Towards mechanical performance paradox and behind thermo-kinetic origins of aluminum alloys with additional solutes (X = Mg, Cu and Si) from atomistic simulations

Dislocation glide and/or deformation twinning, which can be uniformly described as the kinetic behaviors of atoms driven by thermodynamics, play important roles in dominating mechanical performance and strength-ductility paradox of metallic alloys. In this work, the physical origins behind the mechanical performance paradox are investigated in light of thermo-kinetic synergy upon materials processing. Combining the classical dislocation theories with common strengthening mechanisms, the quantitative connections among yield strength, plastic strain and dislocation density are bridged by the driving force and energy barrier of dislocation motion. The FCC-Al and Al alloys with Mg, Cu and Si solutes are studied as typical representatives by performing molecular dynamics (MD) simulations to analyze the tensile behaviors. It turns out that the thermo-kinetic synergy is responsible for the strength-ductility exclusive behaviors. The yield strength and flow stress are enhanced with Mg, Cu and Si solutes adding in FCC-Al, due to the increased interactions between dislocations and solute atoms. All the Mg, Cu and Si solutes can benefit the mechanical responses of Al alloys. Increasing Mg content enhances the driving force and yield stress of Al-Mg alloys, but reduces the energy barrier and plastic strain. The solute Si addition can further increase the driving force and yield stress, but decrease the energy barrier and plastic strain of Al-Mg-Si alloys. Our investigation provides an innovative viewpoint for understanding the mechanical performance paradox of metallic alloys, and offers insightful guidance for designing advanced Al alloys with good mechanical performance.