Simultaneous enhancement of strength and plasticity in extruded Mg-4Gd-0.5Zr alloys: Tailoring grain size and precipitated phases via Nd and Y addition

Overcoming the strength-plasticity trade-off by regulating grain size and precipitation behavior remains a central challenge in magnesium (Mg) alloy development. This study investigates the synergistic improvement of strength and ductility in Mg alloys by partially substituting Gd with Nd and Y to tailor precipitation behavior and grain structure. Using extruded VK61 as the base alloy, the addition of Nd (VEK421) transformed Mg₅ Gd precipitates into Mg₅ (Gd, Nd), preserving the original phase structure. Further alloying with both Nd and Y (VWEK4111) refined the precipitates to nanoscale Mg₂₄ (Gd, Y, Nd) ₅. Compared to VK61, precipitate sizes in VEK421 and VWEK4111 were reduced by 25.8 % and 51.4 % and precipitate area fractions were increased by 12.6 % and 24.6 %, while grain sizes decreased by 34.4 % and 56.3 %, respectively. The alloying elements also influenced slip behavior, with Nd and Y suppressing basal <a> slip and promoting non-basal slip activity, thereby improving deformation uniformity. Tensile tests showed that VEK421 achieved a yield strength (YS) of 184.9 MPa and elongation (EL) of 33.6 %, representing increases of 15.6 % and 40.6 % over VK61. VWEK4111 further improved YS to 220.6 MPa (up 37.8 %) and EL to 26.9 % (up 15.5 %). These enhancements are attributed to grain refinement and activation of pyramidal <c+a> slip. This work demonstrates an effective alloy design strategy for cost-efficient, high-performance Mg alloys via microstructure and precipitation engineering.