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<p>The current study examines the effects of multi-pass friction stir processing (FSP) with 100% overlap on the microstructural evolution, surface modification, and damping behavior of AZ61 magnesium alloy. Three passes were made at 1100&#xa0;rpm and 40&#xa0;mm/min with an H13 steel tool to assess the effects of cumulative thermal-mechanical cycling. Optical microscopy showed a transition from coarse as-cast grains to fine equiaxed structures. The second pass resulted in the smallest grain size (4.2&#xa0;μm) due to enhanced dynamic recrystallization and Zener pinning. Scanning electron microscopy (SEM) analysis confirmed the presence of fine β-Mg₁₇Al₁₂ and Mg-Al-Zn precipitates, whose uniform distribution improved grain stability. X-ray diffraction (XRD) revealed the retention of the α-Mg phase with refined intermetallic dispersion. In the second pass, surface hardness (≈ 109 VHN) and compressive stress (~ 900&#xa0;MPa) reached their highest levels, indicating optimal grain refinement and dislocation density. Damping analysis revealed that the second pass had the highest energy dissipation, which was attributed to enhanced grain boundary sliding and dislocation-based mechanisms. The study reveals strong correlations between microstructure, residual stress, and damping performance, highlighting second-pass FSP as the optimal condition for enhancing mechanical stability and vibration resistance in AZ61 alloys.</p>

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Influence of multi-pass friction stir processing on microstructural homogeneity, residual stress gradients, and damping performance of AZ61 magnesium alloy

  • 期刊论文

  • 发表日期：

    2026年3月23日

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  • N. Raghu Ram,
  • K. Sivaji Babu,
  • B. Bala Krishna

摘要

The current study examines the effects of multi-pass friction stir processing (FSP) with 100% overlap on the microstructural evolution, surface modification, and damping behavior of AZ61 magnesium alloy. Three passes were made at 1100 rpm and 40 mm/min with an H13 steel tool to assess the effects of cumulative thermal-mechanical cycling. Optical microscopy showed a transition from coarse as-cast grains to fine equiaxed structures. The second pass resulted in the smallest grain size (4.2 μm) due to enhanced dynamic recrystallization and Zener pinning. Scanning electron microscopy (SEM) analysis confirmed the presence of fine β-Mg₁₇Al₁₂ and Mg-Al-Zn precipitates, whose uniform distribution improved grain stability. X-ray diffraction (XRD) revealed the retention of the α-Mg phase with refined intermetallic dispersion. In the second pass, surface hardness (≈ 109 VHN) and compressive stress (~ 900 MPa) reached their highest levels, indicating optimal grain refinement and dislocation density. Damping analysis revealed that the second pass had the highest energy dissipation, which was attributed to enhanced grain boundary sliding and dislocation-based mechanisms. The study reveals strong correlations between microstructure, residual stress, and damping performance, highlighting second-pass FSP as the optimal condition for enhancing mechanical stability and vibration resistance in AZ61 alloys.