| In order to improve the corrosion resistance of Q235 steel plate and improve the forming performance of coated steel plate,this subject designed and prepared coated steel plate with controllable thickness and structure on its surface.First,the Al-Cr composite coating was prepared on the surface of Q235 steel plate by electroplating composite hot-dip plating method,and then the Al-Cr composite coating was micro-deformed by the self-made surface micro-deformation device the study.The effects of electroplated Cr coating(Cr/Q235),hot-dip aluminizing process and micro-deformation process on the morphology,microstructure,corrosion resistance and formability of Al-Cr composite coating were studied.The main research content and conclusions are as follows:(1)The Al-Cr composite coating was prepared by electroplating and combining hot-dip coating method.The effects of chromium plating process and hot-dip aluminum coating process on the structure,phase composition,thickness and bonding strength of Al-Cr composite coating were studied.The results show that the wettability of liquid aluminum on the surface of Cr-coated steel plates is poor during hot dip aluminum plating.In order to improve the wettability of liquid aluminum,it was found the surface of the Al-Cr composite coating formed by 10%NH4Cl+27%ZnCl2 is smooth,with dense and uniform structure,and the coating quality is the best.As the immersion plating temperature is increased from 700℃ to 750℃ or the time is extended from 60s to 180s,the al-cr gradient composite coating changed from "three-layer structure"(the outer Al layer,the middle Al-Cr alloy layer and the inner Al-Cr-Fe alloy layer respectively)to "two-layer structure"(the outer Al layer and the inner Al-Cr-Fe alloy layer).In addition,with the increase of temperature,the thickness of the outer Al layer is reduced(from 37.17μm reduced to 12.68μm).With the extension of the immersion plating time,the thickness of the outer Al layer increased from 10.89 μm to 45.83 μm,and the thickness of the inner alloy layer increased from 22.24 μm to 67.48 μm.(2)The effects of the dip plating process and the surface micro-deformation process on the corrosion performance of the Al-Cr composite coated steel plate were studied.The results show that the corrosion resistance of Al-Cr composite coated steel sheet is significantly better than that of pure aluminum coated steel sheet and uncoated steel sheet.As the temperature of the dip plating increases,the corrosion resistance of the coated steel plate is enhanced.With the extension of the immersion plating time,the corrosion resistance of the coated steel plate decreases first and then increases.As the micro-deformation pressure increases,the corrosion resistance of the coated steel plate first increases and then decreases.The white corrosion pits appear on the surface of the soaked Al-Cr composite coating,and a large number of "honeycomb" corrosion holes are distributed in the pits,which can form channels with corrosion medium immersion with the micro cracks in the coating.After the surface is slightly deformed,the corrosion pits on the coating surface are significantly reduced,and the cross-section coating remains intact,and no obvious defects are generated,so that the corrosion resistance of the coating is improved.The corrosion products on the coating surface mainly include Al2O3,AlO(OH),Cr2O3.(3)The finite element simulation research method was used to evaluate the formability of the Al-Cr composite coated steel sheet.The deformation of the coated steel sheet during the drawing process and the effect of different processes on the formability of the coated steel sheet were studied.The results show that the convex corner of the Al-Cr composite coated steel plate with a diameter of 30 mm was cracked,and the flange area was wrinkled.The tendency of wrinkle in the flange area increases as the coating area increases.At the same time,the drawing depth of Al-Cr/Q235 increases with the increase of the sample diameter,And the maximum thickening rate appears in the flange area,and the maximum thinning rate appears in the corner area of the punch.Therefore,the maximum thickening rate increases first and then decreases with the increase of the sample diameter,but the maximum thinning rate increases with the sample increase in diameter.(4)The influence of sample diameter,coating thickness and surface micro-deformation on the drawing performance of Al-Cr composite coated steel plate was analyzed through deformation study,the maximum drawing force of the coated steel plate(11.71 kN increases to 17.81 kN)and the ultimate drawing force(13.23 kN increases to 18.25 kN)Increased,The results show that with the diameter of the Al-Cr-30/Q235 sample increases from 25mm to 30mm,the maximum and ultimate drawing forces of the coated steel plate increased from 11.71 kN to 17.81 kN and 13.23 kN to 18.25 kN,respectively.and there was no obvious crack on the surface of the drawn sample,only the local wrinkling and peeling of the coating.As the thickness of the coating increases,the fillet area of the punch of the deep-drawn specimen breaks,and the ultimate drawing force is reduced from 18.25 kN to 15.66 kN.After the surface micro-deformed Al-Cr composite coated steel sheet was deep-drawn,no cracking occurred,and the maximum and ultimate drawing forces increased.In this subject,an Al-Cr composite coating was prepared on the surface of Q235 steel plate by electroplating composite hot-dip plating.It effectively controlled the thickness and structure of the alloy layer.Aluminum coated steel plates with excellent corrosion resistance and formability are prepared,which lays a certain theoretical and practical foundation for the wider use of coated steel plates in the industrial field. |
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