Mechanical behaviors of metallic alloys dominated by thermo-kinetic synergistic effects upon materials processing

For most metallic alloys, improving strength is usually accompanied by losing ductility (and via versa) even if the work hardening rate keeps unchanged, however, the behind reasons still remain elusive to date. In the present work, we explore the underlying physics for such mechanical performance paradox from the perspective of synergistic effects between thermodynamics and kinetics of phase transition and deformation involved in materials processing. With age-hardenable aluminum alloys as typical examples, the hardening and softening effects are analyzed in terms of system energy accumulation and dissipation during precipitation nucleation and growth along with dislocation multiplication and annihilation. The key thermo-kinetic parameters of driving force and energy barrier are determined by performing relevant atomistic calculations. Analytical models for bridging mechanical performances and thermo-kinetics in terms of microstructural characteristics, which derive from classical phase transition and deformation theories, endow connotation for directing precipitation design, as confirmed by a 6xxx series alloy at the pre-determined aging temperature with ideal strength and ductility. Our work offers an insightful perspective toward understanding the strength and ductility paradox, which can benefit to further establish quantitative connections among processing routes, microstructures and mechanical performances of metallic alloys.