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, Mg₅Al₂S_i4, 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.