Study On Preparation Of Al-Sc-Zr Wire By Cold-drawing And Heat-treatment

With the quick development of national economy,the domestic demand of electric power increases rapidly.Higher properties are requested for aluminum alloy wire.Aluminum alloy wire has a vast development space.Compared with developed countries,there is still a large disparity on the scientific research of aluminum alloy wire.In this thesis,the aluminum-scandium-zirconium alloys were designed.Al-Sc-Zr conductor was prepared by continuous rheo-extrusion process.Microstructure and Properties during the heat treatment were investigated.Aluminum alloy wire with different diameters were prepared by cold-drawing process.The following results are obtained.(1)The aluminum-scandium-zirconium alloys were designed.With the increase of Sc element content,the tensile strength of alloy aire increased and conductivity of alloy conductor decreased.The economic cost and comprehensive properties were comprehensively considered and the best of the alloy component should be Al-0.35Sc-0.2Zr(wt.%).(2)Effect of solution treatment on microstructure and properties of Al-0.35Sc-0.2Zr(wt.%)conductor was obtained.The tensile strength of alloy decreased and conductivity of alloy increased with the increase of solution time.The reason is that the average grain size increased,the precipitated phase dissolved into aluminum matrix and the dislocation density decreased with the increase of solution time.(3)Effect of aging treatment on microstructure and properties of Al-0.35Sc-0.2Zr(wt.%)conductor was obtained.During aging treatment,the grain morphology of alloy conductor did not change significantly and lots of secondary Al3(Sc,Zr)precipitates were separated out.The tensile strength and conductivity of alloy conductor increased at first and then tended to be stable with the increase of the aging time.This is because the size and content of precipitates increased with the increase of the aging time.The small and dispersed secondary Al3(Sc,Zr)precipitates can effectively pin dislocations and sub-grain,so the tensile strength of alloy conductor increased.When the aging time was 48 h,the size and content of precipitates stopped growth,and the tensile strength of alloy conductor then tended to be stable.The size and content of precipitates increased and the electronic scattering effect of precipitates enhanced with the increase of the aging time.So the conductivity of alloy conductor decreased.Sc and Zr dissolved in Al matrix constantly precipitated with the increase of aging time.The electronic scattering effect of the solute atoms gradually decreased.So the conductivity of alloy conductor increased.The analytic resulted show that the effect of the solute atoms played a major role and the conductivity of alloy conductor increased with the increase of the aging time.When the concentration of solute atoms was same,the electrical conductivity of alloy conductor decreased with the increase of the content and size of precipitates.(4)Effect of cold drawing on microstructure and properties of Al-0.35Sc-0.2Zr(wt%)conductor was obtained.The tensile strength increased and the elongation decreased with the increase of drawing pass.The tensile strength after heat-resistant test decreased with the increase of drawing pass.The conductivity of alloy conductor decreased with the increase of drawing pass.Declining scope of electrical conductivity is maintained at less than 1.0%IACS.This is because equiaxed grain was elongated with the increase of drawing pass,and the internal organization formed deformation bands in the drawing direction.With the increase of the dislocation and vacancy density,the electronic scattering effect enhanced.So the conductivity of alloy conductor decreased.(5)The different nominal diameter of 3 mm,3.56 mm,4.5 mm,5.46 mm,6.28 mm,7.56 mm,8.4 mm alloy conductor which had a significant improvement in the AT1,AT3 and AT4 standard of IEC 62004-2007" Thermal-resistant aluminum alloy wire for overhead line conductor" were prepared.The nominal diameter of 3mm Al-0.35Sc-0.2Zr(wt.%)conductor had the best comprehensive properties,and the tensile strength,elongation and conductivity were respectively 210.6 ± 1.47 MPa,7.57±1.38%and 60.11 ± 0.13%IACS.This was higher than the standard of IEC 62004-2007 "The tensile strength,elongation and conductivity were respectively 162 MPa,1.7%and 60%IACS".