The Effect Of Si On Microstructure And Properties Of Zn-5Al And Study On The Zn-Al-Mg Hot-dip Galvanized Coated Steel Wires For Bridge Cables

With the development of bridge engineering,the requirements of the mechanical properties and corrosion resistance of the steel wire which used for bridge cable are increased.Because of traditional hot dip galvanized aluminum layer can not meet the tensile strength and corrosion resistance of modern bridges steel wire,based on referring to a lots of foreign literature in this article,the effect of different content of silicon elements in steel wire and different content of silicon in Zn-Al bath on the microstructure and properties of Zn-5Al alloy coated steel wire was studied.In addition,in order to improve the performance of the steel wire,Zn/Zn-Al-Mg and ZnAl/Zn-Al-Mg composite coatings were prepared by double plating method in this paper,and their microstructure and properties were analyzed to provide reference for the industrial application of bridge cable steel wire.The microstructure of the alloy coatings obtained on the steel wire with different Si contents were studied by SEM It was found that the thickness of the Fe-Al phase layer decreased with the increase of the content of Si,and the microstructure changed from the duplex structure Fe₂Al₅-Fe Al₃to the Fe Al₃structure.The coating of steel wire with Si content of 0.91%has better corrosion resistance,but its adhesion to the substrate is poor,and the surface will appear peeling and cracking in the wrapping test.The addition of Si was not decrease the tensile strength of steel wire significantly.The microstructure of the cross section of coating changed,and many Al-rich black blocks appeared in the coating.In addition,the addition of Si elements can improve the electrochemical performance and corrosion resistance of the alloy coating,but it can not change the type of corrosion products.It was affect the relative content of various corrosion products to improve their corrosion resistance.The copper accelerated salt spray test showed that after Si element was added in the alloy coating,coating would be corroded 5 days later than the traditional Zn-Al alloy coating,and then the surface would be corroded completely.Combination with the results of electrochemical test,the addition of 0.1%Si content shows the best corrosion resistance,and its corrosion resistance is 1.5 times more than tranditional Zn-5Al coating.Zn/Zn-Al-Mg and ZnAl/Zn-Al-Mg coatings were prepared by double plating.It was found that the addition of Mg element would improve the quality and uniformity of the alloy coating,and the outer layer of the coating would form a ternary eutectic of Zn/Al/Mg Zn2 phase,which would refine the structure of the coating.Therefore,the two kind of coatings would have better tensile properties.On the other hand,the surface of the two composite coatings will be covered with dense and uniform corrosion products after corrosion,preventing further corrosion.The ZnAl/Zn-Al-Mg alloy coating shows better corrosion resistance because of the high Al content in the alloy coating,and its corrosion resistance is 2.5 times more than tranditional Zn-5Al coating.However,the Fe-Al phase layer of the ZnAl/Zn-Al-Mg alloy coating is thinner and discontinuous,and the surface would peel after the wrapping test.