Study on the microstructure and mechanism of stress relaxation behavior of Cu–Ni–Si alloy by two-stage rolling deformation.

In this paper, the effect of the second-stage rolling deformation of Cu–Ni–Si alloy on its stress relaxation resistance was studied, and the mechanism of the change in microstructure and properties before and after stress relaxation was explored. The results show that the tensile strength and yield strength of Two-stage rolling peak aging (TRPA) 43.7 %, TRPA68.8 %, TRPA80.3 % and TRPA96.1 % alloys at 150 °C are close. After stress relaxation, the stress relaxation rates of these alloys are 7.7 %, 11.24 %, 14.69 % and 19.4 %, respectively. It is found that the smaller the second-stage rolling deformation, the better the stress relaxation resistance of the alloy, especially the stress relaxation resistance of the TRPA43.7 % alloy, which is 60.31 % higher than that of the TRPA96.1 % alloy. According to EBSD analysis, it was found that the increase in the number of twins can improve the stress relaxation resistance of the alloy. However, the occurrence of recrystallization reduces the stress relaxation resistance. Additionally, it was determined that the precipitated phase is the δ-Ni 2 Si phase with an orthogonal structure. Before stress relaxation, the size of the precipitated phase of the alloy with TRPA96.1 % is larger than that of the alloy with TRPA43.7 %, and after stress relaxation, the precipitated phase further grows. The influence of the interface relationship between δ-Ni 2 Si phase and Cu matrix on the stress relaxation properties of TRPA43.7 % and TRPA96.1 % alloys before and after stress relaxation was investigated using the mismatch theory. In summary, this study reveals that the size of δ-Ni 2 Si phase, dislocation density and recrystallization are the key factors affecting the stress relaxation resistance of Cu–Ni–Si alloy. • In the two-stage rolling aging process, by applying a smaller deformation in the second-stage rolling and then undergoing a second-stage peak aging, the stress relaxation resistance of the alloy is improved by 60.31 % while ensuring that the hardness, strength, and electrical conductivity of the alloy undergo minimal changes. • The influence of the second-stage rolling deformation on the stress relaxation resistance of Cu–Ni–Si alloy was analyzed. Through the two-stage rolling aging process, δ-Ni 2 Si phases with sizes in the range of 5–10 nm and an orthogonal structure were obtained. Additionally, the formation of twinning effectively pinned mobile dislocations, thereby enhancing the stress relaxation resistance of the alloy. • The mechanism for enhancing stress relaxation resistance was elucidated through analysis of the morphology, size, phase interface relationships, dislocation density, twinning, recrystallization, and other factors of the second phase. • A stress relaxation dynamic regression equation was established. This equation not only predicts the residual stress and stress relaxation rate within a specific time frame but also provides a rough assessment of the alloy's stress relaxation resistance. [ABSTRACT FROM AUTHOR]