独步全球原因
Coil anodized aluminum panels
Competitive edges
Popularization of knowledge: labeling of aluminum plates
- A. The 1000 series of aluminum panels, represented by the 1050, 1060, 1070 and 1000 series, are also called pure aluminum panels, and contain the largest aluminum contents among all series of products. The purity can reach above 99.00%.As no other technical elements are included, the production processes are relatively simple and the prices are relatively cheap, making this series of products the most commonly used one in the conventional industry. At present, the demand for the 1050 and 1060 series of products rank the top in the market. For the 1000 series of aluminum panels, the last two Arabic numerals of their serial numbers indicate their minimum aluminum contents. For example, the last two Arabic numerals of the 1050 series are 50, conforming products shall contain an aluminum content of 99.5% and above according to the international nomenclature of product codes. China's aluminum alloy technical standard (GB/T3880-2006) also clearly stipulates that the aluminum content of 1050 series of products shall reach 99.5% and above. Likewise, the aluminum content of the 1060 series of aluminum panels must reach 99.6% and above.
- B. The 2000 series of aluminum panels, represented by the 2A16 (LY16) and 2A06 (LY6) series, are featured with high hardness, and contain the largest content of copper, reaching up to about 3-5%.The 2000 series of aluminum panels are designed for aerospace purposes and are not commonly used in conventional industries at present. There are not many domestic manufacturers that produce 2000 series of aluminum panels, while the quality is still as not competitive as that of imported ones. So far, most of imported aluminum panels are provided by South Korean and German manufacturers. With the development of China's aerospace industry, the production technology of the 2000 series of aluminum panels will be continuously improved.
- C. The 3000 series of aluminum panels are mainly represented by the 3003, 3003 and 3A21 series. It is also called rust-proof aluminum panels. China's manufacturing technique of the 3000 series of aluminum panels is relatively advanced. Manganese is a main composition of the 3000 series of aluminum panels, and its content is between 1.0-1.5%.This series of products have outstanding rust resistant performance, and are commonly used in the production of air conditioners, refrigerators and chassis of vehicles that are used in the moist environment; the 3000 series of products have higher prices than those of the 1000 series, and are widely used in lots of fields.
- D. The 4000 series of aluminum panels, represented by the 4A01 and 4000 series, contain higher silicon contents, which are normally within 4.5-6.0%.This series of products are commonly used in construction, machinery, forging and welding industries, and they are featured with low melting points, outstanding corrosion resistance, high thermal resistance and wear resistance performances.
- E. The 5000 series of aluminum panels are represented by the 5052, 5005, 5083 and 5A05 series. This series of products also have wide applications and contain higher magnesium, with the contents of 3-5%.Therefore, it is also known as the aluminum-magnesium alloy. It is mainly featured with low density, high tensile strength and high elongation. The weights of aluminum-magnesium alloys are smaller than those of other series of aluminum alloys of the same volumes; that is why they are commonly used in the aviation industry, e.g. the production of aircraft fuel tanks. This series of products also find wide applications in conventional industries. As these products are hot-rolled aluminum panels that adopt the processing technology of continuous casting and rolling, they are available for oxidation processing. In China, the manufacturing technique for the 5000 series of aluminum panels are comparatively mature in the international market.(Most of the products provided by the COIL company are the 5005 series)
- F. The 6000 series of aluminum panels, mainly represented by the 6061 series, contain higher magnesium and silicon elements; it adopts the manufacturing technique of cold forging, and combines the advantages of 4000 series and 5000 series, making it suitable for applications that have high requirements of corrosion and oxidation resistance. It is featured with outstanding usability, interface characteristics, easy to coat and good processability, and is commonly used in low pressure weapons and aircraft joints.
General characteristics of the 6061 series: excellent interface characteristics, easy to coat, high strength, high usability and corrosion resistance.
