Laser beam welding of aluminum alloys is becoming of increasing interest with respect to light-weight structures. Compared to welding of steel, the process is rendered difficult by the specific material properties. On the basis of a fundamental understanding of the relevant physical mechanisms, guidelines for a successful conduction of the welding process and quality assurance are presented. Factors relevant for deep penetration threshold, process efficiency, process stability and for achieving high seam quality are discussed. In particular, by the combination of two individual focal spots along or normal to the welding direction a process-adapted distribution of the laser power yields substantial improvements. With respect to quality assurance a new method presented here uses the relationship between the geometry of the keyhole and the emitted laser light to control welding depth and to monitor seam defects.
Welding of Al-Mg and Al-Mg-Si alloys was performed using twin spot beams formed with two Nd: YAG lasers for the purpose of reducing porosities and humping caused due to unstable phenomena of weld bead during welding of aluminum alloys. The relationship between the configuration of the twin spot beam and the quality of the weld beads was investigated using X-ray and high-speed camera observations of the keyhole shapes and weld beads. X-ray observation of the weld beads showed that beam distance had a strong influence on the amount of porosities. At a shorter beam distance, porosities were apt to occurred in the weld. The amount of porosities decreased with an increase of beam distance. Beam distance affects keyhole shapes. The amount of porosities was clearly related to the ratio of keyhole depth to keyhole opening. Larger keyhole opening and/or shallower keyhole depth, smaller amount of porosities caused by instability of the weld pool.
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