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<p>The 2B06/7B04 dissimilar Al alloy structure is increasingly used in aerospace industry, where demanding service conditions place high requirements on fatigue performance. However, the instability of fatigue properties remains a key challenge limiting the broader adoption of refill friction stir spot welding (RFSSW) for these dissimilar alloys. In this study, RFSSW experiments were conducted on 2B06/7B04 Al alloys to systematically examine the influence of plunge depth (PD) on the fatigue behavior of welded joints. The results demonstrate that PD is a critical process parameter governing fatigue performance. Within the tested range, fatigue resistance improved markedly with increasing PD, reaching an optimum at a PD of 1.8&#xa0;mm. In contrast, static tensile strength exhibited a non-monotonic trend, initially increasing and then decreasing with PD. Three primary fatigue failure modes were identified: Nugget pull-out, Upper sheet circumferential fracture, and Lower sheet circumferential fracture. Fatigue cracks frequently initiated at the hook tip, a region prone to stress concentration. The thermo-mechanically affected zone (TMAZ) was identified as the weakest region of the joint, characterized by a transition from deformed grains to fine recrystallized grains. Furthermore, significant changes in the distribution and size of second-phase particles were observed in the TMAZ compared to the base material, making it a preferential path for fatigue crack propagation.</p>

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Effect of the Plunge Depth on Fatigue of 2B06/7B04 Dissimilar Al Alloy RFSSW Joints

  • 期刊论文

  • 发表日期：

    2025年10月27日

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  • Da Zhang,
  • Zhiwei Jia,
  • Jiangtao Xiong,
  • Fangyuan Jiang,
  • Jinglong Li,
  • Wei Guo

摘要

The 2B06/7B04 dissimilar Al alloy structure is increasingly used in aerospace industry, where demanding service conditions place high requirements on fatigue performance. However, the instability of fatigue properties remains a key challenge limiting the broader adoption of refill friction stir spot welding (RFSSW) for these dissimilar alloys. In this study, RFSSW experiments were conducted on 2B06/7B04 Al alloys to systematically examine the influence of plunge depth (PD) on the fatigue behavior of welded joints. The results demonstrate that PD is a critical process parameter governing fatigue performance. Within the tested range, fatigue resistance improved markedly with increasing PD, reaching an optimum at a PD of 1.8 mm. In contrast, static tensile strength exhibited a non-monotonic trend, initially increasing and then decreasing with PD. Three primary fatigue failure modes were identified: Nugget pull-out, Upper sheet circumferential fracture, and Lower sheet circumferential fracture. Fatigue cracks frequently initiated at the hook tip, a region prone to stress concentration. The thermo-mechanically affected zone (TMAZ) was identified as the weakest region of the joint, characterized by a transition from deformed grains to fine recrystallized grains. Furthermore, significant changes in the distribution and size of second-phase particles were observed in the TMAZ compared to the base material, making it a preferential path for fatigue crack propagation.