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<p>This study investigates the microstructural evolution and cryogenic fracture behavior of friction stir welded (FSW) 2195 aluminum–lithium (Al–Li) alloy joints, with emphasis on grain boundary transformation and precipitate instability. The results reveal a progressive increase in the fraction of high-angle grain boundaries and a pronounced weakening of crystallographic texture from the base material to the weld nugget zone, driven by dynamic recrystallization. Strengthening precipitates undergo significant transformation, with T₁ (Al₂CuLi) phases in the base material degraded in the thermo-mechanically affected zone and replaced by θ′ (Al₂Cu) in the weld nugget zone. A distinct softening zone with minimum hardness (~ 92 HV) was identified at the TMAZ/HAZ interface, where tensile fractures consistently initiated under cryogenic conditions. The joints exhibited a mixed ductile–brittle fracture mode, dominated by microvoid coalescence and quasi-cleavage. These findings clarify the mechanism of cryogenic failure in Al–Li alloy FSW joints and provide guidance for enhancing the reliability of aerospace cryogenic structures.</p>

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Grain boundary transformation and precipitate instability governing cryogenic fracture in friction stir welded 2195 Al–Li alloy joints

  • 期刊论文

  • 发表日期：

    2025年12月5日

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  • H. W. Tang,
  • L. Xu,
  • H. Xu

摘要

This study investigates the microstructural evolution and cryogenic fracture behavior of friction stir welded (FSW) 2195 aluminum–lithium (Al–Li) alloy joints, with emphasis on grain boundary transformation and precipitate instability. The results reveal a progressive increase in the fraction of high-angle grain boundaries and a pronounced weakening of crystallographic texture from the base material to the weld nugget zone, driven by dynamic recrystallization. Strengthening precipitates undergo significant transformation, with T₁ (Al₂CuLi) phases in the base material degraded in the thermo-mechanically affected zone and replaced by θ′ (Al₂Cu) in the weld nugget zone. A distinct softening zone with minimum hardness (~ 92 HV) was identified at the TMAZ/HAZ interface, where tensile fractures consistently initiated under cryogenic conditions. The joints exhibited a mixed ductile–brittle fracture mode, dominated by microvoid coalescence and quasi-cleavage. These findings clarify the mechanism of cryogenic failure in Al–Li alloy FSW joints and provide guidance for enhancing the reliability of aerospace cryogenic structures.