Aluminum and its alloys have been widely used for their superior material properties. At the same time, the decorative and protective technologies on the surface of materials have also been rapidly developed. Among these surface protection technologies, the most commonly used is the anodization, electrolytic coloring, and sealing treatment of the surfaces of aluminum and aluminum alloy materials.
After anodizing the aluminum or aluminum alloy, an oxide film (Al2O3) is formed on the metal surface. The surface of the oxide film is porous, the texture is loose, and the bottom is dense. For aesthetic or other special needs, the oxide film is often subjected to electrolytic coloring, so that the material surface with the color. As the oxide film surface texture is more loose, its wear resistance, corrosion resistance is poor. Therefore, following the oxidation, coloring also need to be closed after the key process.
The principle of the closed treatment is that the porous oxide film is hydrolyzed by hot water or chemical solution to form Al (OH) 3 (a variety of hydrolyzed products are formed in the chemical seal). After the volume expansion, micropores on the surface of the oxide film are filled , Making the workpiece surface wear resistance and corrosion resistance have been greatly improved. At present, people have developed a variety of closed technologies, such as hot and cold boiling water closed, high temperature water vapor closed, the chemical temperature in the closed and cold closed and so on.
Boiling water heat sealing is mainly the workpiece after dyeing in boiling water for about 30 minutes, the current water quality requirements of this process is very high, must be distilled water, and to be deionized, PH value between 5-7, the temperature 98 ℃. High-temperature steam closed by the German proposed a closed process, it is the workpiece after dyeing high pressure, 100 ℃ -110 ℃ closed in the steam. The method closed slightly faster, the effect is slightly better. However, the requirements of high-pressure steam in a closed container, the method of equipment costs are high, not suitable for bulky processing.
Intermediate temperature chemical blocking is the use of strong oxidizing dichromate, at higher temperatures (90 ℃) with the oxide film to generate basic aluminum and aluminum dichromate precipitated alumina and aluminum hydrate pore closed , Is considered a variety of sealing methods in the corrosion resistance of the oxide film is a better sealing technology.
Cold sealing is first proposed by Italy, a closed process, which is immersed in the workpiece at room temperature under the chemical solution mainly NiF2, through the ion exchange and hydration reaction to form Ni (OH) 2, AI (OH) 3 mixed Hydrate deposition, so that the oxide film to achieve closed pore. The method requires low water quality, low energy consumption at normal temperature and short closing time. The disadvantage of technology is that nickel has serious environmental pollution and personal damage, so far the method has not gained international recognition.
The existing closed process basically meets the needs of conventional applications, but in some areas demanding surface cleanliness (such as inertial confinement fusion, aerospace, etc.), most of the above closed process can not meet the requirements. After closed parts wipe with alcohol will appear a lot of fading phenomenon, the surface of the oxide film wear resistance and corrosion resistance is poor, easy to clean the environment caused by pollution. The individual process to meet the requirements of its high cost, is several times the ordinary process.
In order to solve this problem, Yan Yadong, Wang Feng, He Junhua and other researchers in Advanced Optical Technology Research Institute of Xi'an Institute of Optics and Fine Mechanics, Chinese Academy of Sciences put forward a kind of aluminum alloy anodization electrochromic sealing process. Due to the gradual decrease of hydrolysis temperature and long period of the whole process, the hydrolysis process gradually slows down quickly, which provides enough time for the hydrolysates to fully and densely adhere to the oxide film surface. By slow cooling to room temperature, the phenomenon of rapid dewatering and cracking of the hydrolyzed membrane caused by rapid cooling of the workpiece in the conventional boiling water sealing process can be avoided, and the surface cracks greatly reduce the wear resistance and corrosion resistance of the surface.
After the invention of the ordinary anodized black workpiece after the closure, repeatedly rubbed with scouring cloth dip alcohol, scouring cloth as ever. "Aluminum alloy anodic oxidation electrolytic coloring of the closed process" technology is simple, low cost, pollution-free, good sealing effect, inertial confinement fusion and space load has been verified, has been authorized by the national invention patent.