Precipitation Of High Strength And High Electrical Conductivity Cu-Cr-Zr Alloy

Cu-Cr-Zr alloys have been widely used in high-speed electrical railway,heat exchange materials,integrated circuit lead frames and other industries for its properties with high strength and high electrical conductivity.Plenty of studies have focused on the effect of alloy compositions,the influence of processing technique and precipitation on properties and the strength mechanisms of the alloy.In this study,alloy ingots Cu-0.55wt%Cr-0.05wt%Zr were cast in a vacuum induction furnace.The as-cast ingots were subjected to solid solution,cold rolling and aging at different temperatures.The microstructures,mechanical and electrical properties were characterized by optical microscopy(OM),transmission electron microscopy(TEM),tensile test,hardness and conductivity test.In-situ TEM experiments were performed to investigate the dynamic interaction process between the Cr precipitates and dislocations.The aging processes were described by the phase transformation kinetics Avrami empirical equation basing on the conductivity variation.The results show that:Microstructural evolution of Cr precipitates formed during aging was investigated,its morphology transferred from typical coffee-bean contrast to rod-shaped with increasing aging temperature,and its structure transferred from FCC to BCC.The average size of precipitates ranged from?1.9 nm(aging at 500 ?for 1 h)to?150.7 nm(aging at 800 °C for 1 h).The relationship between Cr precipitates and the matrix transferred as coherent?semi-coherent?non coherent.The shearing mechanism was the prevalent one for the alloy aging at 500 and 600 ?.And the findings include:1)the contrast of the precipitation changed owing that the compensatory effect of the Cr precipitate and dislocation strain fields;2)the critical breaking angle for series dislocation cutting one precipitate decreased,thus the corresponding critical stress for the dislocation shearing the Cr precipitates increased;3)the movement of the dislocations through the Cr precipitates was quite jerky on a mesoscopic scale.The detachment of dislocation was recorded in the sample that aging at 700 °C.And when the aging temperature reached 800 °C,dislocations piled up cause of the large precipitates.However,the motion of dislocation was unobstructed in the sample after solid solution.The isothermal aging kinetics equation based on the phase transformation kinetics of conductivity variation:phase transformation kinetics equation aged at 400 °C:f = 1-exp(-0.00138t1.52677);phase transformation kinetics equation aged at 450 ?:f = 1-exp(-0.01972t1.01106);phase transformation kinetics equation aged at 500 ?:f = 1-exp(-0.01768t1.35668);phase transformation kinetics equation aged at 550 ?:f = 1-exp(-0.00122t1.79804)?Time-temperature-transformation(TTT)curves were established according to the equations.The isothermal aging phase transformation kinetic equation and the conductivity equation based on the conductivity variation were deduced.And the conductivity equation of alloy could be described as ? = ?0 + k[1-exp(-btn)],the phase transformation kinetic equation could be described as f = 1-exp(-btn).The value of k at 400?450?500?550 ? were 48.4?55.6?59.5 and 56.5;the value of b at 400?450?500?550 ? were 0.00138?0.01972?0.01768 and 0.00122;the value of n at 400?450?500?550 ? were 1.52677?1.01106?1.35668 and 1.79804;and the value of ?0 was 27.2.Time-temperature-transformation(TTT)curves were established according to the equations.