Study On The Preparation And Properties Of Zinc-Aluminium-Magnesium Coating In Ultra- High Strength Steel Wires

To improve the corrosion resistance of bridge cable wire,a new type of Zn-Al-Mg alloyed coating is prepared by solvent method,and the fabrication process and the influence of Mg on the microstructure and properties of Zn-Al-Mg alloyed coating was studied by using Scanning Electron Microscope?SEM?,X-ray Diffraction?XRD?.The mechanism on corrosion resistance for Zn-Al-Mg alloyed coating was discussed.The fabrication process of Zn-Al-Mg alloyed coating was studied.The results show that the flux with the composition of NH₄Cl:ZnCl₂:SnCl₂:CeCl₃:H₂O=?80-100?:?100-120?:?70-90?:?1-5?:?685-749?have the best effect on Zn-5Al-?0.5¹.5?Mg alloyed coating.The best process temperature is 60-80?,and optimum process time is 90s and dipping at 450°C for 60s,the Zn-Al-Mg alloyed coating with no-skip plating,good surface brightness and uniform thickness is obtained.The influence of Mg on microstructure and mechanical properties of Zn-Al-Mg alloyed coating was studied.The results show that when the content of Mg is 0.5%,the alloyed coating is composed of Zn-rich phase and Al-rich phase.With the increase of Mg,the microstructure of coating is composed of Al-rich phase,Zn-rich phase and ternary eutectic phase?Zn/AlMgZn₂?,and the hardness is also obviously increased.When the content of Mg is 1.5%,the hardness of the alloy coating reach 127.9HV,which is 57.9 higher than Zn-5Al coating.The influence of Mg on corrosion resistance of Zn-Al-Mg alloyed coating was investigated.Under the same conditions,the addition of Mg can reduce the corrosion rate.The corrosion resistance of Zn-5Al-1.5Mg alloyed coating is best,which is about 2.4 times that of Zn-5Al alloyed coating and 3.9 times that of Zn coating.The improvement of corrosion resistance is related to the change of corrosion products:the addition of Mg inhibits the conversion of corrosion products to ZnO and promotes the formation of Zn₅?OH?₈Cl₂·H₂O.The effect of tensile stress on properties of Zn-Al-Mg alloyed coating was investigated.Compared with the Zn coating,there is not crack on Zn-Al-Mg alloyed coating by loading tensile stress(40%_?7?,which ensures the continuity of coating.However,there is crack on the surface of Zn-Al-Mg alloyed coating due to stress loading,which can increase the corrosion rate and accelerate the corrosion.