Abstract: Over-aging softening due to second-phase particle coarsening is a prevalent issue in age-hardenable copper alloys, limiting their performance optimization and high-temperature applications. We propose a dislocation-assisted heterogeneous co-precipitation strategy for high thermal stability in Cu-Cr-Hf alloys, leveraging the dislocation sensitivity of Hf phase nucleation as a key element of this approach. Through this, we explore their precipitation behavior and observe two novel co-precipitation modes. In solution-treated alloys, asynchronous co-precipitation occurs: Hf phases nucleate at transformation-induced interfacial dislocations (TIIDs) within Cr/Cu phase boundaries after initial Cr precipitation. In deformed alloys, synchronous co-precipitation is observed, where Hf and Cr phases nucleate simultaneously at deformation-induced dislocations. The resulting composite nanoparticles formed via co-precipitation exhibit reduced interfacial energy. This inhibits nano-precipitate coarsening, dislocation annihilation, and copper matrix recrystallization, ultimately suppressing the over-aging softening of the alloy. After being processed by a single-pass “solution-cold rolling-aging” process, Cu-Cr-Hf alloy shows tensile strength of 597 MPa and electrical conductivity of 72 % international annealed copper standard, while maintaining high hardness after prolonged aging even at 500 °C, demonstrating an excellent strength-conductivity balance and high thermal stability. We envisage that this innovative mechanism of enhancing nanoparticle thermal stability through multi-precipitate co-precipitation can provide a pathway based on conventional industrial operations for optimizing advanced high-strength, high-conductivity copper alloys and promote their high-temperature service.

Key words: Copper alloy, High strength and high conductivity, Plastic deformation, Heat treatment, Phase transformation, Heat resistance