Typical applications of the 6061 series of aluminum panels: aircraft components, camera parts, couplers, marine parts and hardware, electronic parts and fittings, decorative or various hardware, hinged joints, magnetic heads, brake pistons, hydraulic pistons, electronic parts, valves and valve parts. - G. The 7000 series of aluminum panels, represented by the 7075 series, contain higher Zinc elements. This series of products are also commonly applied in the aviation industry; as it contains aluminum, magnesium, zinc and copper elements, it has ultra-high rigidness and outstanding wear resistance, and it is available for heat treatment. As the 7075 series of aluminum panels are stress-relieved, no deformation or warping would happen after being processed. All the ultra-thick and ultra-thick 7075 series of aluminum panels are subject to ultrasonic flaw detection to ensure no blisters or impurities. The 7075 series of aluminum panels have high thermal conductivity, which can shorten the forming time and improve the working efficiency. As the 7075 series of products are featured with high hardness and strength, they are commonly applied in the production of aircraft components, high stress structural components and molds which have strict requirements for strength and corrosion resistance. At present, the domestic market mainly depend on the import of this series of products, and domestic manufacturers still need to improve the manufacturing technique.(A foreign company once pointed out the uneven annealing problem of the 7075 series of aluminum panels manufactured by our company, and uneven annealing would cause nonuniform of the surface and internal hardness of the panels)
- H. The 8000 series of aluminum panels, commonly represented by the 8011 series, belong to other series of aluminum panels. Most of this series of aluminum panels are formed into aluminum foils and are used for the production of bottle caps and radiators. This series of products have little demand in the market.
- I. The 9000 series of aluminum panels belong to the spare series, which allow the contents of other alloy elements. the International Aluminum Panel and Strip Association specially states that the 9000 series is a spare series, preparing for the emergence of another new variety of aluminum panels to fill the blank.
The oxide film is not thick enough, will it lose color?
Let's take a look at the impacts of insufficient thickness of oxide film.
Generally, the thickness of the oxide film should be 10 μm or more for dyeing. Once the thickness is not enough, the dyeing is vulnerable to unevenness!
Therefore, insufficient thickness of the oxide film will lead to uneven color rather than losing colors.
Generally, the thickness of the oxide film should be 10 μm or more for dyeing. Once the thickness is not enough, the dyeing is vulnerable to unevenness!
Therefore, insufficient thickness of the oxide film will lead to uneven color rather than losing colors.
- I. The principle of oxidation dyeing
It is well known that the anodized film is composed of a large number of hexagonal unit cells perpendicular to the surface of the metal, and each unit cell has a pore in the center that has a strong adsorption force. When the oxidized aluminum product is immersed in the dye solution, the dye molecules will enter the oxide file through the pore under the effect of diffusion, and at the same time form covalent bonds and ionic bonds which are difficult to separate from the oxide film. However, such bonds are reversible, and desorption occurs under certain conditions. Therefore, after dyeing, it is necessary to seal the pores to fix the dye in the pores and increase the corrosion resistance and wear resistance of the oxide films. - II. The effect of anodizing process on dyeing
In the entire process of oxidation dyeing, poor dyeing due to oxidation process is relatively common. The thickness of the oxide film and the uniformity of the pores are the premise and basis for obtaining a uniform color during dyeing. In order to obtain an uniform oxide film, sufficient circulation and cooling, as well as excellent conductivity, shall be guaranteed, and the stability of oxidation process is also indispensable.
The concentration of sulfuric acid needs to be controlled within180-200g/l. A slightly higher concentration of sulfuric acid can promote the dissolution reaction of the oxide film, which facilitates the expansion of the pores and make it easier for dyeing process; The concentration of aluminum ions shall be controlled within 5-15g/l. When the concentration of aluminum ions is lower than 5g/l, the adsorption capacity of the oxide film formed will decrease, which negatively affects the dyeing speed. When the concentration is larger than 15g/l, the uniformity of the oxide film will be negatively affected, leading to an uneven film.
The oxidation temperature shall be controlled at about 20°C. The temperature of the liquid inside the oxidation tank has a significant effect on the dyeing. If the temperature is too low, the pores of the oxide film will be densified, which largely decreases the dyeing speed; if the temperature is too high, the oxide film will become loose and vulnerable to be powdered, which is not conducive to the control of dyeing; the temperature variation of the liquid inside the oxidation tank shall be controlled within 2°C.
Current density shall be controlled within 120-180a/m2.If the current density is too large, the electrolysis time of aluminum products inside the tank is shortened correspondingly when the film thickness is constant; thus, the dissolution of the oxide film in the solution is reduced and the pores of the oxide film become densified, leading to the increase of the dyeing time. At the same time, the film is vulnerable to be pulverized.
