Enhancing strength-ductility of the aluminum bronze alloy by generating high-density ultrafine annealing twins

Highlights: • Nickel aluminum bronze alloys with ultimate strength of 1148.3MPa, yield strength of 843.2MPa and elongation of 15.2% were prepared. • High-density ultrafine twins was achieved by heavy warm rolling and subsequent short-time heat treatment. • The strengthening effect of the twin boundaries were both directly observed and theoretically discussed. • Classical Pande model was discussed and the promotion effect on the generation of annealing twins by ultrafine precipitates in the fine-grained stage was pointed out. In this work, nickel aluminum bronze (NAB) alloys with high-density nano/ultrafine annealing twins were fabricated by heavy hot rolling (HHR) and the subsequent annealing treatment at 800 °C for different times. The dependence of grain size on annealing twin density of prior α matrix phase over a range from 1.0 to 10 μm and its effect on mechanical properties were investigated. The results show the high-density annealing twins generation in α phase substantially enhances the strength-ductility combinations and work hardening of the HHRed NAB. The HHRed NAB annealing at 800 °C for 2 min, with the highest twin boundary density, exhibits and excellent comprehensive mechanical properties with a yield strength of 843.2 MPa, ultimate strength of 1148.3 MPa, and uniform elongation of 15.2%. The analysis shows that the formation of these high-density ultrafine twins is mainly attributed to the large amount of deformation energy storage, high-density defects, and ultrafine precipitates of the dispersion distribution induced by HHR. It was found that the dependence of the twin density with grain size has some deviations from the classical Pande's model in the fine-grained stage (1– 2 μm), which is closely associated with the promotion effect of the ultrafine precipitates on the annealing twins generation in the fine-grained stage.