Effects Of Si/Ca Master Alloys On Microstructure And Properties Of High-Strength And High-Conductivity 6201 Aluminum Alloys

With the rapid development of the economy,the increase in power demand and the continuous expansion of the power grid,the line power load continues to increase,and the power transmission capacity requirements continue to increase.At present,the high-strength and high-conductivity 6201 all-aluminum alloy wire materials commonly used can no longer meet the needs of power development.This paper solves the contradiction between the strength,conductivity and high temperature resistance of the 6201 aluminum alloy from the aspects of alloy composition,structural design and preparation method,and develops a new high-strength,high-conductivity lightweight low-cost aluminum alloy wire material.It has important theoretical research and engineering practical significance to meet the demand of long-distance,large-span overhead transmission lines for all-aluminum alloy stranded wires and reduce the power loss of transmission lines.In this paper,Si/Ca master alloys were used to investigate the effects of Si and Ca addition methods on the properties of 6201 aluminum alloy.The effects of Si addition on the properties of as-cast 6201 aluminum alloy were investigated using pure Si and Al-12Si master alloys.The effects of Ca addition on the microstructure,mechanical properties and electrical conductivity of as-cast,solid solution and post-extrude aged of 6201 aluminum alloy were investigated by using 0Ca,Mg-8Al-18Ca,Mg-10Al-27Ca and Mg-30Ca master alloy.The master alloy is prepared by magnetic suspension smelting.The 6201 aluminum alloy is prepared by ordinary gravity casting method.The treatment process includes solution treatment,equal channel angular pressing and artificial aging.The main research results are as follows:（1）The effect of Si addition on the properties of the alloy is clearly different.Compared with pure Si addition,the Al-12Si near-eutectic intermediate alloy addition method promotes the precipitation of nano-scale Mg₂Si particle phase in the aluminum matrix crystal and grain boundary,and significantly refines the long strip-shaped Al₈Fe₂Si phase at the grain boundary to short.Rod shape and increase its volume fraction.Therefore,the Al-12Si addition alloy significantly increases the yield and tensile strength of the as-cast alloy by 130 MPa and 194 MPa on the basis of slightly increasing the electrical conductivity,and the strength of the alloy added by pure Si is increased by 28.3%and 64.14%,respectively.Maintain excellent plasticity and elongation of 17.7%.（2）The same second phase was found in the three 6201 aluminum alloys with different Ca-containing master alloys:Al₈Fe₂Si phase,Mg₂Si phase and CaSi₂ phase.In the control group without Ca addition,only Al₈Fe₂Si phase and Mg₂Si phase were found.Among them,Mg-8Al-18Ca containing more Mg can promote the precipitation of Mg₂Si phase,and Mg-10Al-27Ca can promote the precipitation of CaSi₂ phase.It should be noted that since the composition design does not involve the Fe element,the Fe element present is introduced as an impurity,and the element is difficult to avoid.（3）The addition of different Ca intermediate alloys significantly affects the mechanical properties of as-cast alloys.The alloys with Mg-8Al-18Ca added in the as-cast state have the highest tensile strength and yield strength,respectively133.4 MPa and 195 MPa,but the lowest elongation is 10.4%;the comprehensive mechanical properties of the alloy with Mg-10Al-27Ca added preferably,the tensile strength,yield strength and elongation after fracture are 121.2 MPa,184MPa and 13.2%,respectively;the mechanical properties of the alloys with 0Ca and Mg-30Ca are close,the tensile strength and yield strength are lower,but the elongation higher.（4）The effect of solution treatment on the mechanical properties and electrical conductivity of aluminum alloys with different Ca intermediate alloy addition methods is significant.After solution treatment,some of atoms dissolve into the matrix,which causes the size of the second phase to become smaller,causing lattice distortion,which improves the deformation resistance of the alloy and the scattering of electrons.Therefore,compared with the as-cast state,the mechanical properties of the four alloys rise but the conductivity reduce.（5）Strong plastic deformation and aging after extrusion significantly improve the mechanical properties and electrical conductivity of aluminum alloys.During the four-pass equal channel pressing at 150°C,with the increase of pass times,the conductivity of the four alloys with 0Ca,Mg-8Al-18Ca,Mg-10Al-27Ca and Mg-30Ca added gradually increased,peaking after aging,54.38%IACS,52.33%IACS,53.27%IACS,and 54.53%IACS,respectively.The tensile strength of the four alloys increased significantly after post-ECAP aging,which were 291.6 MPa,336.4 MPa,337.1 MPa and 293.2 MPa,respectively.The alloy with Mg-10Al-27Ca added has the best overall performance.