The effects of high-pressure torsion (HPT) processing on an Al-Mg-Si alloy (AA6060) have been investigated comprehensively. We show that the processing temperature has complex effects on the strength, grain refinement and solute nanostructures of the alloy. Ten-revolution HPT processing at room temperature produced the highest yield strength of 475 MPa, which is similar to a high-strength Al alloy. However, processing at 100 degrees C produced the finest grains due to the strong solute segregation to grain boundaries and the formation of high-density precipitates that pin grain boundaries. Processing at 180 degrees C led to significant decomposition of the alloy and the formation of coarse precipitates. This research demonstrates that solute nanostructures provide key information for unravelling the origins of HPT-induced strengthening and grain refinement, and reveals the important opportunities for "engineering" solute nanostructures to enhance grain refinement in HPT processing. (C) 2013 Acta Materialia In