Exceptional fracture toughness in a high-strength Mg alloy with the synergetic effects of bimodal structure, LPSO, and nanoprecipitates

Abstract

Addressing the strength-toughness trade-off issue has been highly desirable for high strength Mg alloys. Herein, an Mg-9Gd-4Y-1Zn-0.5Zr (wt %) alloy is designed, and a yield strength of 430 MPa and plane-strain fracture toughness KIc of 23.1 MPa·m1/2 are achieved. Intrinsically, significant stress dissipation is induced by interactions between the tensile twinning and the kinking of the lamellar γ' phase, leading to increased KIc. Owing to the residual stress release, the fracture resistance is remarkably improved by the non-basal 〈a〉 and 〈c + a〉 dislocations activated in the fine dynamic recrystallized (DRXed) grains. Extrinsically, the microcracks initiated along the interfaces between lamellar γ' phase and α-Mg matrix facilitate the reduction of local crack-driving forces, resulting in an enhanced KIc. Moreover, the underlying toughening mechanisms were revealed, including the crack propagation path deflection caused by coarse deformed grains and microcrack shielding by the long-period stacking ordered (LPSO) and lamellar γ' phases.