Abstract
The properties and microstructure evolution of quaternary Cu-Ni-Co-Si alloys with different Ni/Co mass ratios were investigated. The microstructure and morphological characteristics of the precipitates were analyzed by using electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The mechanical properties and conductivity of the alloys were significantly improved after the addition of Co. The grains presented an obvious growth trend with an increase in Ni/Co mass ratios, and the appropriate Co accelerated the recrystallization process. The δ-(Ni, Co)2Si phases of the Cu-Ni-Co-Si alloys and δ-Ni2Si phases of the Cu-Ni-Si alloys shared the same crystal structure and orientation relationships with the matrix, which had two variant forms: δ1 and δ2 phases. The precipitates preferential grew along with the direction of the lowest energy and eventually exhibited two different morphologies. Compared with that of the Cu-Ni-Si alloy, the volume fraction of precipitates in the alloys with Co was significantly improved, accompanied by an increase in the precipitated phase size. The addition of Co promoted the precipitation of the precipitated phase and further purified the matrix. A theoretical calculation was conducted for different strengthening mechanisms, and precipitation strengthening was the key reinforcement mechanism. Moreover, the kinetic equations of both alloys were obtained and coincided well with the experimental results.
Highlights
IntroductionRecent years have witnessed more miniaturized, multifunctional and intelligent contemporary electronic products, a larger scale of integrated circuits and the increasing microthinning of lead frame materials used in integrated circuits being produced [1]
Introduction published maps and institutional affilRecent years have witnessed more miniaturized, multifunctional and intelligent contemporary electronic products, a larger scale of integrated circuits and the increasing microthinning of lead frame materials used in integrated circuits being produced [1].it is of great significance to develop an elastic copper alloy with high conductivity and performance while developing electrical connectors
Ternary Cu-Ni-Si alloys exhibit a high strength of 600–900 MPa and electrical conductivity of 35–45% International Annealed Copper Standard (%IACS), but it means few spaces are left for developing ternary alloys [4,5]
Summary
Recent years have witnessed more miniaturized, multifunctional and intelligent contemporary electronic products, a larger scale of integrated circuits and the increasing microthinning of lead frame materials used in integrated circuits being produced [1]. It is of great significance to develop an elastic copper alloy with high conductivity and performance while developing electrical connectors. Cu-Ni-Si-based alloys are typical age-hardened alloys with an outstanding combination of strength and electrical conductivity and serve as a key raw material for large-scale integrated circuit lead frames. Ternary Cu-Ni-Si alloys exhibit a high strength of 600–900 MPa and electrical conductivity of 35–45% International Annealed Copper Standard (%IACS), but it means few spaces are left for developing ternary alloys [4,5].
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