Continuous cooling precipitation diagrams of Al-Mg-Si alloys

► Upper and lower critical cooling rates were determined for 5 Al-Mg-Si alloys. ► Hardness values after ageing are inversely proportional to specific precipitation heat. ► High temperature precipitation: Mg2Si (nucleating at primary precipitates); low temperature precipitation: β′ and B′. ► Maximum hardness achieved after ageing as long as quenching faster than critical cooling rate. ► Results of DSC, structural analysis and hardness testing are in high accordance.