Traditional aluminium alloys, owing to their reliance on heat treatment processes, generally suffer from high energy consumption and significant deformation, which has driven the rapid development of non-heat treatment aluminium alloys. The composition of the Al-7Si-Mg-Cu-Mn alloy was optimized on the basis of JMatPro thermodynamic calculations, and the thermodynamic mechanism of the rare earth Ce in regulating the microstructure was revealed, providing theoretical support for the development of new non-heat treatment aluminium alloys. Through CALPHAD phase diagram calculations, it is found that controlling the Mg/Cu mass ratio to 1.53 can promote the formation of the Q phase (Al5 Cu2 Mg8 Si6 ) as the dominant strengthening phase, replacing the Mg2 Si and Al2 Cu phases, thereby achieving a synergistic improvement in strength and ductility. The addition of rare earth Ce to the optimized base alloy further enhances its performance. The mechanism of Ce microalloying is elucidated through experimental analysis and partial molar Gibbs free energy calculations: During solidification, Ce reduces the nucleation barrier of α-Al and inhibits dendritic growth, leading to a 34.2% reduction in secondary dendrite arm spacing; during the eutectic reaction stage, Ce selectively adsorbs on the silicon phase surface, transforming the eutectic silicon morphology from flake-like to fibrous. This synergistic optimization effect peaks at a Ce content of 0.3 wt.%. At this level, the alloy exhibits a tensile strength of 179 MPa and an elongation of  7.4%, representing increases of 17% and 51%, respectively, compared with those of the alloy without Ce. However, when the Ce content exceeded 0.3 wt.%, the coarsening of the Al-Si-Ce rare earth phases results in a decrease in the mechanical properties.