Causes of poor oxidation of aluminum alloy processing

- Mar 15, 2019-

It mainly introduces the knowledge of aluminum alloy processing such as the precautions in the aluminum alloy processing pretreatment process, the technical requirements of the oxidation film forming process, and the possible causes of the uneven color of the oxide film.


Aluminum alloy processing


Aluminum and aluminum alloy color conductive oxidation


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.


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 coating (electrophoresis, painting) substrate. It has also been gradually expanded.


1. 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 it is 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 of this part is either processed by alkali washing and the only way to remove the original oxide layer of the unprocessed part and avoid the change of the tolerance dimension of the machined part.


(3) 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, local corrosion will occur, causing pitting or unevenness, which will seriously affect 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.


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