Cryogenic strength-ductility synergy in Mg-6Gd-1Zn alloys with bimodal grain structure coupled with basal lamellar phase

Achieving simultaneous strength and ductility at cryogenic temperature (CT) remains challenging for Mg alloys. An extruded Mg-6Gd-1Zn (wt.%) alloy with bimodal grain structure and basal lamellar phases exhibits anomalous strength-ductility synergy at CT. Mechanical incompatibility between soft DRXed and hard unDRXed regions generates geometrically necessary dislocations (GND) accumulation and dominant hetero-deformation-induced (HDI) hardening. Basal lamellar phases intensify elastic and plastic incompatibility, steepening GND gradients and back stress at CT. The coupled bimodal grain structure and basal lamellar phases elevate local resolved shear stress, activating non-basal slip even in grains with low Schmid factors (SF), enabling enhanced cryogenic strength-ductility synergy.