Preparation And Corrosion Resistance Of Silane Films On Surface Of Cold Rolled Steel

Due to the advantages of the low power consumption and environmental benignity,silane treatment technology on metal surface has been attracted a great deal of attention in this area.In this thesis,single silane film and composite silane film on the surface of cold rolled steel were prepared,using cerium salt compound,serpentine and magnesium hydroxy magnesium silicate（MgSi₂O₅（OH）₄）powder as the additives,and the optimum preparation conditions were explored.The corrosion resistance and micro-topography of these films were characterized.The main research contents and results are as follows:（1）The single factor experiment method has been employed to determine the optimum hydrolysis conditions of silane hydrolysis solution.The results show that:（1）the optimum hydrolysis conditions were determined to be that the KH-560 volume content is 3%,the methanol volume content is 20%,pH value is 4,hydrolysis temperature is 35 ℃ and hydrolysis time is 20-30 hours;（2）the optimum hydrolysis conditions were determined that the KH-570 volume content is 2%,the methanol volume content is 20%,pH value is 3,hydrolysis temperature is 40 ℃ and hydrolysis time is 5-15 hours;（3）the optimum hydrolysis conditions were determined to be that the KH-151 volume content is 2%,the methanol volume content is 20%,pH value is 3,hydrolysis temperature is 40 ℃ and hydrolysis time is 5-25 hours.（2）The orthogonal experiment method has been employed to determine the optimum preparation conditions of single silane film on surface of the cold-rolled steel.And corrosion parameters of these films were characterized by polarization curve and dropping corrosion experiment.And the optimum conditions of single silane film on surface of the cold-rolled steel were determined to be that the KH-570 volume content is 2%,the methanol volume content is 20%,pH value is 3,hydrolysis temperature is 40 ℃,dipping time is 3.5 min,curing temperature is 110 ℃,and curing time is 60 min.The silane film prepared under the best process conditions were compared with the bare cold-rolled steel.The results of polarization curves show that the icorr has a deeply decline from 6.778×10^-4 to 2.603×10^-6 A/cm².Dropping corrosion tests show the corrosion time is prolonged to 1168 s,compared with the 23 s of the bare cold-rolled steel.Electrochemical impedance spectroscopy（EIS）results also demonstrate that the corrosion resistance increases a lot.The surface morphology and chemical compositions of silane coated cold-rolled steel samples were characterized by scanning electron microscopy（SEM）and X-ray energy dispersive spectroscopy（EDS）.It can be concluded that cold-rolled steel samples are covered by uniform and rough silane film,causing that the scratches and holes on coldrolled steel disappear.Durability tests in 3.5wt% NaCl solution demonstrate that single silane film cannot offer a long-time corrosion resistance.（3）On the basis of the optimal processing conditions of single silane film,the cerium salt was added to the SCA hydrolysis solution to prepare composite silane films.Single factor experiment method has been employed to determine the optimum conditions of（NH₄）₂Ce（NO₃）₆,Ce（NO₃）₃·6H₂O and CeCl3.The results show that all three kinds of cerium salts can improve the corrosion resistance.When the（NH₄）₂Ce（NO₃）₆ added is 5 mg/L,the composite film has the highest corrosion resistance.The polarization curves show that the icorr decreases to 3.241×10^-7 A/cm².Dropping corrosion tests show that the corrosion time is prolonged to 3840 s.EIS spectra demonstrate that the corrosion resistance further increases,and durability tests in 3.5wt% NaCl solution demonstrate that cerium composite silane film shows self-healing capability,which can offer a long-time corrosion resistance.SEM-EDS results indicate that the film becomes more uniform and rough.（4）On the basis of the optimal processing conditions of single silane film,the fine particles were added to the SCA hydrolysis solution to prepare composite silane films.Single factor experiment method has been employed to determine the optimum conditions of serpentine and MgSi₂O₅（OH）₄ powder synthesized by a hydrothermal method.Based on the results,It can be concluded that both the serpentine and MgSi₂O₅（OH）₄ powders can improve the corrosion resistance.And the sample showing the best corrosion resistance contains 0.1 g/L serpentine.The polarization curves show that the icorr decreases to 6.268×10^-7 A/cm².Dropping corrosion tests show the corrosion time is enhanced to 3006 s.EIS spectra demonstrate that the corrosion resistance further increases.SEM-EDS results indicate that the serpentine powder is not uniform in the composite silane film..