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<p>This study investigates the enhancement of joint strength in AZ91 magnesium alloy using dry ice-cooled friction stir welding (FSW), with a comprehensive focus on microstructural evolution and mechanical performance. Conventional FSW reduced the grain size to approximately 7.5&#xa0;µm and refined the precipitates to about 1.8&#xa0;µm, whereas the untreated AZ91 base alloy exhibited significantly coarser grains (~ 76&#xa0;µm) and larger, clustered precipitates (~ 5.8&#xa0;µm). The use of dry ice cooling during FSW further enhanced mechanical performance, achieving finer precipitates (~ 1.4&#xa0;µm) and more refined grains (~ 4.2&#xa0;µm). X-ray diffraction (XRD) analysis confirmed improved phase stability in the cryogenically processed joints, particularly preserving Mg₁₇Al₁₂ and Al₈Mn₅ phases. Cryogenic FSW significantly increased hardness from 74.5 HV in the base alloy to 94.2 HV in the FSW condition, reaching a maximum of 103.3 HV. Although the base metal maintained the highest ultimate tensile strength (176&#xa0;MPa) and elongation (20.5%), the cryogenic welds achieved near-base strength (165&#xa0;MPa) with reasonable ductility (14.9%). SEM fracture analysis revealed large dimples in the base metal, finer dimples in FSW joints, and ultra-fine dimples in cryogenic welds, indicating enhanced fracture resistance and microstructural refinement. In summary, dry ice-cooled FSW significantly improved joint strength and hardness by promoting grain refinement and phase stability, resulting in high-performance AZ91 welds.</p>

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Improvement of Joint Strength in AZ91 Magnesium Alloy via Dry Ice-Assisted Friction Stir Welding: An In-Depth Analysis of Microstructural and Mechanical Characteristics

  • 期刊论文

  • 发表日期：

    2025年11月4日

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  • Sudhakar Uppada,
  • Gogulamudi Balakrishna,
  • Chitturi Ram Prasad,
  • P. Bhargavi,
  • G. S. V. Seshu Kumar,
  • Ravi Varma Penmetsa,
  • Shahid Tamboli,
  • M. Zubairuddin

摘要

This study investigates the enhancement of joint strength in AZ91 magnesium alloy using dry ice-cooled friction stir welding (FSW), with a comprehensive focus on microstructural evolution and mechanical performance. Conventional FSW reduced the grain size to approximately 7.5 µm and refined the precipitates to about 1.8 µm, whereas the untreated AZ91 base alloy exhibited significantly coarser grains (~ 76 µm) and larger, clustered precipitates (~ 5.8 µm). The use of dry ice cooling during FSW further enhanced mechanical performance, achieving finer precipitates (~ 1.4 µm) and more refined grains (~ 4.2 µm). X-ray diffraction (XRD) analysis confirmed improved phase stability in the cryogenically processed joints, particularly preserving Mg₁₇Al₁₂ and Al₈Mn₅ phases. Cryogenic FSW significantly increased hardness from 74.5 HV in the base alloy to 94.2 HV in the FSW condition, reaching a maximum of 103.3 HV. Although the base metal maintained the highest ultimate tensile strength (176 MPa) and elongation (20.5%), the cryogenic welds achieved near-base strength (165 MPa) with reasonable ductility (14.9%). SEM fracture analysis revealed large dimples in the base metal, finer dimples in FSW joints, and ultra-fine dimples in cryogenic welds, indicating enhanced fracture resistance and microstructural refinement. In summary, dry ice-cooled FSW significantly improved joint strength and hardness by promoting grain refinement and phase stability, resulting in high-performance AZ91 welds.