Effect of microstructure on the mechanical properties of ultrafine-grained Cu-Al-Ni alloys processed by deformation and annealing

In this research, ultrafine-grained Cu-7at%Al-3at%Ni alloys with a twin structure and precipitates were prepared by cold rolling+aging+cold rolling+aging (CR+ACA) and multi-directional forging+aging+cold rolling+aging (MDF+ACA). In contrast with un-deformation sample, significant increases in strength were obtained by MDF+ACA and CR+ACA, reaching 803.7 MPa and 722.8 MPa respectively, while maintaining a good elongation of 9.5 % and 8.4 %. Compared with CR+ACA, this is noted that a synergistic improvment in strength and elongation is achieved after MDF+ACA. The effect of microstructure on strength and elongation was investigated and the contribution of each strengthening mechanism for strength was analysed. The results show that the enhancement in strength is due to the increased dislocation density as well as decreasing grain size formed in the MDF+ACA process. The higher twinning fraction in the sample after MDF+ACA leads to an increase in elongation due to the ability of twins to storage dislocations which can increase the strain hardening capability of the alloy. In addition, the current work describes a refinement mechanism for obtaining ultra-fine grains using these two different deformation processes by phase-field crystal (PFC) method simulation. The results of this study will help in further preparation of copper alloys with synergistic improvement strength and elongation.