Revealing the abnormal softening mechanisms of Zn-xCu (x=2, 3) wrought alloys by gradually increasing ECAP numbers

Abstract

In this study, equal channel angular pressing (ECAP) was employed as a technique to gradually increase the input of strains on Zn-xCu (x = 2, 3; wt%) alloys and investigate their work softening behavior. The microstructure and mechanical properties of Zn–Cu alloys with various processing strains were systematically characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffractometer (XRD), electron back scattered diffraction (EBSD), transmission electron microscopy (TEM) and tensile tests at room temperature. The results showed that besides η-Zn matrix refined via dynamic recrystallization (DRX), nano-sized precipitated CuZn5 particles were formed in ECAP alloy. Compared with the as-cast alloy, the ultimate tensile strength (UTS) of 1P alloy (after 1 pass of ECAP) was significantly improved to 207 MPa. However, the UTS declined with further increasing ECAP numbers. The 12P alloy (after 12 passes of ECAP) exhibited low UTS of 114 MPa but with an obviously increased elongation of 121% (from 56% of 1P), indicating that the alloy had a softening behavior with increased plastic strains. The main reason for the decline of strength was attributed to the texture weakening, the lower contribution of solid solution strengthening caused by the growth of precipitated CuZn5 phase. The higher ductility of 12P alloy was mainly ascribed from grain refinement, increased continuous DRX softening and the Zn/CuZn5 phase boundary sliding. This work provides a promising insight into the improvement of softening behavior for Zn–Cu based alloys.