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.

Overview of laser-welded thin-walled joints fatigue performance and a statistical method for defect analysis

“…The keyhole cavity starts to form when the laser beam's energy is absorbed in the contact area, and the weldable material starts to melt. When a sucient amount of heat is conducted to the metallic material, atomic bonds break, further generating plasma of vaporised metal atoms and surrounding gases, when electrons are removed [18]. The energy density needs to be around 1 M W/cm 2 for deep penetrating welding [9,10].…”

“…Welding forms a molten pool, which when solidied, forms a welding joint. The keyhole is held open by the recoil pressure of evaporation particles in the keyhole, where the molten pool hydrostatic pressure tends to close the keyhole [18]. Laser welding involves multiple physical phenomena, starting from absorption of the surface, metal melting, keyhole formation, keyhole plasma formation, laser plasma interaction, liquid pressure, plasma interaction, metal solidication etc., which eect the quality of weld and thus fatigue properties [20].…”

“…The stability of the keyhole and the molten pool prescribe how well the welding succeeded. The stability is dependent on two major forces aecting the keyhole region: ablation pressure (or recoil pressure) and the forces and pressures developed by the molten pool [9,18]. In additional to hydrostatic pressure, the surface tension of the molten pool eect on the pressure tend to close the keyhole.…”

Optimization of welding parameters on pores migration in Laser-GMAW of 5083 aluminum alloy based on response surface methodology

“…Zhang [6] believed that Laser-CMT hybrid welding can improve the stability of the laser welding and reduce the porosity in the weld. Ola and Doern [7] pointed out that the laser-arc distance could affect the pores defects. Nielsen [8] believed that laser hybrid welding was suitable for thick workpieces welding, compared with Laser welding, it has lower requirements for welding assemblage.…”

Control of Porosity and Spatter in Laser Welding of Thick AlMg5 Parts Using High-Speed Imaging and Optical Microscopy

“…Moreover, due to its high thermal diffusivity, the weld fusion and penetration are more difficult to achieve in comparison to steel [9]. The fast heat exchange implies also a fast solidification that leads to high stresses, resulting in cracks, pores formation or even complete break of the welded area [10][11][12][13][14].…”