Influence Of Hot And/or Cold Working And Yb Content On Mechanical And Electrical Properties Of Al-0.2(Sc,Yb)-0.04Zr Alloys

The Al-0.2(Sc,Yb)-0.04 Zr alloys(wt.%,weight percentage,the same as following)were fabricated by melting appropriate amounts of 99.991% high pure Al,Al-1.85 Sc,Al-4.38 Zr and Al-1.85 Sc master alloys in air.All as-cast alloys were homogenized at 640? for 24 h and water quenched.Then the alloys were subjected to four kinds of hot and/or cold working,which are cold rolling(CR),peak aging+cold rolling(PA+CR),hot extrusion+cold rolling(HE+CR)and hot extrusion+peak aging +cold rolling(HE+PA+CR),respectively.After annealed at different aging temperatures for 1h,the Vichers hardness,tensile properties and conductivities of the pre-treated alloys were measured.Combined with the microstructure observation,the effects of cold and/or hot working and Yb content on the comprehensive properties of Al-0.2(Sc Yb)-0.04 Zr alloys were analyzed and discussed.The Al alloy conductor with lower Sc content was anticipated to be developed.The metallographic examination shows that the grain size of the as-cast alloys was between 300~500?m,and increased with the increase of Yb content.After cold-rolling,the elongated grain and fibrous structures were formed.From the hardness test,one can be found that the hardness of the homogenized Al-0.2(Sc,Yb)-0.04 Z alloys can be apparently increased by aging.The peak aging temperature changes with the Yb contents.The peak aging temperature was about 330? for 0.05,0.1 and 0.15% Yb alloys while it was 280? for 0.20% Yb alloys without Sc.This difference should be associated with the higher diffusion of Yb in ?-Al matrix.In addition,four kinds hot and/or cold working can all result in the decrease of the peak aging temperatures,which indicates that the precipitation of secondary Al3(Yb,Sc,Zr)phase can be accelerated with the help of the dislocations and internal stress result from cold and/or hot working.It is to be noted that the cold rolled alloys with a high Sc/Yb rate still have aging strengthening effect during the second aging although the alloys were already aging strengthened during the first aging before cold rolling.At the same treatment of cold and/or hot working,the hardness of Al-0.2(Sc,Yb)-0.04 Zr alloys decreased with the increase of Yb contents.Similar to the hardness results,the hot and/or cold working can further improve the mechanical properties of Al-0.2(Sc,Yb)-0.04 Zr alloys;furthermore,the strength of alloys decreased with the increasing Yb content.The best strength were obtained by HE+PA+CR+A treatment for all alloys containing Sc while that can be acquired by PA+CR+A treatment for alloys free of Sc.Considering the strength requirement(?159MPa)of international standard IEC 62004 on thermal-resistant aluminum alloy conductor,the Sc contents of Al-0.2(Sc,Yb)-0.04 Zr alloys should be above 0.1%.After the final peak aging,the tensile strength of CRed,PA+CRed,HE+CRed and HE+PA+CRed Al-0.1Sc-0.1Yb-0.04 Zr alloy were 171.07±5.51,173.56±5.27,164.59±2.40 ? 180.75±1.56 MPa,respectively while the elongation ? was all about 12%.Both tensile strength and elongation of Al-0.1Sc-0.1Yb-0.04 Zr alloy can satisfy the requirement of international standard IEC 62004 on heat-resistant aluminum alloy conductor.The room temperature electrical resistance tests showed that that the electrical conductivity can be increased by the formation of secondary Al3(Yb,Sc,Zr)precipitation during aging and the closure of as-cast micro-crack during hot-extrusion while it can be decreased by the increasing dislocations and internal stress resulted from cold rolling.With increasing Yb content,the electrical conductivity of four kinds of hot and/or cold worked Al-0.2(Sc,Yb)-0.04 Zr alloys increased approximately while it decreased firstly and then increased after peak ageing;furthermore,the 0.10% Yb alloy had the lowest electrical conductivity.After peak aging,the relative electrical conductivity at 20oC(?20)of the CRed,PA+CRed,HE+CRed,and HE+PA+CRed Al-0.1Sc-0.1Yb-0.04 Zr alloy were 58.20±0.36,58.95±0.35,60.26±0.38,and 59.81±0.28%IACS,respectively,which can basically satisfy the highest requirement of relative electrical conductivity(60%IACS)of international standard IEC62004 on heat-resistant aluminum alloy conductor.In summary,Al-0.1Sc-0.1Yb-0.04 Zr alloy has better both mechanical and electrical properties,as well as a low cost.After the final peak aging,the tensile strength,yield strength,elongation,and relative electrical conductivity at 20 oC of HE+PA+CRed Al-0.1Sc-0.1Yb-0.04 Zr alloy were 180.75±1.56 MPa,166.42±2.19 MPa 12.12±0.83%,and 59.81±0.28%IACS5,respectively.The comprehensive properties of this alloy can satisfy the requirement of AT1,AT3,and AT4 alloys specified by international standard IEC 62004.