Effect of zinc-doping on tensile strength of Σ5 bcc Fe symmetric tilt grain boundary

•LMIE mechanism of galvanized steel on hot tensile process was investigated by FPCTT.•Zn doped at GB leaded to expansion of chemical bonds, thus weakening bond strength.•The Fe (2)–Fe (−2) bond which maintained the tensile strength of GB was identified by the d-state electron of atoms.•The reduction of the Fe (2)–Fe (−2) bond strength after zinc-doped was indicated by the accumulated charge.