Study On The Preparation And Properties Of Phosphating And Silane Films On Cold Rolled Steel

The cold rolled steel is widely used in the household electrical appliances, automobiles, industrial equipments and manufacture of construction machinery because of its good performance. However, the cold rolled steel is corroded easily in the application process and often needs to be treatment on its surface to extend service life. In the traditional technology of surface treatment, the phosphating is an important technology of the anti-corrosion. The fast phosphate technology at room temperature, which overcomes the disadvantage of high-energy and high-cost by phosphating in mid-high temperature, is becoming an active technology and be widely concerned. With the development of society, the energy conservation and environmental protection have become the current trend. Therefore, the silane treatment technology that is green environmental protection on cold rolled steel becomes a significant research.This paper studies the process conditions of prepare the phosphate film and silane film at room temperature on the surface of the cold rolled steel, and the modification effect by rare earth modified silane films. The corrosion resistant performances of the films were investigated by linear polarization and CuSO4 dropping, the adhesion between metal substrates and organic coatings were evaluated by immersion in salt-water, and surface structure of the films were characterized by scanning electron microscope(SEM).The optimal formula of the phosphate solution was confirmed through the orthogonal test by taking the discoloration time of CuSO4 as index. The best process conditions were confirmed through the single factor experiment which tested the effect of acid-ratio, immersion time and phosphate temperature on the performance of phosphate film by means of the methods of the linear polarization and the CuSO4 dropping.The cold rolled steel was prepared by silanization on its surface to get bis-(γ-triethoxysilylpropyl)-tetrasulfide(commodity name: Si-69) silane film. The configuration method of the Si-69 solution was confirmed through the single factor experiment which tested by the linear polarization. The best process conditions were confirmed through the single facor experiment which tested the effect of the immersion time, the curing time and temperature on the performance of the silane film by means of the methods of the linear polarization and the CuSO4 dropping.The performances of phosphate film and Si-69 silane film which prepared under the best process conditions were compared with the cold rolled steel. The results of linear polarization and the CuSO4 dropping showed that the phosphate film and the Si-69 silane film obvious enhance the corrosion resistance of the cold rolled steel, and the Si-69 silane film is better than the phosphate film. The immersion in salt-water indicated that the phosphate film and Si-69 silane film can both strengthen the adhesion between the metal substrates and the organic coatings, and the Si-69 silane film is better than the phosphate film. The scanning electron microscope(SEM) showed that there are scratches and potholes in the surface of the cold rolled steel, the surface of the phosphate film is uneven sheet structure with a few voids, the surface of Si-69 silane film is smoother than the phosphate film but there are some linear projections on it.This paper explored to prepare the rare earth modified silane films which doping rare earth chloride in Si-69 silane film to further improve the performance of silane film. Preparing rare earth modified silane films on the surface of cold rolled steel which CeCl3, YCl3, LaCl3 were selected as additives. The optimal amounts of rare earth chloride in Si-69 silane films were confirmed by means of the linear polarization which tested the effect of doping different rare earth chloride in different amounts. Comparing the rare earth modified silane films which prepared under optimal parameter with the Si-69 silane film, the results of the linear polarization and the CuSO4 dropping showed that the corrosion resistance of rare earth modified silane films are better than Si-69 silane film. The immersion in salt-water indicated that the enhancement of adhesion of the rare earth modified silane films between metal substrates and the organic coatings are greater than the Si-69 silane film. The scanning electron microscope(SEM) showed that the surface structure of rare earth modified silane films are uniformly and densely, and the surface are smoothly.