Investigations On The Strength-electrical Conductivity Relation And The Degradation Mechanism Of Overhead Aluminum Conductor

Power grid is the "lifeblood" of economic and social development.Overhead transmission line is an important infrastructure for long-distance power transmission.Overhead transmission line is an essential carrier of power transmission,and aluminum wire is an important component of overhead transmission.The overhead line is usually serviced in the state of external load.Once the load is greater than the tensile strength of the overhead line,may its failure occur,resulting in huge economic losses.Therefore,high strength ensures the safety and reliability of transmission lines.In addition,during the process of power transmission,the line loss of overhead wires will cause the consumption of electric energy.High electrical conductivity can reduce the line loss in the process of power transmission,reducing the coal consumption of thermal power plants and achieving energy conservation and emission reduction.To reduce the loss of electric energy during the process of power transmission,the conducting metallic materials with high electrical conductivity are usually chosen as the overhead conductor.Considering the properties and economic benefits of the materials,aluminum or aluminum alloy wires are used as the conducting materials for the aluminum conductor steel reinforced,all aluminum alloy conductor and aluminum conductor aluminum alloy reinforced.Improving the strength and electrical conductivity of aluminum wire is an important scientific and industrial problem in the field of overhead transmission.Grain is an important microstructure of aluminum wire for overhead transmission.Besides,the evolution of grains is closely related to the strength and electrical conductivity of aluminum wire.The refinement of grains could lead to the grain boundary(GB)strengthening effect,but it will increase the density of GBs and the scattering of electrons,which will damage the electrical conductivity of aluminum wire.Therefore,it is difficult to optimize the relationship between the strength and the electrical conductivity by controlling the grain size.Previous studies have shown that the relationship between strength and electrical conductivity can be improved by adjusting the shape and size of grains and introducing elongated grains parallel to the direction of electron motion.However,the previous studies are mostly based on qualitative descriptions.It is of great significance to establish the quantitative relationship between grain,strength and electrical conductivity for the microstructural design of high strength and high electrical conductivity aluminum wires.In this study,the resistivity of vertical and parallel GBs is calculated quantitatively.In addition,the resistivity coefficient of parallel GB is defined,which represents the ratio of the resistivity of parallel GB to that of vertical GB.For the commercially pure Al wire(CPAW)in this paper,the resistivity coefficient of parallel GB is between 0.38 and 0.92,indicating that the resistivity of parallel GB is smaller than that of vertical GB.In addition,the resistivity coefficient of parallel GB decreases with the increase of grain length-to-diameter ratio.In this work,the influence of grain evolution(e.g.,length-to-diameter ratio and grain volume)on the relationship between strength and electrical conductivity is quantitatively revealed by comparing and analyzing the CPAW deformed at different strain amounts.When the grain volume remains unchanged and the length-to-diameter ratio increases,the strength and electrical conductivity of CPAW can be improved simultaneously,which provides a potential method to optimize the relationship between strength and electrical conductivity of aluminum wire.The thermal effect commonly exists during the process of transmission due to the interaction between the resistance of overhead conductor and current.As a result,it is of great significance to study the micro structure and properties of aluminum wire under different heat treatment conditions.At present,there is little research on the evolution of the relationship between strength and electrical conductivity of annealed aluminum and aluminum alloy.To simulate the thermal environment of aluminum wire in actual service,the CPAW and Al-Fe alloy wire(AFW)are taken as the research object in this work.The annealing treatments of CPAW and AFW are carried out at different temperatures.It is found that the strength and electrical conductivity of the annealed aluminum wire exhibit a linear trade-off relation.The microstructural observations demonstrate that the relationship between strength and electrical conductivity of CPAW and AFW is closely related to the grain width and GB type transformation.In addition,when the yield strength of the annealed AFW is the same as that of the annealed CPAW,the electrical conductivity of the CPAW is always higher.Furthermore,the slope of linear relationship between strength and electrical conductivity of the annealed AFW is smaller than that of the annealed CPAW.By comparing the relationship between strength and electrical conductivity and the microstructural evolution of annealed CPAW and AFW,it is found that the difference between the relationship between strength and electrical conductivity of annealed CPAW and AFW results mainly from the difference in grain length and the effect of precipitates,which provides a theoretical basis for the preparation of anti-aging aluminum wire.