(1) alkali flow mark. This defect is produced during the alkaline etching process, and its morphology has obvious traces of flow, as well as the direction of flow. If the alkali etching temperature is high, the walls of industrial aluminum profiles are thick and the structure is complex. The continuous alkaline etching reaction releases a large amount of heat, which results in high temperature of the alkaline etching bath fluid and local continuous overheating of the aluminum profile surface. Accelerated etching, the formation of alkali flow marks. The solution to the alkali flow mark is to reduce the temperature of the alkaline etching bath. When this defect occurs, it is advisable to reduce the temperature of the alkaline etching bath by at least 10°C. The loading of the profiles should be uniform and the spacing should be moderate. To prevent overfilling, causing local overheating and alkali flow marks.

      (2) Fingerprint erosion. The feature of this defect is pitting corrosion with the shape of a handprint. This is caused by the fact that the operator did not bring clean gloves and did not carry out the necessary protections and moved the industrial aluminum profiles directly. This is caused by sodium oxide, lactic acid and other substances in human sweat. The pitting of hand fingerprints can sometimes be very deep. Fingerprint corrosion is likely to occur on aluminum substrates, and the activation of the surface of the aluminum substrate after alkaline etching is more likely to appear fingerprint corrosion. With this defect in aluminum products, there is no ready-made method to restore its original appearance. Therefore, it is important to prevent the product from being carried with clean gloves. Unclean gloves will also have similar defects. Aluminum fingerprints with slight fingerprint corrosion can be removed by mechanical and manual grinding, followed by cleaning, alkaline etching, etc., but the consistency of the surface and adjacent surfaces must be observed during production.

     (3) The anodic oxide film is not completely removed. This defect is caused by uneven uneven marks on the surface of the re-anodized industrial aluminum profile, which was caused by the fact that the previous anodized film was not de-exhausted. When anodizing is performed again, a new anodized film is formed on the partial surface of the anodized film, and a part of the surface of the anodized film that has not been degenerated is unable to form a new oxide film due to its presence, and thus the anodized film is not formed. Uniform and rough marks. If it is necessary to perform the coloring treatment, the surface of the anodized film that has not been completely removed cannot be colored. The solution to this defect is to strengthen management, improve the level of operation, and increase primary yield. For industrial aluminum products that have been sealed, they should be immersed in a nitric acid ash removing tank to remove the sealing effect and ensure that the oxide film can be evenly degassed.

(4) bright patterns. This defect is the obvious form of preferential etching of aluminum extrusions, producing a bright grain-dispersed pear-like pattern in alkaline etching. With the increase in the amount of dissolved zinc in the alkaline etching bath solution, there will be differences in the dissolution of crystal grains and grain orientations, turning into a glittering bright pattern, and this phenomenon becomes clear along with the progress of alkaline etching. In alkaline etching baths, this defect is more pronounced with the increase of the zinc content. It has been determined that this defect will occur when the dissolved zinc content is 4 μm/g. This defect is not likely to occur when the zinc content in the aluminum profile is above 0.05%. It is also affected by grain size, grain orientation, and the like. Solution to the problem: The removal of the zinc content from the alkaline etching bath and the addition of a small amount of sodium sulphide (theory, a slight excess in theory) to precipitate, this method is more successful than its use in long-lived alkali etching additives. It is not as good as the alkali etching solution used in the sodium gluconate system to reduce the zinc content in the aluminum alloy. An efficient grain refiner is used to increase the deformation of the aluminum alloy and prevent grain coarsening.

