In situ EBSD characterization of static recrystallization in a Mg-Zn-Ca (ZX30) alloy

The recrystallization behavior of a hot-compressed Mg–3Zn–0.1Ca (ZX30) alloy during static recrystallization was investigated in situ using electron backscatter diffraction (EBSD). The material was subjected to 5% plane-strain compression at 200 °C, and subsequently exposed to successive annealing treatments at 300 °C using a heating stage integrated with a scanning electron microscope (SEM)–EBSD system. The microstructural evolution and recrystallization process were monitored by performing EBSD scans immediately after each annealing step. Within this framework, three questions were addressed: (i) whether recrystallized grains can be reliably identified and quantified using EBSD metrics, (ii) whether recrystallized grains nucleate preferentially at grain boundaries, twin boundaries, or triple junctions, and (iii) whether grains with a Grain Orientation Spread (GOS) below 1° accurately represent the recrystallized fraction. Recrystallized grains were identified using grain-neighborhood, centroid, and orientation information through a graph-based approach. At the end of the process, the cumulative recrystallized grain area accounted for 28% of the total grain area. The analysis revealed that initially, approximately 70% of the recrystallized grains nucleated adjacent to twin boundaries, with this fraction gradually decreasing as the twin fraction decreased from an initial 15%. 36% of the recrystallized grains not adjacent to twin boundaries were initially observed to form at triple junctions. GOS maps indicated that many grains exhibited GOS values below 1° without undergoing recrystallization, exhibiting only recovery and growth. For the ZX30 alloy deformed to a low strain level (5%) at 200 °C, the present study reveals that the area fraction of grains with GOS below 1° could not be used as the sole metric for quantifying the recrystallized fraction. The total number of recrystallized grains as a function of the angle between the c-axis and the normal direction (ND) was determined, revealing a weakening of the basal texture for the annealed ZX30 alloy.