The Precipitation Behavior of a Cu-Ni-Si Alloy with Cr Addition Prepared by Heating-Cooling Combined Mold (HCCM) Continuous Casting

Abstract

A Cu-Ni-Si alloy containing (Ni + Si) ≥ 5 wt.%, with the addition of Cr, is fabricated by HCCM continuous casting and two steps of aging treatment. The evolution of the microstructures and precipitations, as well as the effect of Cr atoms, is studied in this paper. An excellent combination of mechanical property (hardness HV 250–270) and electrical conductivity (46–47 %IACS) is obtained by the first step aging at 500 °C for 0.25 h and the second step aging at 450 °C for 1 h. The cold rolling and aging process are directly conducted on the solution treated specimens fabricated by HCCM continuous casting process without hot deformation, since the excellent homogeneity of matrix is obtained by solution treatment with δ-Ni2Si precipitates dissolved. It is found that the formation of discontinuous precipitation is suppressed by the formation of Cr3Si cores of 5–10 nm before the formation δ-Ni2Si. Then, the nucleation and growth of δ-Ni2Si precipitates occurs around the boundaries of these Cr3Si cores, leading to an enhanced nucleation rate. This study provides a promising direction for the design and optimization of Cu-Ni-Si alloys based on the further understanding of the effect of the addition of Cr.

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“…For Ni:Si > 2 electrical conductivity decreases because solute ratios (Ni:Si) are no more in perfect precipitate stoichiometry and extra Ni goes into the solid solution. Therefore, the peak at atomic ratio 2 signifies the precipitation of Ni 2 Si in the system, aligning with existing literature findings [85,86]. Similarly, Figs.…”

“…When the Cr:Si and Ni:Sn atomic ratio increases from 0 to 3, electrical conductivity continuously rises because of some precipitation of Cr-Si and Ni-Sn. But after 3, electrical conductivity stops increasing and therefore, this point of optima at 3 signifies the respective precipitation of Cr 3 Si and Ni 3 Sn in the system, which is in good agreement with the precipitate stoichiometry reported in the available literatures [85,87].…”