Study on Removal Mechanism of blowholes in Straight Polarity Direct Current Tungsten Arc Welding of Aluminum Alloy

鋁合金直流正接鎢極氬弧焊氣孔去除機理研究

Hui Li(栗慧) ； Jun-Shan Yao(姚君山) ； Jia-Sheng Zou(鄒家生)

《中國機械工程學刊》 44卷2期 (2023/04) Pp. 143-153

摘要

2219 aluminum alloy has a series of advantages, such as good mechanical properties, stress corrosion resistance, welding performance, low hot crack tendency, and is widely used in the aerospace field. In the process of evaluating the welding process performance of 2219 aluminum alloy, it was found that the high porosity was proved to be the main weakness of the joint quality of AC TIG welding. The Straight Polarity Direct Current (DCSP) TIG welding process of 2219 aluminum alloy is realized by removing the oxide film on the surface of aluminum alloy with activating flux. The outstanding feature is that the internal porosity of TIG weld is effectively reduced, and the welding quality is improved. Therefore, the mechanism of activating flux to remove the internal porosity of 2219 aluminum alloy DCSP TIG welding was studied. The results show that DCSP TIG welding arc is stable, and the activating flux covers the weld pool surface, which can protect the weld pool and reduce the hydrogen solubility in the weld pool. The infrared thermal imager is used to measure the temperature of the welding joint. The coating of activating flux can increase the heat input of the DCSP TIG welding joint. The increase of the welding heat input reduces the solidification speed of the molten pool, increases the existence time of the molten pool, and hydrogen bubbles have enough time to escape from the molten pool. Through the analysis of the force on the surface of the molten pool, it can be seen that the coating of activating flux increases the heat input of the TIG welding joint. The greater the heat input, the stronger the effect of Lorentz force and plasma force on the molten pool, thus changing the movement direction of the metal in the molten pool, which is conducive to the bubble floating, and effectively inhibits the generation of weld porosity.

關鍵字

DCSP TIG Welding ； A-TIG welding ； weld porosity ； Activating Flux

並列摘要

2219鋁合金具有良好的力學性能、抗應力腐蝕性能、焊接性能，熱裂紋傾向低等一系列的優點，被廣泛應用在航空航太領域。開展2219鋁合金的焊接工藝性能評估過程中發現，氣孔發生率高被證實是交流鎢極氬弧焊（TIG）接頭品質的主要薄弱點。利用活性劑去除鋁合金表面氧化膜實現2219鋁合金的直流正接TIG焊工藝，其突出的特點是有效降低了TIG焊縫內部氣孔，改善了焊接品質。本文研究了活性劑去除2219鋁合金直流正接TIG焊縫內部氣孔的機理。研究結果表明：直流正接TIG焊接電弧穩定，活性劑覆蓋在焊縫熔池表面，可保護熔池，減小氫在熔池中的溶解度。採用紅外熱像儀測量焊接接頭的溫度，塗覆活性劑能增加直流正接TIG焊接頭熱輸入，焊接熱輸入的增大降低了熔池的凝固速度，增加了熔池存在時間，氫氣泡有足夠時間從熔池中逸出。通過對熔池表面受力情況進行分析可知，塗覆活性劑增加了TIG焊接頭熱輸入，熱輸入越大，使洛倫茲力和等離子體力對熔池的作用效果增強，從而改變熔池金屬的運動方向，有利於氣泡浮出，有效抑制了焊縫氣孔的產生。