Generally, the thickness of the oxide film should be 10μm or more for dyeing. Too small thickness easily leads to uneven dyeing. When dark colors (e.g. black) are to be dyed, if the thickness of the oxide film is insufficient, the deposition of dyes will be limited, making it difficult to reach required intensity of colors. In summary, anodizing is the former working procedure of and the basis for dyeing. However, it is difficult or even impossible to observe the problems of anodizing before dyeing, while negative effects will be obvious after dyeing. At this moment, operators often attribute the causes of the problems to abnormal dyeing, but ignore the improper process of oxidizing. Such mistake happens a lot when we have not learnt sufficient experience in oxidation dyeing. - III. Dyeing
- 3.1 Rinsing before dyeing
After anodizing, residual sulfuric acid solution will remain in the pores of the oxide film; therefore, aluminum products must be thoroughly rinsed before dyeing. In order to avoid bringing impurity ions into the dyeing tank, especially phosphate ions and fluoride ions, etc., rinse the products before immersing them in the dyeing tank; it is necessary to monitor the quality of the rinsing water. - 3.2 Preparation of the dyeing tank
Most of the dyes used for dyeing are organic, which are easy to get mildewed. In order to prevent the tank from getting mildewed, the tank should be sterilized with bleaching powders or phenol-like substances before preparing the solution. When preparing the dyeing solution, adding certain mildew-retarding agents can effectively extend the service time of the solution. Prepared dyeing solution should be stored for several hours before being put into use; acetic acid-sodium acetate buffer solution can be added to ensure the stability of the pH values. - 3.3 Control of the dyeing process
(1) Temperature
During the dyeing process, the dyeing rate increases with the rising of the temperature; thus, the dyeing time required for a certain depth of color decreases with the rising of the temperature. At the same time, with the temperature rising of the solution inside the tank, the synchronous sealing of the pores will also speed up. If the temperature is too high, the synchronous sealing of the pores will accelerate dramatically, and as a result, insufficient amounts of dye molecules are not adsorbed in the pores and required intensity of colors cannot be obtained; when the dyeing is carried out in relatively low temperatures, stronger intensity of colors can be obtained while longer dyeing time is needed; therefore, the dyeing temperatures should be adjusted appropriately according to different requirements of colors, so as to control the dyeing time.
(2) Concentration of dyes
According to the adsorption law, under certain working conditions, the adsorption amount of dyes on the anodized film increases with the rising of the concentration of dyes. However, this law is only applicable when the oxide film still has the adsorption capacity. For different intensities of colors, the concentration of dyes should be adjusted accordingly. When the solution inside the tank is initially prepared, a lower concentration should be prepared as much as possible. As the production progresses, the dyes will be continuously consumed, and the consumed proportion shall be continuously replenished. The replenishment should be conducted in multiple times, with small amounts for each time. When the concentration of dyes is measured, impurity ions should be taken into consideration. As the actual effective concentration may be largely different from measured values, the actual dyeing power of the dyeing solution should be tested on a regular basis. In order to ensure a stable dyeing power, the dyeing solution should be partially replaced after a period of production.
(3) Time
Like electrolytic dyeing, when other conditions remain the same, the colors dyed gradually deepens with the increase of dyeing time. Generally, under given oxidation conditions, the concentration and temperature of the dyeing solution are determined. Therefore, we obtain the colors required by customers only by adjusting the dyeing time. If required colors are obtained within a short period of time, there will be two disadvantages: the colors dyed are easy to be uneven and required weather resistance may not be achieved. If the dyeing time is too long or the desired color intensity cannot be obtained no matter how long it takes, we should consider whether the oxide film is too thin or the concentration of the dyeing solution is too low.
(4) pH value
Generally, the pH value shall be within 5~6. A stable pH value is very significant for dyeing. Especially for mixed dyes, different pH values may generate different color tones. To enhance the stability of pH values, adding a buffer solution during the preparation of the dyeing solution is a feasible method; at the same time, it is necessary to strengthen the rinsing operation before dyeing to avoid bringing into acidic substances. - 3.4 Rinsing after dyeing
After dyeing, it is necessary to rinse the aluminum products with water to remove the floating colors attached to the surface of the aluminum products. At this time, pay attention to the water quality in the rinsing tank because the bonding of the dye molecules and the oxide film is reversible; when there are many impurity ions in the water, the dye molecules will be separated from the oxide film and go into the water, resulting in color fading. Such color fading is always uneven, which eventually leads to color difference on the same piece of materials.
- 3.1 Rinsing before dyeing
- IV. Sealing of pores
The sealing of pores is an indispensable procedure for anodization. After oxidation dyeing, original colors of dyed films can only be remained after the sealing treatment. There are a variety methods of sealing, such as steam sealing, hot water sealing and medium temperature sealing; cold sealing is available for some dyes. After the sealing of pores, the color may fade slightly, but much attention are not necessary.
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