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Author: Marisa
1. Overcoming the coarsening effect
Surface adjustment can overcome the coarsening effect after strong acid and strong alkali treatment. Generally speaking, strong alkaline solutions usually have the effect of coarsening the phosphate film crystals. After the metal workpiece is degreased with strong alkali, due to the poor water washability of some alkalis, such as sodium hydroxide and sodium silicate, some active crystal nuclei on the metal surface are often covered with a layer of hydroxide or oxide film, resulting in a decrease in the number of crystal nuclei on the metal surface and the free energy of the reaction, thus making the phosphate film rough and porous, and the film formation is incomplete. Therefore, the metal workpiece should be surface adjusted after degreasing with a strong alkaline degreasing agent. After the metal workpiece is pickled and rusted, the metal will produce a rough surface due to acid corrosion. Although this increases the effective surface area of the metal, which may also be part of the reason for the increase in the weight of the phosphate film after pickling, it also reduces the active points on the metal surface, thus also producing a rough phosphate film. After the metal workpiece is surface adjusted, the active and inactive points on the surface of the metal workpiece can be homogenized, eliminating the defects of uneven corrosion caused by strong alkali degreasing or strong acid derusting of the metal workpiece, thereby overcoming the coarsening effect brought about by strong acid and strong alkali treatment.
2. Accelerate the phosphating speed
Surface adjustment speeds up the phosphating reaction and reduces the temperature of phosphating treatment. Surface adjustment increases the active points on the metal surface, providing the nuclei for the growth of phosphating film, so that the metal surface starts to form film immediately when it contacts the phosphating solution, greatly speeding up the initial film formation speed of the phosphating film, thereby shortening the phosphating time. According to relevant information, the phosphating time of the workpiece can be shortened by about 1/2 after surface adjustment. In addition, surface adjustment can also reduce the phosphating temperature, reduce energy consumption, and improve the phosphating environment in winter, which is an indispensable condition for low-temperature and room-temperature phosphating.
3. Refine the phosphate film grains
Surface adjustment refines the grains of the phosphate film and improves the appearance of the phosphate film. After the surface of the metal workpiece is adjusted, the crystal nuclei formed by the contact between the active points on the metal surface and the phosphating agent are extremely fine. According to relevant information, the crystal size of the phosphate film can be reduced from 40um to below 20um, which not only prevents the formation of large crystal nuclei, but also prevents the formation of iron phosphate blue film. The generated phosphate film has fine crystals, which improves the appearance of the phosphate film, enhances the bonding strength between the phosphate film and the metal surface, and improves the corrosion resistance of the phosphate film.