• LPSO phase suppressed the AGC of welded Mg-RE alloys during heat treatment. • The grain boundary pinning mechanism within FZ was elucidated. • AGC effect on the precipitation behavior of the welded joint was revealed. • The joint shows superior strength-ductility synergy with a joint efficiency of ∼97%. Fusion zone (FZ) of Mg-RE alloy joints usually exhibits severe abnormal grain coarsening (AGC) during post-weld heat treatment (PWHT), deteriorating the comprehensive mechanical properties. To overcome this long-standing challenge, a microstructural stabilization strategy was applied by developing a novel filler wire to in-situ form thermally stable 14H-LPSO phases within FZ of a Mg-9Gd-3Y-0.5Zr alloy. These basal-oriented LPSO precipitates provide exceptional pinning at grain boundaries, suppressing AGC during PWHT without compromising strength. In addition, rapid solidification of fusion welding enables homogeneous LPSO distribution and thus eliminates the stress concentration in FZ. The resultant TIG-welded joint achieves a record ultimate tensile strength of 364.7 MPa with a joint efficiency of 97.2%, representing a 41% strength enhancement over conventional Mg-RE alloy joints. This work establishes a paradigm for stabilizing FZ through controlled phase engineering.
Li et al. (Sun,) studied this question.