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<p>This study systematically investigates the microstructural evolution and mechanical properties of AZ91 magnesium alloy during friction stir welding (FSW), focusing on the impact of welding parameters such as rotational and welding speed. The formation of a complex microstructure within the weld zone exerts a significant influence on the mechanical performance of FSW joints. Experiments conducted under varying welding conditions reveal the correlations among processing parameters, grain size in the weld nugget zone (NZ), and mechanical properties, such as yield strength (YS), ultimate tensile strength (UTS), and elongation (EL). Dynamic recrystallization (DRX) occurs during the FSW process, leading to significant grain refinement. Specifically, the grain size of the base metal (BM) is reduced from 34.03 to 4.31&#xa0;μm in the NZ under the optimal welding parameters (1200&#xa0;rpm, 200&#xa0;mm/min). In addition, the grain size in the NZ can be quantitatively described by the empirical relationship: ln(d) = 1.2512 – 0.04816Z. The study also explores the role of dislocation density in plastic deformation and mechanical properties. Dislocations drive deformation, with lattice resistance increasing as dislocation density rises, enhancing YS. While the Hall–Petch relationship suggests finer grains lead to higher YS, experimental results show that, at certain rotational speeds, grain refinement does not always improve YS, UTS, or EL. This indicates that dislocation density significantly affects the mechanical properties of welded joints. This study provides insights into the complex interactions between welding parameters, grain size, and mechanical properties of AZ91 magnesium alloy during FSW, offering guidance for optimizing FSW parameters to achieve superior joint performance.</p>

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Effect of welding conditions on the grain structure, texture, and mechanical properties of friction stir-welded AZ91 magnesium alloy sheet

  • 期刊论文

  • 发表日期：

    2026年7月22日

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  • Zehua Yan,
  • Junbo Zhang,
  • Fangyu Jing,
  • Wei Zhang

摘要

This study systematically investigates the microstructural evolution and mechanical properties of AZ91 magnesium alloy during friction stir welding (FSW), focusing on the impact of welding parameters such as rotational and welding speed. The formation of a complex microstructure within the weld zone exerts a significant influence on the mechanical performance of FSW joints. Experiments conducted under varying welding conditions reveal the correlations among processing parameters, grain size in the weld nugget zone (NZ), and mechanical properties, such as yield strength (YS), ultimate tensile strength (UTS), and elongation (EL). Dynamic recrystallization (DRX) occurs during the FSW process, leading to significant grain refinement. Specifically, the grain size of the base metal (BM) is reduced from 34.03 to 4.31 μm in the NZ under the optimal welding parameters (1200 rpm, 200 mm/min). In addition, the grain size in the NZ can be quantitatively described by the empirical relationship: ln(d) = 1.2512 – 0.04816Z. The study also explores the role of dislocation density in plastic deformation and mechanical properties. Dislocations drive deformation, with lattice resistance increasing as dislocation density rises, enhancing YS. While the Hall–Petch relationship suggests finer grains lead to higher YS, experimental results show that, at certain rotational speeds, grain refinement does not always improve YS, UTS, or EL. This indicates that dislocation density significantly affects the mechanical properties of welded joints. This study provides insights into the complex interactions between welding parameters, grain size, and mechanical properties of AZ91 magnesium alloy during FSW, offering guidance for optimizing FSW parameters to achieve superior joint performance.