Keyhole-induced porosity in laser-arc hybrid welded aluminum

Abstract

Keyhole-induced macro-porosity, which results from the collapse of the keyhole that formed by the reaction forces of metal vapors, is a major problem limiting laser and laser-arc hybrid weldability of age-hardenable aluminum alloys, such as AA2024-T3. The mechanism of porosity suggests that the weld metal solidifies more rapidly than the possible rise velocity of the gas bubbles that formed during keyhole collapse, resulting in severe porosity. The porosity behavior of AA2024-T3 during laser-arc hybrid welding was studied using microscopy and X-ray radiography techniques. Porosity-free welding of the alloy is attainable in the conduction mode welding, whereas porosity increased significantly with increased laser intensity during keyhole mode welding. Porosity was mostly severe when the beam was focused at the surface of the workpiece. The laser beam and the arc decouple from each other with increased laser-wire distance, affecting keyhole depth and porosity. In order to control porosity during laser-arc hybrid welding of aluminum alloys, the role of various welding parameters on the material’s response should be balanced with the required weld geometry.