Optimization of microstructure and properties of directionally solidified Cu−15Ni−8Sn alloy by multi-stage thermomechanical treatment

Abstract

The Cu−15Ni−8Sn alloy wire with a nano-layered structure was fabricated using directional solidification techniques and a multi-stage thermomechanical treatment. A systematic investigation was conducted on microstructure evolution and its impact on mechanical properties. After aging at 400 °C for 0.25 h, the ultimate tensile strength of the alloy reaches 1509 MPa, >200 MPa higher than that of the alloy after single thermomechanical treatment. Furthermore, grain refinement and heightened 〈111〉 fiber texture are identified as key factors contributing to the enhancement of the mechanical properties of the alloy. These findings highlight the importance of multi-stage thermomechanical treatment on microstructure evolution and mechanical properties of Cu−15Ni−8Sn alloy.

1. Introduction

Rapid advancements in aerospace and new energy vehicles have driven demand for high-performance electronic and electrical equipment, including electrical connectors [1,2]. Beryllium−copper alloy dominates the electronic connector market due to its advantageous properties including high strength, elasticity, and excellent wear resistance. However, the production of beryllium−copper alloy generates toxic dust, posing the substantial threat to human health [3,4]. Furthermore, it exhibits poor resistance to thermal stress relaxation and conductivity stability at high temperature.

The Cu−15Ni−8Sn alloy is renowned for its high strength and elasticity, and its strength and wear resistance are comparable to those of beryllium−copper alloy. Furthermore, it demonstrates outstanding stress relaxation resistance and stable conductivity under high-temperature conditions, making it considered the most promising alternative material to beryllium−copper alloy [5−8]. However, there is limited research on Cu−15Ni−8Sn alloy wires, because the Cu−15Ni−8Sn alloys prepared by traditional casting methods exhibit severe compositional segregation, making them prone to fracture during subsequent drawing [9,10]. This limitation hinders understanding of microstructure evolution and its impact on mechanical properties during the drawing and subsequent heat treatment processes of Cu−15Ni−8Sn alloys.

Furthermore, as a precipitation-hardened copper alloy, the pre-cold deformation treatment is crucial for Cu−15Ni−8Sn alloy, which can achieve a dual strengthening effect of work hardening and precipitation strengthening [11]. However, cold deformation can facilitate the formation of harmful γ-D03 phases, severely damaging the mechanical properties of the alloy [12]. Microalloying is an effective method to suppress the formation of γ-D03 phase. Studies have shown that adding elements such as Nb [13], Ti [14], Er [15], P [16], Co [17], Y [18], Fe [19], and Si [20] can delay γ-D03 phase formation. However, certain microalloying elements raise manufacturing costs and complicate component separation during the alloy recovery. Therefore, optimizing the deformation heat treatment process to balance the detrimental effects of γ-D03 phase formation on performance through optimization of the deformation heat treatment process is currently a research focus. Compared to the single-stage deformation heat treatment, multi-stage deformation heat treatment can achieve more precise microstructure control, thereby further improving material properties.