Abstract: The AlMgSi alloy is widely employed in automotive vehicles; however, challenges such as cracking often arise during the hemming process (180° bending). Based on the molecular dynamics simulations and experiments, this study investigated the effects of the Mg-Si(-Fe) clusters' size and number on the mechanical properties of 6xxx Al alloys. The results showed that medium-sized MgSi clusters (containing 10-19 atoms) at the grain boundaries (GBs) enhanced the strength of GBs, which can effectively inhibit crack initiation and significantly suppress the intergranular cracking. In addition, the ductility and brittleness of the model with the Fe-containing phase are greatly affected by the Si/Fe ratio (~0.71). Tensile experiments confirmed that the failure morphology exhibited a distinct brittle fracture when the Si/Fe of the phase is 0.90. The pre-aging treatment promoted the dispersion of the solute atoms, thereby reducing the yield strength of the AA6016 Al alloy to ~120 MPa, which was beneficial for improving its hemming performance. Furthermore, pre-aging facilitates the generation of finer Mg-Si phases at the GBs during bake hardening.