Strain rate and anisotropic effects on incipient plastic deformation of Zn–Cu–Ti alloy sheets

Abstract

Zinc alloys shows strong strain rate dependent and anisotropic mechanical behaviours, the mechanistic origin of which is however not fully understood. In this work, a combination of the experiments and crystal plasticity finite element simulations were used to gain an insight into the relation between deformation mechanisms, tensile deformation behaviour and texture evolution, especially for the incipient plastic deformation stage. To this end, specimens were cut from Zn–Cu–Ti alloy sheets at various orientations with respect to the rolling direction, and uniaxial tensile tests were conducted at different strain rates ranging from 10−3 to 5 × 10−2 s−1. The microstructure evolution with the deformation was examined by the electron backscatter diffraction technique. Crystal plasticity model was calibrated considering the effect of strain rate on the flow stress, and finite element simulations were carried out based on a representative volume element of the polycrystal zinc alloy. It is found out that the flow stress increases significantly, as the loading direction approaches the transverse direction, which results in a lower relative activity of basal slip and higher relative activity of non-basal ones. This, in turn, reduces the rotation of the c-axis of the crystallites towards ND during tensile tests. On the other hand, a positive strain rate sensitivity is found in the zinc alloy. Meanwhile, increasing strain rate leads to an obvious decrease in the activity of the pyramidal π-II slip systems, accompanied by more activated twinning systems. The lower activity of the pyramidal π-II slip at a higher strain rate probably hinders the development of CDRX and grain fragmentation at large strain levels.