Preparation And Evaluation Of Zinc-Aluminium-Magnesium-Cerium Coating Of Steel Wire For Bridge Cable

Hot-dip plating on steel wire is an effective means of steel wire corrosion prevention.With the development of the national economy and the construction of bridges,higher requirements have been placed on the overall performance and durability of bridge cables.Adding Mg element and a small amount of Ce element to Zn-Al alloy can improve the corrosion resistance of steel wire coating and extend the service life of bridge cable.In this paper,the Zn-5Al-1.5Mg-x Ce(x=0,0.05,0.10,0.25)coating for bridge cables was prepared by solvent plating,and the optimal hot dip plating process parameters were determined.Through SEM,EDS,XRD,neutral salt spray test,full immersion test,electrochemical test,etc.,the influence of Ce element content on the coating structure and corrosion resistance was studied.The corrosion behavior of the coatings in different kinds of corrosive media was studied.Meanwhile,the corrosion behavior before and after preloading was also studied,and the corrosion resistance mechanism of the coating was explored.The optimal process parameters of hot-dipping Zn-5Al-1.5Mg-x Ce(x=0,0.05,0.10,0.25)coating were determined through experiments.The results showed that the promotion flux composed of Zn Cl₂ 10-20%,NH₄Cl 5-15%,Sn Cl₂ 5-10%,KCl 3-6%,Ce Cl₃ 0.1-1%,CH₃OH 5-10%(wt.%),H₂O Bal.had the best effect on Zn-5Al-1.5Mg-x Ce(x=0,0.05,0.10,0.25)coating.Auxiliary plating at 80?for 3min,and hot-dip plating in plating solution at 450?for about 30s after drying,the coatings with uniform,leak-free plating and good surface quality was obtained,and the hot-dip steel wires remained excellent mechanical properties.The effect of Ce element content on the micro-morphology and micro-structure of Zn-Al-Mg-Ce alloy coating was studied.The results showed that the morphology of the Zn-5Al-1.5Mg-x Ce(x=0,0.05,0.10,0.25)coating is about the same.The coating structure was composed of Zn-rich phase,Al-rich phase and Zn/Al/Mg Zn₂(or Mg₂Zn₁₁)ternary eutectic structure.The addition of a small amount of Ce element can increase the proportion of the ternary eutectic structure of the coating.Ce element can thin the plating layer,refine the Al-rich phase,and improve the uniformity of the plating layer.When Ce element is added in an amount of 0.10 wt.%,the thinning effect is the best.The effects of Mg and Ce elements on the corrosion resistance of the coating were studied.The results indicated that the corrosion resistance of the coating can be improved by adding Mg element and a small amount of Ce element.The corrosion resistance of Zn-5Al-1.5Mg-0.10Ce alloy coating was the best,about 5 times that of the Zn-5Al alloy coating.Mg element inhibited the transformation of corrosion products from Zn(OH)₂ to Zn O which was loose and porous,and promoted the formation of protective corrosion products Zn₅(OH)₈Cl₂·H₂O;Ce element improved the uniformity of the coating,reduced local corrosion,and improved the uniformity and compactness of the protective layer of the corrosion products,thereby improving the corrosion resistance of the coating.The corrosion behavior of the coatings in different kinds of corrosive media was studied.The results implied that the corrosion resistance of the different coatings in Na Cl solution,Na₂SO₄ solution and dilute H₂SO₄ solution changed uniformly.The corrosion resistance of the coating was best for Zn-5Al-1.5Mg-0.10Ce,followed by Zn-5Al-1.5Mg,and Zn-5Al the worst.The addition of Mg and Ce elements can greatly improve the corrosion resistance of the coating in Na Cl solution and Na₂SO₄ solution.The corrosion resistance of the Zn-5Al-1.5Mg-0.10Ce coating was about 4 times that of the Zn-5Al coating in Na Cl solution and Na₂SO₄ solution.The Mg element and Ce element had relatively small improvement of corrosion resistance in dilute H₂SO₄solution.The corrosion behavior of steel wire coating after tensile stress was studied.The results show that the tensile stress will shorten the service life of the hot-dip steel wire coating.After applying 40%?_s tensile stress to the hot dip Zn-5Al-1.5Mg-0.10Ce alloy coated steel wire,defects such as cracks will no longer occur in the coating,which can play a good role in isolating and protecting the steel wire matrix and reducing the effect of stress on the service life of steel wire coating.