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<p>This study investigates the microstructural evolution and mechanical performance of AA6061-based hybrid nanocomposites reinforced with graphene nanoplatelets (GNPs) and yttrium oxide (Y₂O₃) fabricated via stir–squeeze casting. Four compositions—unreinforced AA6061 and three hybrid variants with varying reinforcement ratios up to 3 wt.% each—were examined using OM, SEM–EDS, and XRD. The results confirmed uniform dispersion of reinforcements with fine, equiaxed grains, clean grain boundaries and precipitate morphologies. The average grain size decreased from 9.2&#xa0;µm (unreinforced) to 5.5&#xa0;µm (3 wt.% GNP + 3 wt.% Y₂O₃) due to particle-stimulated nucleation and grain-boundary pinning. The highest density (2.720&#xa0;g/cm<sup>3</sup>) and lowest porosity (1.61%) were achieved in the hybrid nanocomposite with equal GNP and Y₂O₃ contents. The addition of Y<sub>2</sub>O<sub>3</sub> in equal weight percent to GNPs helped suppress agglomeration at grain boundaries, while its high-density improved the overall nanocomposite density. Mechanical properties improved substantially: microhardness increased by 60% (72 → 115 HV), ultimate tensile strength by 89% (135 → 255&#xa0;MPa), and yield strength by 152% (78 → 197&#xa0;MPa), accompanied by a moderate ductility reduction (11 → 6.2%). Increasing reinforcement content and GNPs were found to be more effective for enhancing microhardness and tensile properties of nanocomposites. Strength enhancement was attributed primarily to Orowan looping, Hall–Petch grain refinement, and load transfer. XRD confirmed stable Al, GNP, and Y₂O₃ phases without undesirable reactions. Fractographic analysis revealed a transition from ductile to mixed-mode fracture with increased reinforcement. The results demonstrate that equal proportions of GNP and Y₂O₃ yield a dense, defect-free AA6061 hybrid nanocomposite with superior strength-to-weight ratio, suggesting its potential for aerospace and automotive structural applications.</p>

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Microstructural Evolution and Mechanical Properties of Stir–Squeeze Cast AA6061–GNP–Y2O3 Hybrid Nanocomposites

  • 期刊论文

  • 发表日期：

    2026年1月8日

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  • Ashutosh Kumar,
  • Vikas Upadhyay,
  • Chaitanya Sharma

摘要

This study investigates the microstructural evolution and mechanical performance of AA6061-based hybrid nanocomposites reinforced with graphene nanoplatelets (GNPs) and yttrium oxide (Y₂O₃) fabricated via stir–squeeze casting. Four compositions—unreinforced AA6061 and three hybrid variants with varying reinforcement ratios up to 3 wt.% each—were examined using OM, SEM–EDS, and XRD. The results confirmed uniform dispersion of reinforcements with fine, equiaxed grains, clean grain boundaries and precipitate morphologies. The average grain size decreased from 9.2 µm (unreinforced) to 5.5 µm (3 wt.% GNP + 3 wt.% Y₂O₃) due to particle-stimulated nucleation and grain-boundary pinning. The highest density (2.720 g/cm3) and lowest porosity (1.61%) were achieved in the hybrid nanocomposite with equal GNP and Y₂O₃ contents. The addition of Y2O3 in equal weight percent to GNPs helped suppress agglomeration at grain boundaries, while its high-density improved the overall nanocomposite density. Mechanical properties improved substantially: microhardness increased by 60% (72 → 115 HV), ultimate tensile strength by 89% (135 → 255 MPa), and yield strength by 152% (78 → 197 MPa), accompanied by a moderate ductility reduction (11 → 6.2%). Increasing reinforcement content and GNPs were found to be more effective for enhancing microhardness and tensile properties of nanocomposites. Strength enhancement was attributed primarily to Orowan looping, Hall–Petch grain refinement, and load transfer. XRD confirmed stable Al, GNP, and Y₂O₃ phases without undesirable reactions. Fractographic analysis revealed a transition from ductile to mixed-mode fracture with increased reinforcement. The results demonstrate that equal proportions of GNP and Y₂O₃ yield a dense, defect-free AA6061 hybrid nanocomposite with superior strength-to-weight ratio, suggesting its potential for aerospace and automotive structural applications.