Effect of the evolution behavior of precipitated phases during high-temperature aging on the microstructure and properties of Cu-Al-Sc alloy

The microstructure instability and property degradation of copper alloys under high-temperature service conditions are the key bottlenecks restricting their high-end applications. This paper systematically investigates the influence of the evolution of precipitated phases during high-temperature aging on the microstructure and properties of Cu-Al-Sc alloys. The results show that after high-temperature aging at 850 °C for 50 min, the Cu-Al-Sc alloy exhibits the best comprehensive performance: electrical conductivity of 97.6% IACS, microhardness of 111.9 HV, and tensile strength of 312 MPa. The excellent properties at the peak aging state are attributed to multiple synergistic mechanisms: the intragranularly dispersed metastable γ-Al₂O₃ precipitates (about 4.42 nm) maintain a coherent relationship with the matrix (misfit of 1.12%), contributing significantly to strengthening through Orowan strengthening, while the precipitation process greatly reduces the solute concentration in the matrix, achieving deep purification and ensuring high electrical conductivity. In addition, Sc segregation at grain boundaries and metastable ScAlO₃ precipitates effectively suppress grain boundary migration and abnormal grain growth through solute drag and Zener pinning effects. When the aging time is extended to 120 min, the precipitates coarsen to 9.06 nm, the number density decreases, and the interface relationship between the precipitates and the matrix changes from coherent to semi-coherent (misfit increases to 13.4%), resulting in weakened Orowan strengthening and a decline in mechanical properties. This study provides an important theoretical basis for actively controlling the evolution path of precipitated phases through process optimization to achieve a synergistic improvement in the electrical conductivity, strength, and thermal stability of the alloy.