Achieving bimodal grain structure via cold rolling remains a challenge for Al–Mg alloys. In the present work, a high tensile strength (∼525 MPa) and ductile (∼14%) Al–9Mg alloy was fabricated by a novel hard-plate rolling (HPR) route with a single-pass thickness reduction of 75%. Increasing solute Mg content promotes a bimodal structure and a high dislocation density in the HPRed Al–Mg alloys due to the severely retarding effect of Mg solutes on dynamic recovery/recrystallization. The simultaneous high ductility and strength is due mainly to the strong work hardening ability deriving from the bimodal grain structure and the high solute Mg content.