Bulk ultrafine-grained metals (grain size 0.1~1μm) with unique physical and mechanical properties is one of most interesting topic in the field of materials research. Equal channel angular pressing (ECAP) is an effective route to obtaining bulk ultrafine-grained metals through severe plastic deformation (SPD). Deformation parameters of ECAP and die design are the key factors for ultrafine-grained metals. Although the outer arc angle of the ECAP die has important effects on materials flow, microstructure and...