃, time 5-15min) to remove engine oil and dust attached to the surface of aluminum plate during processing and storage;

Finally, rinse with pure water to avoid the influence of residual lye on the subsequent steps.

Pickling and degreasing: When the aluminum plate with the "oxide layer" removed is exposed to air, it will naturally form a loose "primary oxide film" (the thickness is only a few nanometers, which has no protective effect). It is necessary to use dilute nitric acid or dilute sulfuric acid solution (concentration 10%-20%) for pickling to dissolve the primary oxide film, and at the same time further remove the residual oil, so that a fresh metal layer is exposed on the surface of the aluminum plate. Rinse with pure water again after pickling to prevent acid from corroding the substrate.

Polishing: improve the flatness, and select the polishing method according to the product appearance requirements;

If mirror effect is needed: mechanical polishing (cloth wheel polishing) or chemical polishing (phosphoric acid+sulfuric acid solution) is adopted to reduce the surface roughness of aluminum plate to Ra ≤ 0.2μ m;

If only matte or ordinary appearance is needed: polishing can be omitted, or only "electrolytic polishing" is done lightly to improve the surface uniformity.

Second, the second stage: core anodic oxidation-formation of "protective oxide film"

This is the key step in the production of alumina plate: through electrochemical reaction, the aluminum plate is used as an "anode" and electrified in a specific electrolyte, forcing the surface of the aluminum plate to oxidize to form a controllable and dense alumina film. It is divided into three core links:

1. Electrolyte configuration: determines the performance of oxide film.

There are two kinds of commonly used electrolytes, corresponding to different product requirements:

Electrolyte Type Composition (Core) Oxide Film Features Applicable Scenarios

Sulfuric acid type 15%-20% sulfuric acid solution oxide film is porous, strong in adsorption (easy to dye) and low in cost for decorative aluminum plates (such as home appliance panels and architectural decoration).

Oxalic acid type 5%-10% oxalic acid solution oxide film has high hardness, strong corrosion resistance and compact film layer (such as mechanical parts and high temperature resistant parts).

The electrolyte temperature should be strictly controlled (20-25℃ in sulfuric acid system and 40-50℃ in oxalic acid system). If the temperature is too high, the oxide film will dissolve too fast and the film will become thinner. If the temperature is too low, the reaction will be slow and the efficiency will be low.

2. Anodic oxidation electrification: "grow" oxide film

The pretreated aluminum plate is put into electrolyte, and the lead plate or stainless steel plate is used as cathode, and the DC power supply (voltage 12-18V, current density 1-2a/dm) is connected, and the following core reactions occur:

Anode (aluminum plate): aluminum atoms lose electrons and generate aluminum ions (Al-3e→ Al), which combine with OH in electrolyte to generate alumina (2Al³⁺+6OH⁻ → Al₂O₃+3H₂O), and gradually accumulate on the surface of aluminum plate to form an oxide film;

Cathode: H in the electrolyte gains electrons to generate hydrogen (2h+2e→ h ↑), and some sulfate ions participate in the reaction to maintain the stability of the electrolyte.

The power-on time is adjusted according to the required film thickness: the film thickness of the common decorative board is 5-10μm, and the power-on time is 20-30min; The film thickness of the high wear-resistant plate is 20-50μm, and it is electrified for 60-120min.

3. Sealing of oxide film: from "porous" to "dense"

Alumina film produced by anodic oxidation has a porous structure (pore size is about 10-100nm). Although it has a certain hardness, it is easy to absorb impurities and be corroded. It is necessary to plug the pores by "sealing treatment" to improve corrosion resistance and surface smoothness. There are two common sealing methods:

Hot water sealing: the oxidized aluminum plate is soaked in pure water at 95-100℃ for 20-30 minutes, and the alumina reacts with water to generate "hydrated alumina" (ALO+3HO → 2AL (OH)), which expands in volume to block pores;

Low-temperature sealing: it is soaked in "nickel salt sealing agent" (such as nickel acetate solution) at 60-70℃, and insoluble nickel compounds are generated in pores through chemical reaction, which has better sealing effect and is suitable for products with high weatherability requirements (such as outdoor building aluminum plates).

Third, the third stage: post-processing-giving "appearance and function"

The sealed alumina board has basic performance, and the post-treatment mainly optimizes the appearance or adds additional functions according to the application requirements. The common steps include:

Dyeing (optional): If colorful alumina board is needed to achieve colorful appearance, it needs to be dyed before the oxide film is sealed (porous film can absorb dye molecules);

Organic dyes: such as acid dyes and reactive dyes, which can dye bright colors such as red, yellow and blue, are suitable for interior decoration;

Inorganic dyes: such as chromate (green) and iron salt (brown), which have strong sun resistance and are suitable for outdoor products.

It should be sealed immediately after dyeing to prevent the dye from falling off.

Drying and shaping: to ensure the dimensional stability, put the sealed or dyed aluminum plate into an oven (temperature 80-120℃) to dry and remove the surface moisture; If dimensional accuracy is required, it will be slightly reshaped by leveling machine to ensure the flatness of aluminum plate meets the standard.

Inspection and cutting: screening qualified products and carrying out multiple tests on finished products;

Appearance: check whether there are spots, scratches and uneven dyeing;

Performance: Measure the thickness of oxide film with a film thickness meter, measure the corrosion resistance with a salt spray tester, and measure the hardness of the film with a hardness tester;

Finally, according to the customer's demand, the large-size aluminum plate is cut into the final product specifications (such as plates, coils and special-shaped parts).

Summary: the core logic of alumina board

The whole manufacturing process revolves around "base material purification → electrochemical oxidation film formation → film layer optimization", and the core is to transform "corrosive aluminum plate" into "composite plate covered with wear-resistant alumina film" by anodic oxidation, which not only retains the light weight and easy processing characteristics of aluminum, but also makes up for its poor corrosion resistance, so it is widely used in the fields of architecture, household appliances, electronics, machinery and so on.