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<p>Gas tungsten arc welding (GTAW) has been criticized for its shallow depth of fusion, small deposition rate and low productivity. In this study, in order to improve the quality of GTAW welding, alternating protective airflow (APA) was innovatively introduced into the repair of Al–Cu–Ni alloys by GTAW. The macrostructure, microstructure and mechanical properties of the repaired zone were analyzed and compared to those obtained with traditional pure Ar gas feeding. The effect of alternating argon and helium gas supply on the arc as well as the molten pool was also explored. Results indicate that Ar, He two different properties of the gas alternately into the arc atmosphere so that the arc characteristics of the periodic changes. Compared with He arc, Ar arc pressure is greater, arc voltage is low, heat input is smaller, the arc is more stable, can quickly melt the shallow layer of the alloy surface, He arc compared to the Ar arc morphology contraction, arc temperature is higher, penetration is stronger, can penetrate the shallow layer of the alloy surface and then melt the deep layer. The alternating action of the two arcs, together with the impact of the gas flow, produces a shock effect in the molten pool, causing the Marangoni effect, which promotes the escape of air holes and increases the melting depth-to-width ratio (H/B). Compared to conventional gas delivery, this method effectively stirs the molten pool, disrupting dendrites and promoting nucleation. Consequently, the grains in the repair area recrystallize and form large-angle, stable crystal structures, leading to significant grain refinement. The average grain size is reduced to 40.1&#xa0;<i>μ</i>m. The precipitation phases are the same for both gas delivery methods, and both are <i>γ</i>-Al<sub>7</sub>Cu<sub>4</sub>Ni, <i>δ</i>-Al<sub>3</sub>CuNi, and (<i>θ</i>/<i>θ</i>′)-Al<sub>2</sub>Cu. However, alternating argon and helium gas delivery increases the solidification rate and improves the problem of elemental segregation in conventional gas delivery. At 300&#xa0;°C, the repaired area's of Ar–He alternate gas deliverytensile strength reaches 179&#xa0;MPa, which is 30&#xa0;MPa higher than that achieved with conventional gas delivery methods. The yield strength reaches 145&#xa0;MPa, with an elongation of 9.7&#xa0;pct. The study demonstrates a new method to optimize the macrostructure, microstructure and mechanical properties of the repair zone after arc remelting of Al–Cu–Ni alloys by changing the GTAW gas feeding process.</p>

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GTAW Repair of Near-Surface Defects in Al–Cu–Ni Nacelles Based on Ar–He Alternating Protective Gas: Mechanism of the Effect of Alternating Gas Delivery on Microstructure

  • 期刊论文

  • 发表日期：

    2025年3月5日

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  • GuanLin Feng,
  • HongBin Dai,
  • Fang Liu,
  • Hongwei Zhao,
  • Chaoxiang Chang,
  • Han Jia

摘要

Gas tungsten arc welding (GTAW) has been criticized for its shallow depth of fusion, small deposition rate and low productivity. In this study, in order to improve the quality of GTAW welding, alternating protective airflow (APA) was innovatively introduced into the repair of Al–Cu–Ni alloys by GTAW. The macrostructure, microstructure and mechanical properties of the repaired zone were analyzed and compared to those obtained with traditional pure Ar gas feeding. The effect of alternating argon and helium gas supply on the arc as well as the molten pool was also explored. Results indicate that Ar, He two different properties of the gas alternately into the arc atmosphere so that the arc characteristics of the periodic changes. Compared with He arc, Ar arc pressure is greater, arc voltage is low, heat input is smaller, the arc is more stable, can quickly melt the shallow layer of the alloy surface, He arc compared to the Ar arc morphology contraction, arc temperature is higher, penetration is stronger, can penetrate the shallow layer of the alloy surface and then melt the deep layer. The alternating action of the two arcs, together with the impact of the gas flow, produces a shock effect in the molten pool, causing the Marangoni effect, which promotes the escape of air holes and increases the melting depth-to-width ratio (H/B). Compared to conventional gas delivery, this method effectively stirs the molten pool, disrupting dendrites and promoting nucleation. Consequently, the grains in the repair area recrystallize and form large-angle, stable crystal structures, leading to significant grain refinement. The average grain size is reduced to 40.1 μm. The precipitation phases are the same for both gas delivery methods, and both are γ-Al7Cu4Ni, δ-Al3CuNi, and (θ/θ′)-Al2Cu. However, alternating argon and helium gas delivery increases the solidification rate and improves the problem of elemental segregation in conventional gas delivery. At 300 °C, the repaired area's of Ar–He alternate gas deliverytensile strength reaches 179 MPa, which is 30 MPa higher than that achieved with conventional gas delivery methods. The yield strength reaches 145 MPa, with an elongation of 9.7 pct. The study demonstrates a new method to optimize the macrostructure, microstructure and mechanical properties of the repair zone after arc remelting of Al–Cu–Ni alloys by changing the GTAW gas feeding process.