Impact of Aging Conditions and Glass Reinforcement on Microstructural and Mechanical Features of <scp>AZ91</scp> Composites

ABSTRACT This work explores the effect of bioactive glass (BG) reinforcement and aging treatment on the microstructure and mechanical performance of AZ91 magnesium alloy processed by friction stir back extrusion (FSBE). BG particles with an average diameter of 4.62 μm, synthesized via the sol–gel route, were incorporated at 2 and 4 vol.% into AZ91 billets prior to FSBE at 1200 rpm, 40 mm/min traverse speed, and an extrusion ratio of 2.86. Solution heat treatment at 450°C for 3 h, followed by aging at 180°C for 6 and 12 h, was applied to study precipitation behavior and property evolution. FSBE processing refined the microstructure through dynamic recrystallization, while BG particles further stabilized fine grains by Zener pinning and promoted heterogeneous nucleation of β‐Mg 17 Al 12 . Aging for 12 h yielded the most significant property enhancement. The Vickers hardness increased from 66.3 ± 1.2 HV in the solution‐treated alloy to 83.2 ± 0.9 HV with 4 vol.% BG after aging. Similarly, yield strength rose from 181.2 ± 8.4 MPa to 267.6 ± 12.7 MPa, and ultimate tensile strength improved from 252.7 ± 9.1 MPa to 342.1 ± 12.3 MPa under the same conditions. Ductility decreased moderately from 9.1% ± 1.4% to 6.2% ± 1.2% with BG addition and extended aging, reflecting a trade‐off between strength and plasticity. Fractography revealed a transition from ductile dimpled morphologies in the solution‐treated alloy to mixed ductile–brittle fracture in BG‐reinforced and aged specimens, attributed to particle–matrix debonding and precipitation‐induced cleavage.