Defect-suppressed extrusion of high-purity magnesium: A processing–structure–defect framework for biodegradable implants

High-purity magnesium is an attractive platform for biodegradable implants because it minimizes risks associated with alloying elements, yet its clinical translation is constrained by poor hot workability and the persistence of casting-derived defects that accelerate mechanical failure and corrosion. Here we establish a processing-structure-defect framework that enables defect-suppressed extrusion of 4N(99.99 wt.%) Mg into rods with structural characteristics relevant to biodegradable implant applications. Processing maps derived from hot-compression experiments and Arrhenius-type constitutive modelling reveal an unusually narrow stability window governed by low strain-rate sensitivity and limited dynamic recrystallization in coarse-grained pure Mg. Guided by this map, low-strain-rate extrusion within dynamic recovery/recrystallization-stable domains promotes pore collapse and spheroidization while avoiding flow instability. As a result, the maximum defect size is reduced to < 60 μm, nearly two orders of magnitude smaller than in commercial high-purity Mg rods. The refined defect state translates into a tensile strength above 190 MPa and an in vitro degradation rate of ∼0.2 mm·year^-1, demonstrating that mechanical integrity and corrosion control can be achieved simultaneously in high-purity Mg. This work therefore offers a scalable and practically accessible route to manufacturing defect-controlled pure Mg rods with structural and degradation characteristics relevant to biodegradable implant applications.