Ultrafine-grained structures were obtained in a solution-treated Al-Mg-Si (6060) alloy processed by high-pressure torsion at ambient temperature, 100 °C and 180 °C. Processing at 100 °C provided the highest hardness and the smallest average grain size because of the enhanced segregation of solutes at grain boundaries which hindered grain growth during the processing. This research demonstrated the importance of optimising processing temperature to enhance grain refinement in high-pressure torsion processing.