improve, the traditional coating ternary phosphating pretreatment materials containing P, Mn, Ni and other heavy metal pollutants are gradually prohibited by local regulations, Zirconium the new green phosphorus-free conversion Membrane technology gradually mature and rapid development, the process can not completely use P, Mn, Ni, nitrite and other harmful substances, there are mainly zirconium salt pretreatment process, silane pretreatment process. Zirconium On the same substrate, non-phosphorus pretreatment of nanocrystalline film and ternary phosphating film has considerable corrosion resistance, the current domestic new planning coating plant will generally consider the non-phosphorus pretreatment process, the traditional phosphating production line Also gradually began to switch to non-phosphorus production line.
Zirconium salt conversion film is zirconium (H2ZrF6) as the main body, Zirconium the metal substrate in the zirconium hydrochloric acid solution in the electrochemical reaction to form a layer of nano-inorganic film
Ternary phosphating film thickness of 2 ~ 3μm, zirconium salt conversion film thickness of 20 ~ 50nm, observed in a scanning electron microscope (SEM), zirconia film is more dense than ordinary phosphating film (Figure 1, Figure 2) The Phosphine film membrane between the gap, the film began to dissolve after dissolution, and gradually spread to the surrounding; zirconia film dense, no gap between the membrane, Zirconium not easy to produce the membrane dissolved, which has excellent corrosion resistance.
The results of the comparative test show that the galvanized sheet is comparable to the anticorrosive ability after the zirconium and the pretreatment of phosphating, but there are differences in the treated aluminum plate and the cold rolled sheet. Aluminum plate after the anti-corrosion treatment after the corrosion resistance than the zirconium treatment is poor, the maximum corrosion width of more than 2mm, and zirconium treatment of aluminum almost no corrosion, mainly aluminum through ordinary phosphating treatment, there can not be on the membrane or membrane precipitation Of the phenomenon, can not achieve the effect of corrosion, so phosphating in the treatment of aluminum when the need to adjust the content of F in the treatment solution to increase the amount of corrosion of F ions on the plate in order to achieve corrosion requirements. The corrosion resistance of the cold-rolled plate after zirconization treatment is weaker than that of phosphating treatment. The maximum corrosion width is 4mm, mainly the zirconium film is too thin, and the anticorrosive ability is poor after electrophoresis.
The traditional lead-free electrophoretic paint supporting zirconium salt pretreatment inner plate electrophoresis almost no film, the use of four box method for swimming penetration test, test data as shown in Table 2, the results show that: traditional electrophoretic paint 1 # matching zirconium salt pretreatment is not Can be film, mainly zirconium pretreatment film is thin, relative to the phosphating pretreatment of the membrane impedance is low (about 1/20 of the phosphine film), and electrophoresis of the swimming force and pre-treatment of membrane impedance R0 is proportional to the resistance of the electrophoretic paint R is inversely proportional to , so supporting the pre-treatment of zirconia need to improve the swimming penetration of electrophoretic coating, improved after the high swimming electrophoretic paint 2 #, swimming force can reach 60% about.
Zirconium process and traditional phosphating process, in addition to the film structure, corrosion resistance, and electrophoretic paint supporting the existence of differences, Zirconium the equipment, process parameters, white body quality control and other aspects of the construction process there are some differences.
1) zirconium process to replace the traditional phosphating, in order to prevent the process before the impurity into the zirconium tank pollution tank, the original table trough switch to a pure water tank, Zirconium the table groove to the tank to wash all, cleaning sediment , Phosphating pollutants as close as possible to 0; pre-degreasing, degreasing tank oil and water separation device if there is foreign body, Zirconium iron powder must also use high pressure water gun cleaning, to prevent iron slag contaminants into the zirconium tank.
(2) zirconium film is thinner than phosphating film, if there are impurity ions will affect the film, so the traditional phosphating tank switch to zirconium tank before the need for the original phosphating process generated phosphating slag and other residues (Including the zirconium tank, replacement tank, Zirconium sedimentation tank, fill tank, etc.), usually using high pressure water gun cleaning and nitric acid cleaning the original tank and pipe, Zirconium clean the dirty line, the nozzle needs to be disassembled cleaning or Replacement (Figure 14 red standard piping need to focus on cleaning), after cleaning to ensure that the original phosphating slag content of less than 50ppm, to ensure the quality of zirconium film.
(3) zirconia film thinner about 20-50nm, the substrate of the cover force, anti-oil pollution ability is poor, so the white body needs to strictly control the white body in the welding, stamping use of grinding materials, anti-rust oil.