After the aluminum and aluminum alloys are treated by the conductive oxidation process, the obtained oxide film still has excellent electrical conductivity, which is its unique performance, and the protective and decorative properties of the film layer are also good, and the film color ratio of the pure aluminum surface is good. The zinc-colored iridescent film of the zinc layer is more elegant, has a lighter and uniform fine grain color, and is a process with great application prospect and popularization value. Next page Stainless Steel Sheet,Stainless Steel Plate,304 Mirror Stainless Steel Sheet Wanlei Steel Pipe Co., Ltd. , http://www.tjsteelpipes.com
The conductive oxidation process of aluminum and aluminum alloy is easy to operate and requires no special equipment. In recent years, the conductive oxide film layer is easy to adsorb organic coating, and the understanding of good bonding force is further improved, so it is used as a substrate for coating (electrophoresis, painting). It has also been gradually expanded.
Specific details to be noted in the pretreatment process
Aluminum materials are extremely unstable in the air, and it is easy to form an oxide film that is difficult to recognize with the naked eye. Due to the different processing methods of aluminum parts, such as casting molding, or directly cutting from the rolled sheet, or mechanical fine processing, or after different processes, heat treatment or welding, the surface of the workpiece will be presented. Different states, different degrees of dirt or traces, for this reason, in the pre-treatment process, the pre-treatment process must be selected according to the actual situation of the workpiece surface.
(1) Problems that need to be paid attention to in the pre-treatment process of fine-worked parts: Although the natural oxide film on the surface is initially formed, it is easier to remove, but greasy, especially in and around the hole (due to machining This kind of workpiece must be cleaned with organic solvent first. If it is directly washed with alkali, it is not only greasy and difficult to remove, but the fine machined surface can not withstand long-term alkali corrosion, and the result will affect the surface of the workpiece. The combination of roughness and tolerance may eventually become a waste product.
(2) Problems that need to be paid attention to in the pre-treatment process of the cast molded part. Not all surfaces of the cast molded parts are machined. The unmachined surface is left with an excessively thick oxide layer formed during the casting process, and some are also covered with a sand layer. In this case, it should be removed first by machining or sandblasting. The original oxide film in this part, or after alkali washing, can only be used to remove the original oxide layer of the unprocessed part and avoid the change of the tolerance of the machined part.
(3) The problems that need to be paid attention to in the pre-treatment process of the workpiece after heat treatment or welding process: according to the process requirements, the workpiece must be cleaned by organic solvent before being transferred to the heat treatment or welding process, except for the surface oil stain, but this is generally not possible. One point, the surface of the workpiece forms a layer of oil-sintered char, which is difficult to remove in organic solvents. If it is immersed in lye, it will cause local corrosion, causing pitting or unevenness, which seriously affects the product. quality. The author used a method of soaking in concentrated nitric acid to soak the char of this layer. After the char is soft, it can be completely removed by a little cleaning in the alkali solution.
Some specific methods of preprocessing are as follows.
1 organic solvent degreasing. If the oil is not too serious, it can be soaked in the solvent for a short time; if the oil is seriously stained, use cotton yarn, solvent, or brush. Pay attention to safety during operation, and keep the remaining solvent after use.
2 dry. Regardless of the organic solvent cleaning method, the drying process must not be omitted, otherwise the meaning of cleaning will be lost.
3 tied. The material used for tying should be aluminum wire, banned copper wire and galvanized iron wire, and the wire of zinc layer can be removed.
Slightly larger single-piece tying should consider the lashing position and be as close as possible to the eyelet closest to the edge of the part to reduce the impact on the surface of the workpiece.
Different kinds of workpieces should not be tied to a string, because the oxidation treatment time of aluminum with different components (grades) is different.
Pay attention to the direction in which the ligated workpiece is suspended, so as to prevent the recessed part from creating a swell due to the downward direction.
Wash the alkali until the oil on the surface of the workpiece is removed.
4 alkaline washing.
5 cycles of water rinse. Rinsing after caustic washing is best done by first flushing with hot water, which is good for washing alkaline substances on the surface of the workpiece. The workpiece with blind holes and slits should be reinforced with the part, and the residual solution should be cleaned and the nitric acid should be turned out to avoid oxidation.
6 nitric acid light. If the treated aluminum and cast aluminum are treated, 50 mL/L hydrofluoric acid should be added to the formulation to accelerate the removal of the insoluble matter adhering to the surface of the aluminum part during the alkaline washing.
Technical requirements for the oxidation film forming process
(1) Oxidation. Solution formulation and working conditions:
Immediately after the pretreatment, it is transferred to the oxidation process to prevent the quality of the oxide layer from being affected by the natural oxide film formed by the workpiece being left in the atmosphere for a long time. Once again immersed in clear water is better than exposure to the atmosphere, but it should not be soaked for too long. If it is soaked in 3% dilute nitric acid, it can still be oxidized within l5~30min, but if it is too long, it will be on the film. The formation also has an effect, especially old nitric acid containing impurities such as copper.
The temperature of the solution during the oxidation process is a crucial process condition. The temperature of the solution is too high, the film formation speed is increased, and the oxide film is prone to chalking. The solution temperature is too low, the film formation speed is slow, and the resulting film is lightly tinted. Poor focus.
In the same type of aluminum, the color of the surface should be the same, and the same time should be treated at the same solution temperature.
Within a certain range, the temperature is inversely proportional to time, that is, the higher the temperature of the solution, the shorter the time required, and the longer the time required.