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<p>The manufacturing of large-scale monolithic aluminum alloy structures using friction-stir welded (FSW) tailor-welded blanks (TWBs) has gained significant attention. However, the formability of TWBs is a major concern due to non-uniform material properties around the stir zone (SZ). In this study, cupping tests were conducted on 2024-O aluminum alloy FSW TWBs to evaluate the formability of both as-welded and annealed TWBs. The impact of macroscopic and microstructural characteristics of the stir zone (SZ) during welding and annealing processes on the formability of TWBs was thoroughly investigated. The experimental results revealed that the formability of as-welded TWBs was relatively poor, with a cupping value approximately 50–60% of that of the base metal (BM). This phenomenon was primarily attributed to significantly higher hardness in the SZ compared to other regions of the weld zone, leading to severe mechanical property non-uniformity and decreased formability. Additionally, the upward migration of the bottom ALCLAD layer and the distribution characteristics of the “S” line were identified as crucial factors influencing the formability of as-welded TWBs. On the other hand, after annealing treatment, the formability of TWBs was improved, with the maximum cupping value reaching 90% of BM for the 800-200 TWBs annealed at 340 °C for 2 h. This improvement was attributed to the reduced difference in hardness between the SZ and other regions of the TWBs, resulting in more uniform material properties. The increase of hardness in SZ in as-welded TWBs was caused by the solid solution of the S phase, while the decrease of hardness in SZ in annealed TWBs was due to the nucleation and growth of the S phase. Furthermore, finite element simulation was employed to investigate the stress and strain variations in the SZ, heat-affected zone (HAZ), and BM during the cupping process of TWBs. The simulation results indicated that in as-welded TWBs, the maximum stress was located in the SZ, and the maximum value of equivalent plastic strain (PEEQ) was observed at the interface between the SZ and HAZ. For annealed TWBs, the maximum stress values were found in the SZ, HAZ, and BM, with the maximum PEEQ value occurring in the HAZ. The position of the maximum PEEQ value correlated with the location of observed cracks. This work provides valuable theoretical and experimental foundations for the application of TWBs in critical aerospace fields.</p>

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Formability of friction stir welded 2024-O aluminum alloy tailor-welded blanks: effects of welding parameters and post-weld annealing

  • 期刊论文

  • 发表日期：

    2025年6月16日

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  • Changshu He,
  • Hanwen Zhou,
  • Hao Zhang,
  • Jingxun Wei,
  • Xiaodan Li,
  • Gaowu Qin

摘要

The manufacturing of large-scale monolithic aluminum alloy structures using friction-stir welded (FSW) tailor-welded blanks (TWBs) has gained significant attention. However, the formability of TWBs is a major concern due to non-uniform material properties around the stir zone (SZ). In this study, cupping tests were conducted on 2024-O aluminum alloy FSW TWBs to evaluate the formability of both as-welded and annealed TWBs. The impact of macroscopic and microstructural characteristics of the stir zone (SZ) during welding and annealing processes on the formability of TWBs was thoroughly investigated. The experimental results revealed that the formability of as-welded TWBs was relatively poor, with a cupping value approximately 50–60% of that of the base metal (BM). This phenomenon was primarily attributed to significantly higher hardness in the SZ compared to other regions of the weld zone, leading to severe mechanical property non-uniformity and decreased formability. Additionally, the upward migration of the bottom ALCLAD layer and the distribution characteristics of the “S” line were identified as crucial factors influencing the formability of as-welded TWBs. On the other hand, after annealing treatment, the formability of TWBs was improved, with the maximum cupping value reaching 90% of BM for the 800-200 TWBs annealed at 340 °C for 2 h. This improvement was attributed to the reduced difference in hardness between the SZ and other regions of the TWBs, resulting in more uniform material properties. The increase of hardness in SZ in as-welded TWBs was caused by the solid solution of the S phase, while the decrease of hardness in SZ in annealed TWBs was due to the nucleation and growth of the S phase. Furthermore, finite element simulation was employed to investigate the stress and strain variations in the SZ, heat-affected zone (HAZ), and BM during the cupping process of TWBs. The simulation results indicated that in as-welded TWBs, the maximum stress was located in the SZ, and the maximum value of equivalent plastic strain (PEEQ) was observed at the interface between the SZ and HAZ. For annealed TWBs, the maximum stress values were found in the SZ, HAZ, and BM, with the maximum PEEQ value occurring in the HAZ. The position of the maximum PEEQ value correlated with the location of observed cracks. This work provides valuable theoretical and experimental foundations for the application of TWBs in critical aerospace fields.