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<p>This study conducted friction stir welding (FSW) butt joining of 2219-T87 and 7075-H112 aluminum alloys with rotation speeds ranging from 700 to 1000&#xa0;rpm and revealed the effects of rotation speed on grain characteristics, precipitation behavior, geometrically necessary dislocation (GND) density, and mechanical properties via electron backscattered diffraction analysis, transmission electron microscopy, and mechanical tests. The results revealed a significant dependence of grain structure and precipitate characteristics on rotational speeds. As speed increased, the nugget zone (NZ) gained higher heat input, causing grain coarsening and fluctuating recrystallization ratio. Thermo-mechanical processes governed the evolution of precipitates, specifically the strengthening <i>θ</i>′ (Al<sub>2</sub>Cu) in 2219 alloy and <i>η</i>′ (MgZn<sub>2</sub>) in 7075 alloy. At 700-900&#xa0;rpm, thermal effects dominated, causing precipitates dissolution and coarsening. At 1000&#xa0;rpm, severe plastic deformation induced mechanical fragmentation of precipitates, reducing their average size by 27.2% compared to the 900&#xa0;rpm condition. Joint strength increased first and then decreased with increasing rotational speeds, reaching an optimal tensile strength of 336&#xa0;MPa at 900&#xa0;rpm. Fracture analysis confirmed that failure consistently initiated at the interface between the NZ and the advancing-side thermo-mechanically affected zone (AS-TMAZ), where the hardness gradient is most pronounced.</p>

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Effect of Rotational Speeds on Microstructure and Mechanical Properties of 2219/7075 Dissimilar Aluminum Alloy FSW Joints

  • 期刊论文

  • 发表日期：

    2026年8月4日

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  • Peng Chen,
  • Jie Wang,
  • Chenggong Zhao,
  • Hongfei Liao,
  • Xiong Wen,
  • Wenhao Chen,
  • Yang Tang,
  • Bensheng Huang,
  • Zhiqing Zhang

摘要

This study conducted friction stir welding (FSW) butt joining of 2219-T87 and 7075-H112 aluminum alloys with rotation speeds ranging from 700 to 1000 rpm and revealed the effects of rotation speed on grain characteristics, precipitation behavior, geometrically necessary dislocation (GND) density, and mechanical properties via electron backscattered diffraction analysis, transmission electron microscopy, and mechanical tests. The results revealed a significant dependence of grain structure and precipitate characteristics on rotational speeds. As speed increased, the nugget zone (NZ) gained higher heat input, causing grain coarsening and fluctuating recrystallization ratio. Thermo-mechanical processes governed the evolution of precipitates, specifically the strengthening θ′ (Al2Cu) in 2219 alloy and η′ (MgZn2) in 7075 alloy. At 700-900 rpm, thermal effects dominated, causing precipitates dissolution and coarsening. At 1000 rpm, severe plastic deformation induced mechanical fragmentation of precipitates, reducing their average size by 27.2% compared to the 900 rpm condition. Joint strength increased first and then decreased with increasing rotational speeds, reaching an optimal tensile strength of 336 MPa at 900 rpm. Fracture analysis confirmed that failure consistently initiated at the interface between the NZ and the advancing-side thermo-mechanically affected zone (AS-TMAZ), where the hardness gradient is most pronounced.