Fabrication And Properties Of Al-Fe-Cu-RE-Zr Alloy Conductors For Medium And Low Voltage Cables

Al-Fe-Cu alloys have good electrical conductivity,strength,plasticity,corrosion resistance and creep resistance.They are mainly used in low and medium voltage wires and cables.In order to meet the needs of urbanization construction,capacity enhancement,energy saving and emission reduction,a new type of medium strength and high conductivity aluminum alloy single wire was developed on the basis of traditional Al-Fe-Cu alloy.The mechanical properties of the alloy were further improved and its comprehensive properties were better on the premise of ensuring high conductivity.On the basis of Al-Fe-Cu alloys,adjusting the content of Fe and Cu elements,and adding RE and Zr elements,the effects of element content on Electrical and mechanical properties of Al-Fe-Cu alloys have been studied by means of metallographic observation,scanning electron microscopy,energy spectrum analysis,X-ray diffraction analysis,differential thermal analysis,tensile test,hardness test and resistivity test.The composition of Al-Fe-Cu-RE-Zr alloy was optimized by orthogonal test,and the as-cast structure and phase composition of the alloy were observed and analyzed.In addition,the effects of homogenization annealing,extrusion process and finished product annealing on the structure and properties of the alloy have been studied.Finally,the preparation process of medium-strength and high-conductivity Al-Fe-Cu-RE-Zr single-wire was determined.The main results are as follows:(1)The influence degree of each element on the tensile strength of the alloy from strong to weak is:Fe>RE>Cu>Zr,and the effect of Fe content on the tensile strength is very significant.The influence degree of each element on the conductivity of the alloy from strong to weak is:Zr>RE>Fe>Cu,in which the content of Zr element has a significant effect on the conductivity,and the content of RE element has a significant effect on the conductivity.The influence degree of each element on elongation of the alloy from strong to weak is:RE>Cu>Zr>Fe,and the content of RE element has a significant effect on elongation.(2)Through comprehensive evaluation of electrical conductivity,tensile strength and elongation of annealed aluminium alloy,the optimum composition of the alloy is determined as follows:Al-0.5Fe-0.25Cu-0.3RE-0.05Zr,and its electrical conductivity,tensile strength and elongation are 61.8%IACS,99 MPa and 24.6%respectively.The as-cast microstructures of the optimum alloy are mainly equiaxed grains with segregation at grain boundaries.The morphologies of the phases are spherical,punctate,acicular and short rod-like.The spherical and short rod phases are mainly rare earth phases,which a large amount of Cu segregation occurs near.A small amount of Al3Zr phase is also found near rare earth phases.The point and needle phases are mainly Al-Fe-(Cu)phase,mainly Al6Fe binary phase and Al7Cu2Fe ternary phase.(3)The as-cast Al-0.5Fe-0.25Cu-0.3RE-0.05Zr alloy was homogenized by different homogenization systems.With the increase of temperature or holding time,the dendrite segregation in the alloy was eliminated,the non-equilibrium eutectic structure gradually disappeared,the second phase matrix near the grain boundary was refined,the grain boundary changed from continuous distribution to intermittent distribution,and the homogenization degree increased.The optimum homogenization system is holding for 16 hours at 520 ?.The diffusion of Cu element plays a dominant role in the homogenization process of as-cast alloys.The homogenization kinetics equation of the alloys is obtained.The equation is good to verify the optimum homogenization system(520 ?� 16h).(4)The dynamic recovery of Al-0.5Fe-0.25Cu-0.3RE-0.05Zr alloy occurs mainly during hot extrusion at 350 ?.The recrystallized grain of as-annealed alloys cooled by water during hot extrusion,which has higher tensile strength,no obvious decrease in conductivity and the best comprehensive properties,is finer than air-cooled alloys.The recrystallization incubation period of as-drawn alloy wires cooled by water becomes longer during the annealing of isothermal finished products at the same temperature,and the recrystallization is not easy to occur.The recrystallization activation energy of as-drawn alloy after water cooling is 112.3KJ/mol,which is about 22%higher than that of as-drawn alloy after air cooling.(5)The annealing process of the as-drawn Al-0.5Fe-0.25Cu-0.3RE-0.05Zr alloy is determined to be 300 ? � 2h.Under this condition,the comprehensive properties of the alloy reached the best,with its tensile strength 113.3MPa,elongation 15.1%and conductivity 62.0%IACS.