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<p>Selective laser melting (SLM) enables the fabrication of complex AZ91D magnesium alloy implants, yet clinical applications are hindered by non-equilibrium microstructures and a compromised strength–corrosion balance. This study investigates the effects of T6 heat treatment on the microstructural, mechanical, corrosion, and biological properties of SLM-fabricated AZ91D. Results show that T6 triggers dynamic competition between continuous and discontinuous precipitation of the <i>β</i>-Mg<sub>17</sub>Al<sub>12</sub> phase. Concurrently, Mg-Al diffusion rate disparities induce the Kirkendall effect, forming microvoids. The T6 + 6&#xa0;h sample achieved peak mechanical properties (yield strength 219&#xa0;MPa and ultimate compressive strength 431&#xa0;MPa) via robust Orowan strengthening from dense nanoscale <i>β</i> precipitates. However, prolonged aging deteriorated corrosion resistance. This is driven by discrete <i>β</i> particles acting as micro-galvanic cathodes and the intrinsic porosity of the native oxide film (Pilling–Bedworth ratio = 0.81), which easily ruptures under cathodic hydrogen evolution. Cytotoxicity assays confirmed excellent biocompatibility; human umbilical vein endothelial cells (HUVECs) maintained &gt; 80% viability in 100% extracts and proliferated significantly at diluted concentrations. This pro-proliferation is attributed to a controlled degradation rate mitigating early-stage alkaline stress and optimizing the local microenvironment. This study provides crucial mechanistic insights for optimizing post-treatments of additively manufactured biodegradable magnesium implants.</p>

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Microstructural Evolution and Degradation Mechanisms of SLM AZ91D Magnesium Alloy Subjected to T6 Heat Treatment

  • 期刊论文

  • 发表日期：

    2026年7月29日

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  • Zhiwei Zhang,
  • Qiujun Hu,
  • Chang Chen,
  • Mingsi Deng,
  • Xin Chu,
  • Yilong Dai

摘要

Selective laser melting (SLM) enables the fabrication of complex AZ91D magnesium alloy implants, yet clinical applications are hindered by non-equilibrium microstructures and a compromised strength–corrosion balance. This study investigates the effects of T6 heat treatment on the microstructural, mechanical, corrosion, and biological properties of SLM-fabricated AZ91D. Results show that T6 triggers dynamic competition between continuous and discontinuous precipitation of the β-Mg17Al12 phase. Concurrently, Mg-Al diffusion rate disparities induce the Kirkendall effect, forming microvoids. The T6 + 6 h sample achieved peak mechanical properties (yield strength 219 MPa and ultimate compressive strength 431 MPa) via robust Orowan strengthening from dense nanoscale β precipitates. However, prolonged aging deteriorated corrosion resistance. This is driven by discrete β particles acting as micro-galvanic cathodes and the intrinsic porosity of the native oxide film (Pilling–Bedworth ratio = 0.81), which easily ruptures under cathodic hydrogen evolution. Cytotoxicity assays confirmed excellent biocompatibility; human umbilical vein endothelial cells (HUVECs) maintained > 80% viability in 100% extracts and proliferated significantly at diluted concentrations. This pro-proliferation is attributed to a controlled degradation rate mitigating early-stage alkaline stress and optimizing the local microenvironment. This study provides crucial mechanistic insights for optimizing post-treatments of additively manufactured biodegradable magnesium implants.