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<p>This study challenges the conventional use of adiabatic backplates in micro friction stir welding (µFSW) by demonstrating the superiority of a high-conductivity steel backplate for joining 0.8&#xa0;mm H62 brass sheets. Compared to a traditional asbestos backplate, the steel plate induced rapid cooling, lowering the average weld zone temperature by 115&#xa0;°C. This thermal management constrained plastic material flow, resulting in a significantly finer and more uniform grain structure in the weld nugget, with a higher fraction of low-angle grain boundaries. This microstructural refinement produced exceptional mechanical properties. The steel-backed joint achieved a tensile strength and elongation of 98.3 and 80.87% relative to the base material (BM), respectively—far exceeding the performance of the asbestos-backed joint (82.0% strength, 63.4% elongation). Critically, the steel backplate shifted the failure location from the softened weld nugget (observed with asbestos) to the base material interface, confirming a joint stronger than the parent metal and exhibiting a ductile fracture mode. Conversely, the asbestos plate created a wide, weakened nugget that failed prematurely. In conclusion, employing a high-conductivity backplate is a powerful strategy to optimize thermo-mechanical conditions in µFSW. By regulating heat and promoting grain refinement, this method provides a simple and effective pathway to achieving superior joint performance in thin metallic sheets.</p>

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Influence of Backing Plate Thermal Conductivity on the Microstructure and Mechanical Properties of Micro-Friction Stir Welded H62 Brass Thin-Sheet Joints

  • 期刊论文

  • 发表日期：

    2026年2月9日

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  • Changqing Zhang,
  • Yaxiong Wang,
  • Lintu Zhang,
  • Guoliang Wei,
  • Zhongke Zhang,
  • Yu Ni,
  • Pengsheng Zhang

摘要

This study challenges the conventional use of adiabatic backplates in micro friction stir welding (µFSW) by demonstrating the superiority of a high-conductivity steel backplate for joining 0.8 mm H62 brass sheets. Compared to a traditional asbestos backplate, the steel plate induced rapid cooling, lowering the average weld zone temperature by 115 °C. This thermal management constrained plastic material flow, resulting in a significantly finer and more uniform grain structure in the weld nugget, with a higher fraction of low-angle grain boundaries. This microstructural refinement produced exceptional mechanical properties. The steel-backed joint achieved a tensile strength and elongation of 98.3 and 80.87% relative to the base material (BM), respectively—far exceeding the performance of the asbestos-backed joint (82.0% strength, 63.4% elongation). Critically, the steel backplate shifted the failure location from the softened weld nugget (observed with asbestos) to the base material interface, confirming a joint stronger than the parent metal and exhibiting a ductile fracture mode. Conversely, the asbestos plate created a wide, weakened nugget that failed prematurely. In conclusion, employing a high-conductivity backplate is a powerful strategy to optimize thermo-mechanical conditions in µFSW. By regulating heat and promoting grain refinement, this method provides a simple and effective pathway to achieving superior joint performance in thin metallic sheets.