Synergistic strengthening and microstructural evolution of bioactive glass reinforced AZ91 magnesium composites via friction stir back extrusion and aging treatment

This study investigates the synergistic effects of 45S5 bioactive glass (BG) reinforcement and post-processing aging on the microstructure, mechanical behavior, and corrosion performance of AZ91 magnesium alloy hybrid composites produced via friction stir back extrusion (FSBE). Microstructural analysis revealed that the incorporation of 45S5 particles effectively stabilized fine grains, with average sizes increasing marginally from 25.2 ± 0.8 μm (unaged) to 29.3 ± 0.9 μm after 12 h aging, compared to a more pronounced coarsening from 30.1 ± 1.1 μm to 35.1 ± 0.9 μm in the unreinforced AZ91 alloy. The 45S5 particles promoted particle-stimulated nucleation, accelerating intra-granular β-Mg 17 Al 12 precipitation and increasing the β-phase fraction from 0.11 ± 0.02 to 0.45 ± 0.03 over 12 h, whereas the unreinforced alloy reached only 0.35 ± 0.01. Vickers hardness increased from 70.8 ± 1.7 HV (unaged) to 86.1 ± 1.9 HV (12 h), while yield strength and ultimate tensile strength rose from 205.3 ± 11.3 MPa and 289.2 ± 10.1 MPa to 289.6 ± 10.4 MPa and 332.5 ± 10.3 MPa, respectively. A moderate reduction in elongation was observed due to the presence of rigid BG particles and the progressive formation of β-phase precipitates, which may introduce localized stress concentrations and limit plastic deformation. Electrochemical analysis demonstrated superior corrosion resistance in BG-reinforced composites. The peak-aged sample exhibited the most positive corrosion potential (−0.24 V) and the lowest current density (14.2 μA/cm 2 ), with EIS revealing higher charge-transfer resistance (132.5 Ω cm 2 ) and a uniform passive layer enriched in Ca and P. Overall, the results indicate that the synergistic interaction between FSBE-induced microstructural refinement, controlled precipitation, and BG particle reinforcement leads to significant improvements in mechanical and corrosion performance, despite the minor trade-off in ductility associated with particle addition.