Ductile fracture behavior of Mg–Zn–Ca alloy in microtube extrusion

This study investigates the ductile fracture behavior of Mg-Zn-Ca alloy microtubes during extrusion. Uniaxial tension, shear, and compression tests were conducted at 250–450 °C to characterize the plastic and fracture properties under various stress states. The failure strain increased with temperature under all tested stress states, with the largest increase occurring between 250 and 350 °C. This temperature dependence was more pronounced under shear loading than under uniaxial tension or compression. To capture the coupled effects of temperature and stress triaxiality on fracture, a damage model was developed using the GISSMO-SAMP framework with a Hosford-Coulomb-based fracture locus. The model was validated by comparing the predicted fracture locations and extrusion outcomes with extrusion experiments conducted at 350–400 °C. The simulations showed that microtube extrusion promotes a local transition of the stress state from compression toward shear near the die entry, which accelerates damage accumulation and leads to ductile fracture. To identify conditions that prevent this failure, processing temperatures and microtube dimensions were systematically varied. Within the investigated process window, the safe zone indicates that processing temperature has a stronger influence on formability than microtube dimensions under high extrusion-ratio conditions.