Optimizing mechanical properties of magnesium alloys by philosophy of thermo-kinetic synergy: Review and outlook

Although several strategies (including grain refinement, texture adjustment, precipitation hardening, etc.) have been verified to effectively improve the mechanical properties of lightweight magnesium (Mg) alloys, considerable efforts are still needed to be made to comprehensively understand the potential mechanisms controlling complex microstructures and deformation behaviors exhibited by the hexagonal close-packed host lattice of Mg, thus assisting the rational design of materials at a more physical level. As the cornerstone of this review, a universal rule, the so-called synergy of thermodynamics and kinetics (i.e., thermo-kinetic diversity, correlation and connectivity), including a recently proposed theory of generalized stability (GS), is introduced to deepen our understanding on common behaviors in Mg alloys (i.e., deformations (slip and twining modes), phase transformations (especially for precipitations) and interactions in between) at a new perspective. Guided by the GS theory, typical cases for Mg alloys design are qualitatively evaluated to reemphasize the traditional strengthening and toughening strategies mentioned above and to illuminate their exquisite coordination for breaking through the trade-off relationship between strength and ductility, corresponding to a typical thermo-kinetic pair (i.e., high driving force (∆G) - high GS). To produce the Mg alloys with superior strength-ductility balances, the potential capacity of this GS theory for guiding processing path design is discussed, finally.