The lightweighting of automobiles has imposed greater requirements on the mechanical properties of 6xxx series aluminium alloys. Thus, the development of 6xxx series aluminium alloy sheets for automotive bodies with high strength and toughness is urgently needed. The effects of adding 0.4 wt.% Sc on the microstructure and mechanical properties of Al-Mg-Si-Cu alloys were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and universal mechanical testing machines. The results show that the addition of 0.4 wt.% Sc significantly refines the as-cast microstructure of the alloy, transforming coarse columnar grains into fine equiaxed grains and resulting in a more uniform microstructure. Under the influence of Sc, the morphology of the brittle β-AlFeSi phase in the as-cast alloy changes, with coarse lamellar β-AlFeSi transforming into fine needle-like structures. In the solution-treated and aged rolled alloy with 0.4 wt.% added Sc, the main precipitates include the secondary Al3Scphase, the Q′ phase, and the β″ phase. The synergistic effect of these three phases enhances the alloy's strength. The addition of 0.4 wt.% Sc significantly improves the overall mechanical properties of both the as-cast and solution-treated + aged rolled alloys. For the as-cast Al-Mg-Si-Cu alloy, the average tensile strength, yield strength, and elongation increase from 151, 114 MPa, and 1.96% to 187, 127 MPa, and 3.44%, respectively. For the rolled Al-Mg-Si Cu alloy after solution treatment and aging, the average tensile strength, yield strength, and elongation improved from 368, 303 MPa, and 15.4% to 390, 330 MPa, and 20.8%, respectively.