Investigation Of The Preparation And Corrosion Resistance Of Zinc-aluminium Coated Steel Wires Forbridge Application

In this paper, based on a lot of relevant literatures and the actual situations in the factory, zinc-aluminum alloy coated steel wires were fabricated using galvanized double plating coating process in order to overcome the problem that the hot-dipping galvanized coated steel wires do not meet the requirements of corrosion resistance. The microstructure, mechanical properties and corrosion resistance of the zinc-aluminum alloy coated steel wires were investigated. The developed wires has been successfully used for the bridge cables.Preparation of the coating was studied. Based on the original galvanizing line and after the modification of the equipment, the control technology of the aluminum content, the reasonable line speed and the appropriate wiping technology were investigated. After a lot of preparation tests, a set of reasonable parameters were used for the Zn-Al coating preparation: 35 m/min line speed, oil carbon wiping of the Zn coating, nitrogen wiping of the Zn-Al coating and maintaining the content of Al ≥ 4.2% in the furnace. The surface quality of the Zn-Al alloy coating may meet the quality requirement.The microstructures of Zn-Al alloy coating, with different contents of aluminum, were observed by means of OM and SEM. It was found that the coating density was related to the content of aluminum. With the increase of aluminum content, the coating thickness increases, the coating microstructure was more homogeneous and the coating density was higher, XRD measurement indicates that the coating consists of mainly Zn and a few Zn-Al solution alloys. As the Fe-Al and Fe-Al-Zn contents were low, they were not detected by the XRD.The tensile tests of the Zn-Al alloy coated steel wires show that, the strength decrease is noly 3-5% after hot dipping. The tensile test results showed that the mechanical properties of the coated wires met the requirement of the related national standards. The mechanical properties of the Zn-Al alloy coated steel wires were even slightly higher than the galvanized steel wires. So they are suitable for bridge cables.In order to justify the corrosion resistance of the Zn-Al coated steel wire with different Al contents, the Electrochemical measurements, AC impedance analysis and neutral salt spray test were carried out. By comparing the zinc-aluminum alloy coated steel wires with galvanized steel wires, it was found that the corrosion resistance of Zn-Al alloy coated wires had a corrosion life more than two times higher than the pure zinc coated wires. The corrosion resistances of Zn-Al alloy coated wires increased with increasing content of aluminum. With higher aluminum content, the coating layer was more dense and homogeneous and thus has a better corrosion resistance. So the content of the aluminum content is the a key factor that affect the corrosion resistance of the Zn-Al coated wires.The zinc-aluminum alloy coated steel wire cables were successfully applied to the Irrigation River Bridge, the Miaozui Yangtze River Bridge and the Yalu Border River Highway Bridge. It is estimated that the wire cables exhibit a double servicing life compared to the Zn cable, which meet the demands of the customers.