A novel welding method for improving weld quality via bypass microhole high-density airflow assist

In this paper, the bypass microhole high-density airflow (BMHA) was innovatively introduced into the welding of 4047 Al alloy for enhancing weld quality. The arc morphology, macrostructure, microstructure and tensile behavior of the weld were investigated. After applying the bypass airflow, the arc gradually transformed from a bell shape into a long cone. When the bypass airflow acted on the arc and the molten pool at a certain blowing angle and air flow rate, the protective gas hood originating from the bypass airflow can suppress the oxidization behavior of the molten pool during solidification process, accompanied by an increase in melting width under higher stiffness bypass airflow. Additionally, with the introduction of BMHA, the microstructure of weld refined through the combined action of cooling and impact stirring, thereby enhancing the tensile strength significantly. Ordinary MIG Al alloy weld mainly fractured between the weld and base metal. In contrast, the proportion of weld area in the fracture gradually decreased after introducing the bypass protective gas, which also indicates an improvement in tensile strength of weld. However, the implement of bypass airflow in front of the arc can severely disturb the protective atmosphere, introducing numerous pores into the weld and causing serous oxidization on the surface, which undoubtedly deteriorates the mechanical properties of the welds. This study provides a novel perspective for improving weld quality, especially for multi-layer and multi-pass welding processes.