Synergistic enhancement of strength and ductility in Mg-Gd-Y-Zn-Zr alloys through LPSO phases with multiple morphologies

As a crucial strengthening phase in rare-earth magnesium alloys, the content and morphology of the long period stacking ordered (LPSO) phase significantly influence the mechanical properties of the alloys, yet the specific regulatory mechanisms and synergistic effects remain unclear. In this study, Mg–Gd–Y–Zn–Zr alloy sheets with different LPSO phase contents and morphologies were fabricated by adjusting alloy composition and employing a multi-pass rolling process. The microstructure, mechanical properties, and strain distribution of the alloys were systematically analyzed using SEM, EBSD, and DIC techniques. The results demonstrate that a multi-morphology LPSO structure—comprising bulk (B-LPSO), intragranular lamellar (I-LPSO), and dispersed lamellar (L-LPSO) phases—was controllably achieved via a rolling-induced “W→LPSO” phase transformation. When the LPSO volume fraction reached 13%, all three morphologies coexisted in the alloy, which exhibited optimal tensile properties: ultimate tensile strength of 334 ± 14 MPa, tensile yield strength of 310 ± 5 MPa, and elongation of 13.8 ± 1.2%. These properties are markedly superior to those of the alloy containing only a single LPSO morphology with a higher content (18% LPSO). Mechanistic studies revealed that B-LPSO originates from the deformation-induced transformation of grain-boundary W-phase, I-LPSO forms through segregation at stacking faults within the supersaturated matrix, and L-LPSO results from the fragmentation, dissolution, and subsequent reprecipitation of I-LPSO. During deformation, B-LPSO and I-LPSO act as stress-bearing “hard zone” while the Mg matrix containing L-LPSO serves as a strain-accommodating “soft zone”. Their synergistic interaction leads to the simultaneous enhancement of both strength and ductility. Furthermore, the multi-morphology LPSO phases improve deformability and fracture toughness by promoting non-basal slip and inducing crack deflection. This study introduces a novel approach for regulating LPSO phase morphology through W–LPSO phase transformation, offering valuable insights for designing high-performance rare-earth magnesium alloys. • Reveal a novel dynamic W→LPSO phase transformation pathway during rolling • Achieve coordinated control of multiple LPSO morphologies • Obtain an optimized bimodal grain structure • Attain enhanced mechanical properties