Effect Of Deformation Method And Low Temperature Aging On Strength And Conductivity Of 6201 Aluminum Alloy With High Mg、Si Content

6xxx series Al-Mg-Si alloy is widely used in the field of high-voltage overhead transmission lines because of its lightweight,excellent corrosion resistance,electrical conductivity and mechanical properties as well as long service life,abundant reserves and ease of manufacture.The purpose of this paper is to solve the contradiction between strength and conductivity of 6201aluminum alloy by microstructure and properties modification in terms of alloy composition,deformation modes and heat treatment process,and to provide theoretical and practical guideline for the production of new high strength,high conductivity lightweight aluminum alloy wire material.In this paper,6201 aluminum alloy with high Mg and Si levels（Al-0.81Mg-0.79Si）was prepared by the conventional gravity casting.The microstructural evolution,mechanical properties and electrical conductivity of the as-cast,solid-solution,rolled,Equal channel angular pressing（ECAP）processed,ECAP-rolled and aged alloys were investigated.The main results are as follows.（1）As-cast Al-0.81Mg-0.79Si alloy is composed ofα-Al,Mg₂Si,and a small amount of Al-Fe-Si impurity phase.After solution treatment at 550℃×1 h,a large number of Mg₂Si particles dissolved in the matrix and the grain size ofα-Al matrix remained almost unchanged.The electrical conductivity of the alloy decreased sharply from 47.2%IACS to 42.6%IACS because a large number of solute atoms dissolved in the matrix resulted in lattice distortion.On the contrary,the hardness of the alloy increased from 69.7 HV to 84.8 HV,the tensile strength increased from 151.71 MPa to 181.84 MPa,and the elongation increased from 5.38%to 10.55%.（2）Rolling produces defects such as high-density dislocations and non-equilibrium vacancies,which induces the dynamic precipitation of a large number of fine Mg₂Si phases,and theα-Al grains are significantly elongated.The combination of strain strengthening,precipitation strengthening and electron scattering caused by defects led to a sharp increase in hardness of the rolled alloy with a reduction of 41%to 115.4 HV,a decrease in electrical conductivity to 41.5%IACS,a sharp increase in hardness of the rolled alloy with a reduction of 82.6%to 125.3 HV and a decrease in electrical conductivity to 42.1%IACS.（3）After low temperature aging at 130℃×8/16/24/32/40/48 h,the conductivity of the rolled alloy increases continuously with the extension of the aging time.The rolled alloy with a reduction of 41%undergoes aging at 130℃×48 h,and the peak electrical conductivity reaches 44.9%IACS.The rolled alloy with a reduction of 82.6%undergoes aging at 130℃×48 h,and the peak electrical conductivity reaches 44.9%IACS.The rolled alloy with a reduction of 41%undergoes aging at 130℃×16 h,and the peak hardness reaches 116.5HV.The rolled alloy with a reduction of 82.6%undergoes aging at 130℃×8 h,and the peak hardness reaches 129.4 HV.After artificial aging at 130℃×48 h,the comprehensive properties of the rolled alloy with 82.6%reduction are the best.The Vickers hardness is 118.2 HV,the tensile strength is 335.39 MPa,the elongation is 6.11%,and the conductivity reaches 48.4%IACS.（4）After the solid solution alloy undergoes one-pass ECAP at 200℃,theα-Al matrix grains are significantly reduced and refined,and at the same time,there are highly dense Mg₂Si nano-precipitated phases along the grain boundaries,sub-grain boundaries,high-density dislocation and other defects are evenly precipitated.The hardness of the as-ECAPed alloy increased significantly from 84.8 HV of the solid-solution alloy to 104.6 HV,an increase of 23.3%;the conductivity also increased significantly,from 42.6%IACS to50.9%IACS,an increase of 19.5%.After the low-temperature aging at 130℃×24/32/40/48 h,the Vickers hardness of the as-ECAPed alloy reached a peak value of 118.1 HV at 24 hours of aging,then decreased significantly,and finally remained almost unchanged,while the conductivity of the alloy increased continuously and reached a peak value of 52.7%IACS at 48 h.After low temperature artificial aging at 130℃×48 h,the comprehensive properties of the alloy are the best.The Vickers hardness is 113.9 HV,the tensile strength is297.9 MPa,the elongation is 4.63%,and the conductivity reaches 52.7%IACS.（5）The as-ECAPed alloy was rolled with a reduction of 81.2%.The hardness of the alloy was 115.4 HV,the tensile strength was 303.50 MPa,the elongation was 4.10%,and the conductivity was 50.6%IACS.After low temperature aging at 130℃×24/32/40/48 h,the hardness of the alloy reached the peak value at 24 h,which was 109.7 HV,and the conductivity reached the peak value at 48 h,which was 54.1%IACS.After 81.2%reduction rolling and130℃×40 h low temperature artificial aging,the comprehensive properties of the as-ECAPed alloy are the best.The Vickers hardness is 107.7 HV,the tensile strength is 309.31 MPa,the elongation is 5.73%,and the conductivity reaches53.9%IACS.