Preparation And Performance Of Surface Tolerant Residual Rust Zinc-rich Coating And Its Intermediate Coating

The surface tolerant residual rust coatings can be painted onto the surface rusted directly,which can avoid the treatment before painting, save large amounts of expenditure and reduce the harm for the environment, constructers and have better properties than traditional coatings. In recent years the residual rust coatings have became hotspots and focuses in the studies of heavy-duty coatings. The atmospheric corrosion of hot-dip galvanized steel and development of residual rust coatings are reviewed in details. In this thesis, an organic rust conversion solution was prepared, and with the rust converter we have got the surface tolerant residual rust zinc-rich coating incorporating stabilization, transform, permeate into an organic whole. On the basis of conventional intermediate coating can't cooperate well with residual rust primer, the Al-rich epoxy coatings modified with aluminium zirconium coupling agent was prepared. The main points of this dissertation are summarized as follows:1,Preparation and investigation of organic rust converter for hot-dip galvanized steel. Morphology and composition of the hot-dip galvanized steel was studied using the scanning electron microscopy (SEM) and energy dispersive x-ray (EDS) . To investigate zinc atmospheric corrosion in the presence of chloride alternate wet and heat test has been employed, the texture of the corrosion products were evaluated employing X-ray diffraction. According to the experimental results, an organic rust conversion solution which had several functions such as phosphorization, passivation, oil removal was prepared. The physical properties, and corrosion protection of hot-dip galvanized steel were studied. The results exhibited the organic rust converter could formed a compact and uniform film, the film adhesive force did not exceed 2 grade, the film could resist cupric sulfate spot test for 162 S and dipping test in the 3%NaCl solution for 17 h. Besides, the antirust time could be up to 50 days,conversion efficiency reached 0.124 Kg·m^-2.2,Preparation and evaluation of surface tolerant residual rust zinc-rich coating. During the preparation, the epoxy resin E-44 was selected as the main film former and polyvinyl butyral resin, amino resin, epoxy-silicone resin as the auxiliary materials. The flake zinc powder and multiple antirust pigments were used to improve corrosion resistance of the coatings. The organic rust conversion solution prepared in chapter 2 was used as one component of coating. The physical mechanical properties, anticorrosive properties, application over rust and construction performance of the coating were optimized by orthogonal experiments. The coating showed good physical mechanical properties, the pencil hardness reached 4 H. After immersing in 3%NaCl solution for 60 days or salt spray test for 800 h the coating had no blister and rust spot. The effect of rust converter on the corrosion resistance of residual rust coatings application over metal without rust was investigated by salt spray test. The results indicated coatings exhibited the highest protective performance while 6 qualities ratio rust converter was used.3,Preparation and performance study of Al-rich epoxy coatings modified with aluminium zirconium organic metal coupling agent. The surface of Al flake powder was modified by aluminium zirconium coupling agent. The resulting flakes were incorporated into epoxy coatings as anticorrosive pigments. The EDS and SEM tests indicated that the coupling agent improved the dispersion of Al flake powder, and the spot-like surface defects were repaired, so the flatness, adherent and shielding effect of coatings was greatly enhanced. Meanwhile, the coatings modified with 2.5wt% aluminium zirconium coupling agent displayed good physical mechanical properties, the pencil hardness reached 4 H. After exposure of simples in 3% NaCl solution for 65 days, no blister and rust spot was found on the surface. The electrochemical impedance spectroscopy (EIS) results of coatings in 3.5% NaCl solution showed that after 52 days immersion the coatings before modification had no corrosion resistance, the coatings after modification still displayed good corrosion protection with impedance value of 10⁶Ω·cm² and the epoxy coatings exhibited the highest protective performance while 2.5wt% coupling agent was used. Tafel test indicated the coatings displayed smaller corrosion rate after modification. The test of supporting system showed the intermediate coating cooperated well with primer, composite coating system exhibited good corrosion performance, cold and hot fatigue property, retractility.