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Laser Welding of Aluminum Alloys With CO 2 Lasers: Weld Quality and Mechanical Properties
Published September 13, 1993 by ISATA - Dusseldorf Trade Fair in United Kingdom
Event: ISATA 1993
Recently, the application of aluminum alloys in the road and rail vehicle industry has increased rapidly due to the demand for saving weight and, therefore, energy for environmental protection. Especially in the automotive industry big efforts are made to involve aluminum for lightweight constructions and, moreover, this material is preferred because of its high recycling potential.
Although aluminum together with new designing technologies provides many advantages in comparison to steel or plastics, the breakthrough has not appeared, until now. A main reason for this lies in the lack of a suitable fusion-welding process for aluminum alloys. In this context, the laser might be the suitable industrial welding tool as it has proven to be in the case of steel since a couple of years. In the keyhole welding mode, deep weld seams with a low thermal load of the workpiece at high processing speeds can be produced. The achievable welding speed versus plate thickness for single-layer AlMgSil-weldments in welding by today's available high-power CO2 lasers with a total beam power up to 5 kW and for conventional fusion-welding processes is plotted. In the interesting thin- and middle-sheet thickness range up to 8 mm, much higher welding speeds can be obtained by a CO2 laser than by MIG or TIC processes. This is not true for the plasma-arc process, but there the thermal distortion of the welded workpiece is much higher. Due to the necessity of a vacuum chamber, Electron-Beam welding is very large-scaled and inflexible in welding large plain or complex three-dimensional car body structures, whereas the laser beam offers the opportunity of guiding by a gantry or robot system. In contrast to resistance spot welding of aluminum, where the stable oxide skin makes the process unreliable and produces high electrode wear, the high energy dense laser beam interacts contact-free with the workpiece.
Previous studies dealt with the influence of laser beam and processing parameters on the development of the weld seam in laser welding of aluminum alloy sheets. This report presents results of investigations about the weld quality and mechanical properties of bead-on plate and butt-welds of two aluminum alloys of 6xxx- and 5xxx-series in a sheet thickness range between 1 and 5 mm, mainly used in transport vehicle applications. The welds were produced at focusing numbers of 4 and 6 by a 5 kW CO2 laser measuring a beam-quality number of 0.3. Pure He or a gas mixture of 75% He/25% Ar at a gas-flow rate of 2000 l/h was applied for protecting the weld zone by an off-axis Cu-nozzle.