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The keyhole behaviors were observed directly by laser welding experiment with quartz glass. Based on Fresnel absorption of laser beam and multi-reflection combined with volume of fluid (VOF) method, a three-dimensional mathematical model was established to study the role of welding speed on keyhole behaviors and keyhole-induced porosity formation in laser welding of aluminum alloy. The keyhole behaviors and weld pool fluid flow were discussed, and the result shows that, although the welding speed varies, the mechanism of keyhole collapse was similar. However, the keyhole stability at higher welding speed was improved due to reduced weld depth fluctuations, spatter number, keyhole depth to width ratio, and keyhole collapse frequency. Furthermore, the improved keyhole stability impeded the keyhole collapse, and the lower weld depth and solidification rate facilitated bubble escaping from the weld pool easily, which are the main factors for suppression of porosity at higher welding speed. [ABSTRACT FROM AUTHOR]

Hybrid laser-MIG (metal inert gas) welding has not been extensively applied in welding of aluminium alloy with thickness more than 10 mm because of the existence of weld defects and low joint strength. In this study, an original hybrid laser-MIG welding plus MIG welding process was developed. Double-sided hybrid laser-MIG welding method was designed and applied to the welding of 30-mm-thick Al 5083 alloy. The process was then optimized by overlaying a MIG welding upon the weld. Analysis on the weld revealed that the overlaid MIG welding played multiple roles, including making up the bead formations, eliminating the keyhole-induced porosities as well as refining grains. Along the longitudinal direction of the weld, the grains became finer from two fringes to the middle, and the mechanical properties improved accordingly. Compared with MIG welding, the hybrid laser-MIG welding plus MIG welding process showed overwhelming superiorities over the MIG welding, which will be promising in industrial applications. [ABSTRACT FROM AUTHOR]

The droplet escape condition in laser welding is established in this paper. A three-dimensional numerical model is developed to study the weld pool convection and spatter formation at full penetration during the fiber laser welding of 5083 aluminum alloy. It is found that when laser power is 9 kW, the bottom of the keyhole is dynamically opened and closed. When the bottom of the keyhole is closed, the molten metal at the bottom of the back keyhole wall flows upwards along the fusion line. When the bottom of the keyhole is opened, few spatters can be seen around the keyhole at the top surface, two flow patterns exists in the rear part of the keyhole: a portion of molten metal flows upwards along the fusion line, other portion of molten metal flows to the bottom of the keyhole, which promote the spatter formation at the bottom of the keyhole rear wall. [ABSTRACT FROM AUTHOR]

The dynamic behavior of an arc plasma involves the complex heat and mass transfer process in the arc welding process, especially for pulsed gas metal arc welding (P-GMAW). The spectral diagnostics of the arc plasma is essential to both the validation of simulation results and the monitoring and control of the arc welding process. In this article, we studied the dynamic behavior and spatial spectral characteristics of the welding arc during the pulsed gas metal arc welding of the AA5083 aluminum alloy with an ER5183 wire using a high-speed camera and spectrometer. Based on the acquired spectra at different time points of the pulse, we calculated the plasma characteristics using the spectral lines emitted from the shielding gas and the metal vapor. The variation and spectral diagnosis of the arc indicated that the bright region was mainly caused by radiation from the metal vapor, which easily increased at the peak current. The measured arc temperature and electron density were elevated along with the welding current. Moreover, the ratio of metal vapor in the arc plasma also increased due to strengthened evaporation from the electrode. Along the horizontal axis, the arc temperature increased and reached a maximum in the central part of the arc. There was a potential local minimum near the electrode as the current increased. The drop of temperature near the electrode was mainly caused by the rapid evaporation and cooling effects of metal vapor. [ABSTRACT FROM AUTHOR]