| The rapid development of electrical connectors to miniaturization and high performance with the advancement of technology requires the use of connector materials with high strength,high conductivity,resistance to high temperature softening,stress relaxation,and other comprehensive performance.The strength and electrical conductivity of conventional Cu-Ni-Si alloys can be improved with multi-stage aging treatment by obtaining a smaller,more diffuse continuous precipitate（CP）Ni2Si phase,however,it is challenging to maintain 1000 MPa and 45%IACS above at the same time.The Cu-Ni-Si alloy can be reinforced using discontinuous precipitate（DP）,a new strengthening method that has a lot of potentials to address the demand for high-performance connector materials while simultaneously improving strength and electrical conductivity.The study of Cu-Ni-Si alloy composition changes,as well as the size,morphology,and distribution characteristics of discontinuous precipitate,is important for understanding the effect of discontinuous precipitation on alloy properties.In this study,the high alloy content Cu-Ni-Si alloy is used to systematically investigate the impact and mechanism of Ni and Si atomic content and inclusion on the structure and properties of the alloy.Additionally,the precipitation behavior of discontinuous precipitate in the alloy with various compositions is investigated.By inserting various types of deformation bands into the pre-deformation,the precipitation behavior of Cu-Ni-Si alloy with discontinuous precipitate was explored,and the inherent relationship between the microstructure of the pre-deformation bands and the alloy parameters was investigated.The anti-softening behavior of various types of precipitate relative to the alloy was investigated,and the alloy’s softening mechanism was discussed.The strengthening mechanism for the strength and electrical conductivity of the Cu-Ni-Si alloy with discontinuous precipitate was investigated.The following were the main findings:（1）With an increase in Ni and Si content,the hardness of Cu-Ni-Si alloy tends to gradually increase,and the amount of aging time needed to reach peak aging steadily reduces.As the Ni and Si concentration of the alloy rises,the conductivity gradually decreases,proving that excessive Ni and Si content lowers the conductivity of the alloy.（2）When compared to the main properties of advanced copper alloys for connectors,Cu-4.75Ni-1.13Si alloy has higher electrical conductivity（50%IACS）and excellent strength（966 MPa）,while Cu-6Ni-1.42Si alloy shows higher strength（1071 MPa）and better electrical conductivity（46%IACS）.The excellent properties obtained in this system provide data guidance,as well as a theoretical foundation for the design and development of a discontinuous precipitate,strengthened Cu-Ni-Si system alloy.（3）The discontinuous precipitate’s growth model in Cu-Ni-Si alloy has been revealed,i.e.,the two ends of the discontinuous precipitate grow with the migration of grain boundaries and the advancement of the reaction front,respectively,and the discontinuous precipitate consumes the solid solution atoms at the front end of the interface and the continuous precipitate during the growth process.It replenishes Ni and Si atoms into the discontinuous precipitate via interfacial diffusion,causing it to grow along the length direction.（4）The peak aging time and peak hardness of the Cu-Ni-Si alloy are both accelerated by pre-deformation.The precipitation rate of the Cu-4.75Ni-1.13Si alloy increases with predeformation degree（0-2εu）,whereas the Cu-6Ni-1.42Si alloy has a faster precipitation rate for the 0.95εu pre-deformed alloy with slip band than the 2εu pre-deformed alloy with shear band.The 0.95εu pre-deformed alloy with slip band has a higher discontinuous precipitation rate than the 2εu pre-deformed alloy with shear band in the Cu-6Ni-1.42Si alloy.Because the slip band in the Cu-6Ni-1.42Si alloy provides a substrate for nucleation and a fast channel for atom diffusion,it speeds up the formation of discontinuous precipitation,whereas the shear band increases the number of substrate nucleation but hinders growth,which speeds up the nucleation of DP during the nucleation stage but severely slows down DP growth during the growth stage and ultimately slows down DP formation.（5）After 75%cold deformation and 30 minutes of annealing at 400℃,the alloy containing continuous precipitate reached a softening temperature of 505℃.After 85%and 98%cold deformation and 10 minutes of annealing at 400℃,the alloys containing discontinuous precipitate achieved softening temperatures of 575℃ and 515℃,respectively.Due to discontinuous precipitation’s stronger resistance to dislocation and grain boundary motion compared to continuous precipitation,discontinuous precipitation alloys display superior soften resistance.（6）Precipitation strengthening,solution strengthening,grain boundary strengthening,and work hardening are the primary mechanisms determining the aging state strength in alloys with continuous precipitate,with precipitation strengthening making a particularly clear contribution.Interfacial hindrance and work hardening are the key strengthening mechanisms in alloys having discontinuous precipitate that affect the strength of the aged state and deformed state.Of these,the interfacial hindrance mechanism has the most visible strengthening effect. |
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