     (5) Superficial corrosion. The aluminum substrate is not susceptible to corrosion under normal conditions, but slight superficial corrosion may sometimes occur. However, the aluminum substrate is stored in a humid, contaminated atmosphere, usually an acid mist. If moisture condenses on the aluminum, moisture condensation from the overlapping edges of the aluminum material penetrates into the center, and a large area occurs. The obvious shallow corrosion is that the upper and lower surfaces have the same symmetric corrosion morphology. After exposure to rain, especially acid rain, aluminum materials are prone to shallow corrosion. At present, there is no satisfactory method to remove superficial corrosion. Only the storage and transportation conditions of aluminum substrates are strengthened, and dry storage is carefully managed to avoid superficial corrosion. A precautionary approach should be adopted. After the aluminum substrate is produced, the surface treatment should be performed within 3 days. If it is necessary to keep the partner substrate for a long time, the traditional method is to use rust-proof oil coating to protect it. Agent in sealed plastic packaging. Usually stored in a warehouse with desiccant, transport should be rain and moisture, aluminum substrate that has been shallow corrosion can be manually or mechanically polished method, mechanical brushing or sandblasting method can also be used to remove light Table corrosion.

     (6) Alkali burns. This defect is uneven gloss caused by excessive reaction of alkali etching bath liquid remaining on the surface of the aluminum material. After the aluminum material is alkali-etched and then transferred into the water-washing process, the residual bath solution on the surface of the aluminum material is excessively reactive, and part of it becomes dry, making the etched surface uneven, resulting in non-uniform gloss. The reason for this is that the alkaline bath solution is aging, and the sodium hydroxide content is out of control, which is often high. If the bath temperature is too high, the temperature is high, and the transfer time is too long, alkali burns are more likely to be caused. The measures to prevent alkali burn are to strengthen the analysis and maintenance of alkali etching bath, control the amount of sodium hydroxide and aluminum in the specified range, correctly control the temperature of alkaline etching bath, strengthen the management of production operation, and correctly grasp the transfer. Operating time, wash immediately after alkali etching.

     (7) Over-etching. Excessive alkaline etching of the profile will turn into a rough pear-like surface, which not only reduces the gloss, but also excessively etched dissolves the aluminum profile, even affecting its dimensional accuracy and mechanical properties. Due to changes in alkali etching process factors such as sodium hydroxide content, temperature, etch time, frequent rework processing, and other inappropriate operating process factors, excessive alkali etching may occur. In addition, variations in alloy composition, processing conditions, and additives may also cause excessive alkali etching. When the defect is severe, rough or pitting corrosion occurs on the surface of all or part of the aluminum material. Aluminum has been over-etched, which may be related to incorrect analysis of the bath solution, lack of proper production or long-term loss of bath maintenance. The occurrence of severe rough overetching defects may have a great relationship with the increase in the alkaline etching rate. At this time, the etch rate of industrial aluminum profiles is more than three times greater than the normal etch rate. Under such etching conditions, if the hydroxide adheres to the surface of the aluminum material, serious localized etching occurs, and the local temperature rises, sometimes accompanying grain boundary erosion. There has been erosion, and the direct rescue measure is to reduce the temperature of the bath by 10-20°C, but to adjust the content of the alkaline bath to the correct range, it should be restored to the normal production operation as soon as possible. The alkali bath composition and working conditions (such as sodium hydroxide content, aluminum content, temperature, etc.) should be selected to control the alkali etching operation time, and the maintenance and management of the bath fluid should be enhanced to reduce the number of rework of aluminum profiles.

     (8) Galvanic corrosion. Galvanic corrosion may occur in the water washing process. It appears in the form of pitting corrosion and has the possibility of increased corrosion. There is a white corrosion product around the pitting corrosion. The cause of galvanic corrosion is that two different potential metals (such as aluminum and steel tanks) are immersed in the water containing the electrolyte and connected to each other. Because the potential of the industrial aluminum profile is relatively negative, the profile is subject to accelerated corrosion. . The solution to galvanic corrosion is to prevent the conductive beam from being placed directly on the edge of the steel groove. Effective electrical insulation measures should be taken to prevent the electrical insulation from getting wet by the bath and water. It is also necessary to carefully protect the production. The process tanks in the process are protected against stray currents. The steel tanks should be grounded exclusively, especially the steel wash tanks.