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A new type of Al-Mg-Si-Cu aluminium alloy with high ductility was studied in the present work. The microstructure features and mechanical properties of this alloy were systematically characterized by scanning electron microscopy (SEM), electron back-scatter Diffraction (EBSD), high resolution transmission electron microscopy (HRTEM) and tensile and fatigue test. The percentage of sub-grain boundary under forging and aging process reaches up to 72% which can be attributed to the suppression of recrystallization by the nano-sized AlMnCrSi dispersoids. The combination of mechanical properties of the new alloy product in aged state showed that the ductility keeps in the range of 15~18%, yield strength and tensile strength are 310MPa and 380MPa respectively, fatigue strength ranges from 130MPa to 135MPa. It presents more excellent properties than commercial 6061 alloy for the nano-sized AlMnCrSi dispersoids, initial-β” precipitates and high percentage of sub-grain boundary.