Initial degradation behavior of as-cast, hot-rolled, and cold-rolled Zn-0.5Mg alloys

Zinc alloys demonstrate superior potential as degradable hard tissue implants by exhibiting an intermediate degradation rate between the sluggish corrosion of iron-based alloys and the excessive degradation of magnesium alloys. The initial degradation dynamics at the alloy-tissue interface critically influences subsequent biological responses. This study systematically investigated the early-stage degradation behavior of Zn-0.5Mg alloys with as-cast, hot-rolled, and cold-rolled states under simulated physiological conditions (0.9% NaCl, 37 ± 0.5 °C), using multi-scale characterization integrating electron back-scattering diffraction (EBSD) and scanning Kelvin probe force microscope. Surface potential heterogeneity drives preferential interfacial degradation at second-phase/matrix boundaries, inducing particle detachment. As-cast, hot-rolled, and cold-rolled Zn–0.5Mg alloys show surface potential heterogeneity of 253 mV, 137 mV, and 110 mV, respectively. Intriguingly, quasi-in-situ EBSD analysis revealed [0001]-oriented second-phase particles in as-cast alloys create localized corrosion-resistant zones, and the segregation of second phases directs degradation propagation along grain boundaries that initiate intergranular corrosion. Conversely, rolled alloys developed intragranular polarized second phases that initiated pitting. The bimodal grain structure in hot-rolled specimens amplified micro-galvanic coupling, leading to a faster degradation rate (4.415×10-6 g·mm-2·d-1) than that of cold-rolled counterparts (3.937×10-6 g·mm-2·d-1). By establishing explicit microstructure-processing-degradation correlations, the critical insights into the rational design of Zn-Mg alloys with spatiotemporally controlled degradation profiles was provided for orthopedic applications.