Influence Of Composition And Processing On Microstructure And Properties Of Cu-Cr-Zr System Alloys

Aging-harden Cu-Cr-Zr system alloys possess high strength and excellent electrical conductivity,which have been widely used in the field of electric power,electronic and machinery manufacting industries,etc.They are also main materials of contact wires used in high-speed railway and lead frames used in integrated circuits.Studies show that the addition of Cr and Zr in Cu-Cr-Zr alloys could refine the Cr-rich and Zr-rich phases due to the interaction of Cr and Zr elements,which results in the enhancement of strength and electrical conductivity.In addition,the strength,plastic,conductivity and thermal stability can be improved by adding trace rare earth,which contributes that the matrix is cleaned,dendritics are eliminated and grains are refined.But there are also different opinions and conclusions on the impact of addition of Cr,Zr,rare earth,deformation and heat treatment process on the texture evolution,precipitations and properties of Cu-Cr-Zr system alloys.Thus,in this study,Cu-Cr-Zr-La alloys with different addition of Cr,Zr or La were prepared,followed by homogenization,rolling,solution,rolling again and aging treatment.The microstructures,mechanical and electrical properties were characterized by optical microscopy(OM),scanning electron microscope(SEM),transmission electron microscopy(TEM),tensile strength,hardness and conductivity test.The results show that:In as-cast Cu-Cr-Zr alloys,portion of Cr and Zr precipitated in Cr phases or Zr-rich phases,and other portion was dissolved in Cu matrix,which strengthened the alloys.Lots of Cr phases in bar or round shape were distributed in grain boundaries and interior of grains.Zr-rich phases in size of several micrometers were distributed in the interior of grains.Therefore,with the addition of Cr or Zr,the Cu-Cr-Zr alloys were strengthened,while the ductility and the electrical conductivity decreased due to the distortion of crystal lattice.Cu matrix was cleaned and grains were refined by adding trace La,which resulted in higher tensile strength,elongation and electrical conductivity.However,when adding more rare earth La,some coarse intermetallic compound CuxLa and rare earth oxides were produced mostly in grain boundaries,which would severely harm to the properties of Cu-Cr-Zr alloys.The Cu-0.45Cr-0.2Zr-0.13La alloy possessed a good combination of room temperature tensile strength,elongation and electrical conductivity.Additionally,aging behaviors of Cu-Cr-Zr-La alloys with different content of La were studied,before which the alloys were processed by homogenization,rolling,solution and rolling again.After homogenization,rolling and solution processes,Cu-Cr-Zr-La alloys reached the peak aging and the hardness improved by 113 HV when aged at 470? for 60 min.The phase transformation kinetics equation of the alloy aged at 470? can be expressed as f=1-exp)(-0.03493t~1.0462).After homogenization,rolling,solution and rolling again processes,Cu-Cr-Zr-La alloys reached the peak aging and the hardness improved by 66 HV when aged at 430? for 60 min.The phase transformation kinetics equation of the alloy aged at 430? can be expressed as f=1-exp(-0.03487t~1.0467),which indicated that peak aging temperature was lowered and aging process was accelerated by the energy stored among rolling process before aging treatment.The grains of Cu-Cr-Zr-(La)alloys,treated by homogenization,rolling,solution,rolling again and aged at 430? for 60 min,were in long bar shape,which indicated that the aging temperature was lower than recrystallization temperature.At the same time,dominated {001}<100>texture,with slight {112}<111>and {011}<100>texture,whereas dominated{011}<211>texture,with slight {011}<100>and {001}<100>texture,were determined in aged Cu-Cr-Zr and Cu-Cr-Zr-La alloys,respectively.The tensile strength,hardness and electrical conductivity of Cu-Cr-Zr-La alloys aged and before aged improved significantly with La addition,followed by a decline.After aging treatment,the Cu-0.45Cr-0.2Zr-0.13La alloy revealed optimal tensile strength,hardness and electrical conductivity.The tensile fracture model of the alloys aged at 470? for 60 min without rolling again was a mixed fracture of ductile dimple fracture and intergranular fracture,whereas the tensile fracture model of the alloy aged at 470? for 60 min with rolling again was dimple fracture.