Research On The Correlation Between The Characteristics Of The Zinc Bath And The Physical And Chemical Properties Of The Coating

The hot dip galvanizing is widely used in the field of heavy corrosion protection of the steel due to its excellent corrosion resistance.With the shortage of zinc resources and more stringent environmental requirements,the traditional hot dip galvanizing is no longer suitable for the needs of the times.It is inevitable to develop hot dip galvanized aluminum binary alloy,zinc aluminum magnesium ternary alloy and even complex metallic alloys.The purpose of this paper is to explore the intrinsic relationship between the characteristics of zinc bath and the physical and chemical properties of coatings,and to provide theoretical support for the composition design of hot dip galvanizing and the selection of experimental parameters..In this paper,the hot dip coatings of different compositions in the temperature range of 430⁴80?were immersed for 5 s,10 s,30 s,60 s,120 s,and the surface quality,thickness and microstructure of the coating were characterized by macro-scopic observation,electron microscopy and magnetic thickness measurement.And the influence of the characteristics of the zinc bath on the physical properties of the coating was obtained.At the same time,the electrochemical workstation and the salt spray chamber were used to test the corrosion resistance of the coating.The intrinsic connection between the protective ability of the coating and the characteristics of the zinc bath.?1?The change in surface tension and fluidity of the pure zinc bath does not cause leakage plating of the hot dip galvanized layer.When Al is added to the zinc bath,the fluxing agent partially fails,the plating layer is leak-deposited,the reduction of surface tension and the decrease of fluidity of zinc bath help to eliminate part of the leak plating.The Al content in the zinc bath is increased,and the plating is leaked.Rapid deterioration,the reduction of surface tension of zinc bath and the decrease of fluidity cannot improve the effect of Al.?2?The reduction of the surface tension of the zinc bath and the improvement of the fluidity can improve the gloss and flatness of the coating.However,when the surface tension of the zinc bath is too small,the zinc-iron reaction is too fast,and the difference in the thickness of the alloy layer is increased,the gloss and flatness of the coating are improved.At this time,the improvement of the fluidity of the zinc bath is unfavorable to the gloss and flatness of the coating.?3?The smaller the surface tension of zinc bath is,the more violent the reaction between zinc and iron is.The structure in the alloy layer grows sharply and melts back into the pure zinc layer of the coating,even into the zinc bath,which results in the adhesion of particles on the coating surface.The fluidity of zinc bath increases and the adhesion on the coating surface decreases.?4?The surface tension and fluidity of zinc bath can affect not only the thickness of alloy layer,but also the thickness of pure zinc layer.The smaller the surface tension of zinc bath is,the easier the zinc bath is to wet with the matrix,and the more intense the reaction between zinc and ferroalloy is.Therefore,the thickness of the alloy phase layer increases.With the increase of the fluidity of zinc bath,the amount of zinc adhering to the coating surface decreases,the pure zinc layer of the coating decreases and the thickness of the coating decreases.Al element in zinc bath not only affects the surface tension and fluidity of zinc bath,but also hinders the diffusion reaction of zinc and iron by forming Fe₂Al₅ phase.The more Al content in zinc bath,the more significant the hindrance effect of Fe₂Al₅ phase is,and the thinner the alloy layer is.Adding a small amount of RE element in zinc bath can make the alloy coating thicker,but when RE element is too much,the alloy coating will be thinner.?5?With the decrease of surface tension and the improvement of fluidity of zinc bath,the self-corrosion potential of the coating first increases and then decreases,and the self-corrosion current density first decreases and then increases,that is,the electrochemical performance of the coating first increases and then decreases.When the coating leaks out,the electrochemical performance of the coating deteriorates sharply.The more serious the coating leaks out,the worse its electrochemical ability.?6?When the Al content in the zinc bath is less than 0.05?4?,the smaller the surface tension of the zinc bath,the stronger the ability of the coating to resist neutral salt spray.When the Al content in the zinc bath is not less than 0.1?4?,the weakening of the fluidity of the zinc bath is beneficial to improve the resistance of the coating to neutral salt spray corrosion,and at this time,the surface of the plating layer is prone to leakage plating,and the more serious the leakage plating,the plating resistance.The more obvious the decline in corrosion capacity.Excessive Re element is easy to cause grain boundary corrosion and reduce the ability of the coating to resist neutral salt spray corrosion.?7?The immersion time does not affect the surface tension and fluidity of the zinc bath,but the immersion time can affect the resistance of the coating to neutral salt spray corrosion by affecting the surface quality and thickness of the coating..