Multiscale stabilization mechanisms of β″ precipitates in Al–Mg–Si alloys: Mg5Al2Si4 dominance through thermodynamic-mechanical-interfacial synergy

Investigating the intrinsic characteristics of Al-containing precipitates in age-hardenable aluminum alloys and exploring their synergistic interactions with dislocations, interfaces, and the aluminum matrix represents a cutting-edge strategy for designing lightweight, high-strength aluminum alloys. This study elucidates the stability competition mechanisms among β″ precipitates (Mg5Si6, Mg5Al2Si4, and Mg4Al3Si4) in Al–Mg–Si alloys through multiscale computational analyses. First-principles calculations reveal that Mg5Al2Si4 exhibits superior thermodynamic stability, as evidenced by its minimized formation enthalpy and negative cohesive energy, which govern spontaneous nucleation and coarsening resistance. Furthermore, Mg5Al2Si4 demonstrates optimal mechanical properties, including shear modulus, Young's modulus, and Pugh ratio, synergistically enabling enhanced dislocation pinning capability and balanced strength-ductility synergy. Notably, interfacial analysis indicates that Mg5Al2Si4 effectively suppresses interfacial decohesion by stabilizing semi-coherent interfaces through the lowest interfacial energy and highest adhesion work among the studied phases. In contrast, Mg5Si6 exhibits inferior stability, functioning merely as a transient metastable precursor during aging. These findings establish Mg5Al2Si4 as the dominant strengthening phase in peak-aged conditions. By constructing a multiscale correlation framework integrating thermodynamic, mechanical, and interfacial properties, this work provides a universal paradigm for the design of precipitation-strengthened aluminum alloys.