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July 14, 2022
Influence of Sandblasting and Chemical Sand-surfaced Method on Anodic Oxidation of Aluminum Profile Surface
Two methods of surface pretreatment of aluminum profiles:
Chemical alkaline etching sand washing method and
The traditional surface pretreatment process of sand-surfaced aluminum profiles is to use chemical sand-surface method, and use alkaline etching to wash the surface to form a sand surface. However, this is an unreasonable process with large aluminum consumption, alkali consumption and acid consumption. In recent years, the mechanical sand surface method has been successfully used in the surface pretreatment of aluminum profiles. Many manufacturers in my country have used sand blasting to replace chemical alkali etching, which has achieved remarkable results in improving product quality, reducing costs and reducing environmental pollution. .
However, the sand surface formation mechanism of these two processes is different, and the surface and surface state after surface pretreatment also have important differences, which directly or indirectly affect the performance of the anodized film.
1. Sand surface formation mechanism
The chemical sand surface method is to achieve the purpose of sand surface by the turbidity of metal materials in alkaline solution.
The mechanical sand surface method, that is, the sand blasting method, has a completely different sand surface formation mechanism. Sand blasting uses compressed air to shoot different abrasive grains on the surface of the aluminum profile. The mechanical sand blasting process has both the cleaning effect of sand blasting and shot blasting. surface strengthening.
The formation mechanism of the sand surface is that the sharp surface of the aluminum material becomes flat under the impact of shot peening, while the originally smooth surface becomes rougher than the original under the action of the abrasive, and finally a certain roughness is formed on the surface of the aluminum profile. Uniform and fine hemp surface, sandblasted surface treatment can eliminate extrusion stripes and scratches on the surface of aluminum profiles.
2. The effect of surface morphology on the performance of anodized film
It can be seen from the formation mechanism of the sandblasted surface that the sandblasting process will have a greater impact on the surface morphology of the aluminum profile. The two samples were tested with a hardness detector and a scanning electron microscope (SEM), and it was found that the surface morphology parameters of the aluminum profiles under the two process conditions were quite different. After washing and polishing, the exposed base metal is much smoother than sandblasted materials.
In eliminating extrusion streaks and scratches, the sandblasting process has more advantages than the alkaline washing process, and its horizontal and vertical roughness values are basically the same, obviously it can obtain a more uniform sand surface than the chemical sand surface process.
3 Influence of surface structure on anodizing
The impact of sandblasting abrasive during sandblasting will cause changes in the surface structure of the aluminum profile. During sandblasting, the surface metal will undergo severe plastic deformation under the impact of high-speed projectiles, and the crystal will slip along with the plastic deformation process, resulting in sub-grain With the increase of the dislocation density in the grains, the lattice spacing changes, and a finer microstructure will be obtained on the surface layer after sandblasting.
Under different pretreatment conditions, due to the different sand formation mechanisms, there are also essential differences in the surface microscopic morphology, surface crystal structure and surface activation energy of aluminum profiles, which will directly or indirectly have an important impact on the performance of the anodized film. influences.
In order to obtain qualified products, a reasonable surface pretreatment route and optimal process parameters must be established, such as the properties of abrasive particles in the sandblasting process
At present, the surface treatment of aluminum profiles often chooses sandblasting and anodizing, that is, the aluminum profile workpieces are first subjected to sandblasting surface treatment, and then anodized.
Anodic oxidation, the electrochemical oxidation of metals or alloys. Under the corresponding electrolyte and specific process conditions, aluminum and its alloys form an oxide film on the aluminum product (anode) due to the action of the applied current. Anodizing usually refers to sulfuric acid anodizing unless otherwise specified.
Because of its high sphericity, moderate density, good elasticity, uniform sandblasting effect, low dust and no metal pollution, ceramic beads has become the most commonly used sandblasting abrasive in sandblasting and anodizing of aluminum profiles.