Construction And Corrosion Resistance Of Organometallic Complex Self-Assembled Conversion Film On Cold Rolled Steel Surface

Cold rolled steel is widely used in industry because of its high hardness and strength.But its chemical composition and structure make it vulnerable to corrosion.Therefore,the research on corrosion protection of cold rolled steel is very important.Conversion film technology is widely used in many corrosion protection technologies.Traditional phosphate conversion membranes and chromate passivation membranes have been gradually restricted due to environmental problems.In recent years,self-assembled conversion membranes have attracted more and more attention due to their green color and easy preparation.In this paper,organic ionic polymer and phytic acid colloids were selected to prepare conversion films on the surface of cold rolled steel,and the corrosion resistance and self-reinforcing properties were studied.Through the form of molecular self-assembly,the unsaturated functional groups contained in the molecules are used to complex with metal ions to form insoluble complexes on the surface of cold rolled steel,so as to block the contact between metals and corrosive substances and delay the occurrence of metal corrosion phenomenon.The main research results and experimental contents of this paper are as follows:(1)Preparation and corrosion resistance of PESA-Nd conversion film on cold rolled steel surface.The ionic polymer polyepoxide succinic acid(PESA)was selected as the organic film forming material,and the lanthanide metal neodymium was selected as the complex metal according to the properties of it.The carboxyl group in PESA was used to form an insoluble complex on the surface of cold rolled steel,and then the compact transformation film was formed by self-assembly.Metallographic microscope images show that conversion films have been successfully prepared on the surface of cold rolled steel substrate.The effects of different PESA content on film formation were investigated by EIS test.The results show that the corrosion resistance of the film decreases with the increase of PESA content.The reason is that with the increase of PESA content,the surface defects increase and the density of the film decreases.The XPS results showed that the PESA ratio in the membrane increased,while the content of metal ions decreased.It was found that when PESA and Nd were 1:1,the corrosion resistance of the film was the best.(2)Preparation and corrosion resistence of PAC-Zn conversion film on cold rolled steel surfacePhytic colloids were heated to form phytic colloids,and zinc ions were added into the solution.Phytic colloids and zinc ions were complexed on the surface of cold rolled steel to prepare PAC-Zn conversion films.Film forming time is an important factor affecting the performance of the film.When the film time is 3 min,the corrosion resistance of the film is the best.The film formation time of 3 minutes was immersed in 3.5 wt.%NaCl solution to explore its self-reinforcing properties.The research results show that PAC-Zn corrosion resistance of conversion film has since enhanced performance in in 3.5 wt.%NaCl solution,in 270 min of soaking time,|Z|f=0.01 Hz is on the rise.Through XPS test,the self-reinforcing mechanism can be speculated.With the progress of soaking,the complex bond of some phytic colloids and metal complexes in the membrane is broken,and the P-OH group in some phytic molecules is dissociated to P-O-,which is again complexed with metal ions in the solution,promoting the crack healing in the membrane and enhancing the density of the membrane.