Study On Electrodeposition Of Zn-Fe Alloy In Deep Eutectic Solvent

Due to the excellent mechanical property and corrosion resistance,Zn-Fe alloy has been considered as an ideal substitute for chromium coating and has been widely applied in automobile,machinery and aerospace fields.At present,the electrodeposition of Zn-Fe alloy is mainly carried out in aqueous solution.However,the electrodeposition of zinc-ferroalloy in aqueous solution has some problems,such as hydrogen embrittlement,complex process and difficult solution treatment after plating,which seriously affects the properties of Zn-Fe alloy.Deep eutectic solvent has the advantages of wide electrochemical window,high conductivity and good thermal stability.In addition,deep eutectic solvent synthesis raw materials are cheap,green and non-toxic,and can exist stably in the air.Therefore,deep eutectic solvent is considered as an ideal solvent for electrodeposition of Zn-Fe alloy.In this research,choline chloride and ethylene glycol（mole ratio:1:2）were used as raw materials to prepare deep eutectic solvent.Zinc chloride and ferrous sulfate were used as main salts to electrodeposit Zn-Fe alloy by constant current method.This paper studied the electrochemical behavior and electrocrystallization process of zinc and iron in deep eutectic solvent.This paper also investigated the effects of process parameters and additives on the morphology,crystal structure,corrosion resistance,microhardness and friction resistance of the coating.The main work content includes:（1）Deep eutectic solvent can chelate zinc ions and ferrous ions,reduce the deposition potential difference between them,and promote the co-deposition of zinc and iron.Zinc and iron tend to nucleate in three dimensional instantaneous mode in deep eutectic solvents.The optimum process parameters were determined by control variable method:zinc chloride concentration is 14.0 g·L^-1,ferrous sulfate concentration is 2.0 g·L^-1,current density is 200 mA·cm^-2,temperature is 80℃and deposition time is 1 h.（2）This paper studied the effects of water content on electrodeposition of Zn-Fe alloy in deep eutectic solvent.Water can reduce the viscosity of deep eutectic solvent,improve the conductivity and increase the grain size of the coating.When the water content is 4wt.%,deep eutectic solvent can maintain the original electrochemical window,and the prepared coating is smooth and compact,shows the best corrosion resistance in 3.5%sodium chloride solution.（3）This paper studied the effects of benzoguanidine on electrodeposition of Zn-Fe alloy in deep eutectic solvent.The results show that:（1）The nitrogen atom in benzoguanidine provides electrons to the vacant orbital of zinc atom and iron atom,and benzoguanidine adsorbs on the coating surface.（2）With the increase of benzoguanidine concentration,the electrodeposition speed decreases,the coating from triangular cone structure into a package structure.（3）The coating is composed of face-centered cubic Fe₃Zn₁₀,and the optimal crystal plane is（400）.With the increase of benzoguanidine concentration,the average grain size is refined.（4）Benzoguanidine improves the corrosion resistance of the coating.When the concentration of benzoguanidine is 0.15 g·L^-1,the corrosion potential of the coating is the most positive,the corrosion current density is the least,the polarization resistance and charge transfer resistance is the largest,and the corrosion resistance is the best.（5）With the increase of the concentration of benzoguanidine,the hardness and friction resistance of the coating are improved.（4）This paper studied the effects of dimethyl sulfoxide on electrodeposition of Zn-Fe alloy in deep eutectic solvent.The results show that:（1）The oxygen and sulfur atoms on dimethyl sulfoxide provide electrons to the vacant orbitals of zinc and iron atoms,and dimethyl sulfoxide adsorbs on the surface of the coating.（2）With the increase of dimethyl sulfoxide concentration,the electrodeposition speed decreases and the coating structure changes from triangular cone to encapsulation.（3）The coating is composed of face-centered cubic Fe₃Zn₁₀,and the optimal crystal plane is（400）.With the increase of benzoguanidine concentration,the average grain size is refined.（4）Dimethyl sulfoxide improves the corrosion resistance of the coating.When the concentration of dimethyl sulphoxide is 2.0 g·L^-1,the corrosion potential of the coating is the most positive,the corrosion current density is the least,the polarization resistance and charge transfer resistance are the largest,and the corrosion resistance is the best.（5）With the increase of dimethyl sulfoxide concentration,the hardness and friction resistance of the coating are improved.