Morphological evolution of α-Mg and LPSO phases in MgY Cu1Ni1 alloys via thermal and electrical processing

This study investigates the microstructural evolution and phase transformation of extruded MgY x Cu 1 Ni 1 ( x = 1, 2, 3 at.%) alloys containing long-period stacking-ordered (LPSO) phases, subjected to either furnace heat treatment (FHT) or electropulsing treatment (EPT). In the as-extruded state, increasing Y content promoted LPSO phase transformation, grain refinement, and texture weakening through particle-stimulated nucleation. FHT at 773 K induced complete static recrystallization (SRX) and a distinct morphological transformation of the LPSO phase in two aspects: (i) lamellar to net-shaped distribution and (ii) blocky to rod-like structure. This transformation was strongly dependent on the Ni/Y ratio; the 1Y alloy exhibited the most pronounced change due to its low thermal stability and high endothermic enthalpy, whereas the 3Y alloy remained relatively stable. In contrast to FHT, EPT exerted a marginal effect on microstructural evolution, maintaining the elongated bulky morphology of the as-extruded state. This is attributed to the insufficient total thermal energy supplied during the rapid EPT cycles, which failed to trigger the endothermic dissolution of the thermally stable LPSO phase. These results indicate that thermal enthalpy dominates the phase transformation of LPSO Mg alloys, overshadowing potential athermal contributions of EPT.