Substantial improvement of mechanical properties of Zn-Mg alloys to orthopedic implants via rotary swaging.

Abstract

The limited strength of unalloyed zinc (Zn) hinders its use in bone repair, where materials must withstand substantial stress. Rotary swaging (RS) serves as a promising technique to enhance metal performance by modifying their internal microstructures. Herein, Zn-0.5Mg alloys undergo room-temperature RS, with their post-processing characteristics, including microstructural features, mechanical performance, degradation behaviors, and biological responses being systematically examined. Findings demonstrate remarkable microstructural optimization and breakdown of lamellar structure following RS. As strain rise, average grain sizes of cast Zn-0.5Mg alloy reduce progressively from 100 μm to 1.10 μm (RS-2), with complete refinement of second phases. This method remarkably boosts the alloy's ultimate tensile strengths from 163 MPa of cast to 465 MPa of RS-3, while the ductility improved from 2 to 27.8%., satisfying bone implant specifications. Such enhancement stems from multiple mechanisms including grain boundary strengthening, dislocation strengthening, and second phase strengthening. Enhanced processing passes correlate with reduced degradation rates, mainly attributed to diminished localized corrosion from galvanic corrosion between Zn and Mg₂Zn₁₁ compounds. Regarding biological performance, as-swaged Zn-Mg alloys demonstrate superior cellular compatibility and bone-forming potential relative to inert titanium. These outcomes offer important references for developing robust Zn-based materials for skeletal reconstruction applications.