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

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 degrees C for different times. The dependence of grain size on annealing twin density of prior alpha matrix phase over a range from 1.0 to 10 mu m and its effect on mechanical properties were investigated. The results show the high-density annealing twins generation in alpha phase substantially enhances the strength-ductility combinations and work hardening of the HHRed NAB. The HHRed NAB annealing at 800 degrees 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 mu m), which is closely associated with the promotion effect of the ultrafine precipitates on the annealing twins generation in the fine-grained stage.