Heat treatment, tensile and creep behaviors of Mg-Gd-Y-Zr alloy by novel near-liquidus squeeze cast

• Optimized T4 and T6 regimes were developed for NSC alloys to maximize strengthening. • NSC alloy exhibits improved strengths and comparable ductility to GC and SC alloys. • The creep behavior was systematically investigated among the three casting techniques. • Creep resistance decreased progressively from GC to SC and NSC with grain refinement. • β′ precipitates coarsened during creep and partially transformed into β' F phase. • PFZs formed along GBs during creep accompanied by secondary phase at the GBs. The microstructure evolution during solution heat treatment, age hardening responses, and tensile behaviors under varied heat treatment states of an Mg-Gd-Y-Zr alloy (VW93K) processed by novel near-liquidus squeeze casting (NSC) were studied. Moreover, the compressive creep behavior and microstructural evolution of T6-treated VW93K alloys prepared via gravity casting (GC), conventional squeeze casting (SC), and NSC were investigated comparatively. Creep tests at 200–250 °C under 50–120 MPa revealed that steady-state creep rates increased gradually from GC to SC and NSC alloys, although remaining within the same order of magnitude. The consistent combination of stress exponents ( n ≈ 2), grain size exponent ( p ≈ 2), and activation energies ( Q ≈ 73.4∼99.1 kJ/mol) across all processing routes unequivocally identifies grain boundary diffusion accommodated by grain boundary sliding (GBS) as the rate-controlling mechanism. TEM observations reveal significant microstructural degradation during creep, characterized by precipitate coarsening and the transformation of spindle-like β′ into elongated, chain-like structures. This evolution is driven by the formation of β′ F ''bridging'' connectors between β′ precipitates, which leads to a loss of coherency and pinning efficiency. Dynamic precipitate-free zone (PFZ) also observed, acting as softened pathways for localized strain accumulation and facilitating GBS. The results highlight a trade-off where the grain refinement inherent to NSC enhances room-temperature strength but compromises creep resistance due to accelerated grain-boundary mediated processes. Alloy design strategies, including stabilizing precipitates and introducing high-melting secondary phases at grain boundaries, are proposed to optimize both strength and creep resistance. These findings provide guidance for future design of creep resistant Mg-RE alloys and corresponded casting technologies.