Effects of thermo-mechanical processing on microstructure and properties of Cu-0.9Hf alloy

Cu-Hf alloys, which exhibit electrical conductivity up to 80 %IACS, are promising high-strength and highconductivity copper alloys. However, the performance of Cu-Hf alloys under different thermos-mechanical processes (TMP) remains unclear. This work systematically investigates the microstructural evolution and property changes in Cu-0.9Hf alloy subjected to four prevalent TMP routes, including solid solution-aging, solid solution-cold rolling-aging, multi-step TMP, and TMP combined with pre-aging. The pre-aged Cu-0.9Hf alloy demonstrates the highest strength (666 MPa), while the multi-stage TMP Cu-0.9Hf alloy achieves optimal comprehensive properties: 628 MPa and 77.7 %IACS. The Corresponding strengthening-mechanism analysis indicates that dislocation-strengthening is the primary contributor. Additionally, the Cu-0.9Hf alloy exhibits good high-temperature softening resistance in this work. Microstructural analysis reveals that despite precipitate coarsening and morphological evolution during aging, the Cu matrix maintains a high dislocation density without apparent recrystallization, even at the over-aging stage. The pinning effects of Hf-containing second phases on dislocations during aging are crucial for the alloy's excellent softening resistance.