Performance Control And Process Optimization Of Al-Zr And Al-Mg-Si-Sc Alloys

In addition to good mechanical properties,aluminum alloys also have high electrical conductivity,often used as electrical materials.Compared with copper conductor materials,aluminum alloy wire materials are more and more used due to their low density,light weight,and low price.For example,the wires used in overhead power transmission lines,automobile battery wires and harness original wires,high-voltage isolation switch,etc.However,the strength of pure aluminum is very low,and it is difficult to obtain practical applications.Various strengthening methods,such as solid solution strengthening,work hardening,fine grain strengthening,and precipitation strengthening,all increase defects(including point defects,line defects,and the density of surface defects),while hindering the movement of dislocations,also has a strong scattering effect on the movement of electrons,leading to a decrease in conductivity.This mutually exclusive relationship between strength and conductance makes it difficult to have both high strength and high conductivity,and thus has become a bottleneck restricting the high-performance development of new aluminum wire materials.In this paper,Al-Zr and Al-Mg-Si-Sc aluminum alloy are studied respectively.The multilayer microstructure of the material is systematically characterized,which is related to the mechanical and electrical properties.Fully understand the dominant characteristics of the microstructure that depend on performance,so as to optimize the composition or processing/heat treatment process to achieve the design of the microstructure and further improve the mechanical/electrical performance.In the study of the Al-Zr series,the effects of processing deformation and aging treatment on the microstructure and properties of the alloy at different Zr contents(0.05,0.15,and 0.25 wt%)were studied.On this basis,wire process was optimized.The results show that:(i)as the Zr content increases,the hardness of the alloy in the as-cast condition increases,and the electrical conductivity decreases;(ii)as the amount of deformation increases,the hardness of the alloy increases,and the electrical conductivity decreases slightly;(iii)The impact of aging processing is related to the time period of the process.When aging directly at the as-cast state,aging needs to be performed at a higher temperature.At the same aging temperature,the higher the Zr content,the higher the hardness of the alloy after aging and the lower the electrical conductivity.If the aging is performed after rolling deformation,the density of defects such as dislocations in the deformed alloy increases,the Zr diffusion coefficient increases,and the aging temperature can be performed at a lower temperature.However,for the wires made after rolling and drawing,defects such as dislocations are preferentially restored to reduce the defect density,and the properties of the alloy obtained by aging under the state of the wire are poor.The optimized preparation process of the wire is:aging after as-cast rolling,and then cold drawing into the wire,so as to obtain the optimal microstructure of the ultrafine crystal grains+nano-coherent precipitation phase particles in the crystal grains.Simultaneously increases strength and conductivity.For Al-0.05wt%Zr and Al-0.15wt%Zr alloy wires with lower Zr content,the comprehensive properties of the obtained wires are better when the aging temperature is 265? after rolling.For an Al-0.25wt%Zr alloy wire with a higher Zr content,when the aging temperature is 350? after rolling,the overall performance of the obtained wire is better.In the study of Al-Mg-Si-Sc alloy,comparisons were made between different Mg/Si ratios and different grain sizes(coarse grains vs ultrafine grains).The results show that:(i)?"precipitated phase and precipitation strengthening within the grains of coarse-grained Al-Mg-Si-Sc alloy strongly depend on the Mg/Si ratio,and the conductivity is less affected by the Mg/Si ratio.Excessive Si(Mg/Si ratio<1.73)will promote the precipitation of ?" phase,and the number of precipitated phases is significantly larger than that of Mg excess(Mg/Si ratio>1.73);(ii)The Si excess alloy exhibits higher electrical conductivity than the Mg excess alloy.Aging softening occurs in superfine-grained alloys with excessive Si during aging,while the hardness of the ultrafine-grained alloys with excessive Mg remains substantially unchanged during aging;(iii)The optimized preparation process is cast-rolling+aging(? Aging 200?)+drawing,the wire material prepared under this process has high tensile strength and electrical conductivity,and the best overall performance,of which Mg excess and Si excess alloys show the maximum tensile strength and electrical conductivity,respectively.The research results in this article are helpful for understanding the relationship between the composition-process-structure-property of aluminum alloy wire materials,and can provide a reference for the development of high-performance aluminum alloy wire.