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<p>Friction stir welded (FSW) joints between medium-strength 6061 and high-strength 7075 aluminum alloys are widely used in aerospace and automotive industries, where achieving high-quality joints is of great importance. However, studies on the effect of pin length on the microstructure and mechanical properties of 4&#xa0;mm-thick 6061/7075 dissimilar FSW joints remain limited. In this study, butt welding experiments were conducted on 4&#xa0;mm-thick 7075-T6 and 6061-T6 aluminum alloy plates using FSW. The influence of varying pin lengths (2.5, 2.8, 3.0 and 3.5&#xa0;mm) on the microstructures and mechanical properties for the FSW joints was investigated. The results show that pin length significantly affects the metal flow in the stir zone (SZ). As the pin length increases, the average hardness of the weld region initially decreases and then increases, while the tensile strength and elongation of the joints exhibit an opposite trend. The relative difference between the Maximum and minimum tensile strengths is 8.38%. When the pin length is 2.8&#xa0;mm (70% of the plate thickness), a smaller onion ring structure is observed in the SZ (7.68 mm<sup>2</sup>), positioned optimally across the weld. At this pin length, the weld region exhibits the lowest average hardness (98.80&#xa0;HV), along with enhanced metal flow behavior, and achieves a tensile strength and elongation of 207&#xa0;MPa and 2.49%, respectively. These findings provide valuable insights into the optimization for microstructures and properties of 4&#xa0;mm-thick 6061/7075 FSW joints.</p>

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Effect of Tool Pin Length on the Microstructures and Properties of Friction Stir Welded Joints of 4 mm 7075-T6/6061-T6 Aluminum Alloy Plates

  • 期刊论文

  • 发表日期：

    2025年9月15日

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  • Sheng Liu,
  • Yongjun Ren,
  • Zhongxu Luo,
  • Jingqiao Qin,
  • Chen Wang,
  • Xinbin Hu,
  • Wei Long

摘要

Friction stir welded (FSW) joints between medium-strength 6061 and high-strength 7075 aluminum alloys are widely used in aerospace and automotive industries, where achieving high-quality joints is of great importance. However, studies on the effect of pin length on the microstructure and mechanical properties of 4 mm-thick 6061/7075 dissimilar FSW joints remain limited. In this study, butt welding experiments were conducted on 4 mm-thick 7075-T6 and 6061-T6 aluminum alloy plates using FSW. The influence of varying pin lengths (2.5, 2.8, 3.0 and 3.5 mm) on the microstructures and mechanical properties for the FSW joints was investigated. The results show that pin length significantly affects the metal flow in the stir zone (SZ). As the pin length increases, the average hardness of the weld region initially decreases and then increases, while the tensile strength and elongation of the joints exhibit an opposite trend. The relative difference between the Maximum and minimum tensile strengths is 8.38%. When the pin length is 2.8 mm (70% of the plate thickness), a smaller onion ring structure is observed in the SZ (7.68 mm2), positioned optimally across the weld. At this pin length, the weld region exhibits the lowest average hardness (98.80 HV), along with enhanced metal flow behavior, and achieves a tensile strength and elongation of 207 MPa and 2.49%, respectively. These findings provide valuable insights into the optimization for microstructures and properties of 4 mm-thick 6061/7075 FSW joints.