The (1¯012) twin boundaries experimentally observed in hexagonal-close-packed metals are often serrated rather than fully coherent. These serrated coherent twin boundaries (SCTBs) consist of sequential (1¯012) coherent twin boundaries and parallel basal–prismatic planes serrations (BPPS). We demonstrated that the formation of BPPS is geometrically and energetically preferred in the SCTBs

and an SCTB thus migrates by glide and climb of twinning dislocations

combined with atomic shuffling. Particularly

the climb mechanism

combined with the density and the height of BPPSs in the SCTBs

could be crucial in controlling twinning and de-twinning

and twinning-associated hardening.