The deformation mechanisms of Mg, Zr, and Ti single crystals with different orientations are systematically studied by using molecular dynamics simulations. The affecting factors for the plasticity of hexagonal close-packed (hcp) metals are investigated. The results show that the basal <a> dislocation, prismatic <a> dislocation, and pyramidal <c + a> dislocation are activated in Mg, Zr, and Ti single crystals. The prior slip system is determined by the combined effect of the Schmid factor and the critical resolved shear stresses (CRSS). Twinning plays a crucial role during plastic deformation since basal and prismatic slips are limited. The $\left\{10\overline{1}2\right\}$ twinning is popularly observed in Mg, Zr, and Ti due to its low CRSS. The $\left\{10\overline{1}1\right\}$ twin appears in Mg and Ti, but not in Zr because of the high CRSS. The stress-induced hcp-fcc phase transformation occurs in Ti, which is achieved by successive glide of Shockley partial dislocations on basal planes. More types of plastic deformation mechanisms (including the cross-slip, double twins, and hcp-fcc phase transformation) are activated in Ti than in Mg and Zr. Multiple deformation mechanisms coordinate with each other, resulting in the higher strength and good ductility of Ti. The simulation results agree well with the related experimental observation.

Pyramidal slip mechanism plays an important role in c-axis micro-compression of hexagonal closed-packed metals. In this article, the detailed slip paths, respectively, on and planes in magnesium single crystal are given by molecular dynamics. The pyramidal slip on plane is suggested to consist of an edge-type partial dislocation and opposite basal movements on neighbouring basal planes, while the slip dissociation is achieved by two partial dislocations with a strip of stacking fault. Results imply that the slip on plane is more likely to nucleate with a relatively easy dissociation type comparing to the one on plane. No twinning is found under c-axis compression by examining the stepwise movement of atoms involved, fully supporting the recent experimental observations of micro-compression and the theoretical analysis on twinning formation proposed by our previous work.