Effect of Drawing Strain on the Microstructure and Properties of Zn-5Al Coated Steel Wire for Load Detection Cables

In order to further develop steel wires with high strength and corrosion resistance for ultra-deep oil well load detection cables，Zn-5Al alloy-coated steel wires were studied.The effects of cold drawing strain on microstructure， mechanical properties and corrosion resistance of coated steel wire were studied by means of scanning electron microscope， X-ray diffraction， electronic universal testing machine，electrochemical workstation and other instruments.Results showed that during the drawing process，the pearlite structure changed from equiaxed to fibrous along the drawing direction， with a gradual decrease in interlamellar spacing and a reduction in coating thickness.When the drawing strain exceeded 2.24， the tensile strength exceeded 2 400 MPa， meeting the requirements for steel wire used in the armoring of 10 000-meter oil well load detection cables.The results of dynamic polarization curves and full immersion tests showed that as the strain increased， the corrosion resistance of the Zn-5Al coated steel wire improved， and the corrosion rate decreased.The neutral salt spray corrosion test indicated that，in terms of long-term corrosion (506 h)， the best corrosion resistance was achieved with a strain value of 1.19， where the corrosion rate was 0.104 7 g/(m2∙h).The corrosion products mainly consisted of Zn6 Al2(OH)16 CO3 ∙4H2 O， Zn5(OH)8 Cl2 ∙H2 O， and small amounts of loose ZnO and Zn5(CO3)2(OH)6.After cold drawing deformation， the corrosion products became finer and denser， enhancing their protective effect on the substrate.Cold drawing deformation not only increased the strength of the steel wire but also effectively improved the corrosion resistance of the coated steel wire.