Product Code: ICA13_1505

Effects of Dual-Beam Laser Welding and Pulse Shaping on Cracking Susceptibility of Aa 5754 Aluminum
Authors:
Martin Stambke, Ilmenau University of Technology; Ilmenau Germany
Jean Pierre Bergmann, Ilmenau University of Technology; Ilmenau Germany
Martin Bielenin, Ilmenau University of Technology; Ilmenau Germany
Philipp von Witzendorff, Laser Zentrum Hannover e.V.; Hannover Germany
Presented at ICALEO 2013

Aluminum alloys show a high tendency to the formation of hot cracks during pulsed laser welding, which can be attributed to relatively high thermal expansions, its large change in volume during solidification and its wide solidification temperature range. In order to overcome these disadvantages, a pulsed Nd:YAG laser can be superimposed with a continuous wave diode laser, supporting the welding process. Due to the changed temperature cycle, the solidification conditions can be controlled and hot cracks will be avoided. Additionally both laser spots can be adjusted in their relative position to each other, so that different thermal regimes can be realized. Furthermore it is possible to vary the geometry of the diode laser spot, so that different temperature fields can be obtained.
In these investigations, various geometries of the diode laser spot are studied, such as ring spot, line spot and circular ring spot. The results clearly show that by means of the diode laser crack-free welds can be realized. Using a central arrangement of the ring spot to the Nd:YAG Spot hot-cracking could be avoided, at a power of 300 W. Whereas using a line spot only 200 W were needed to produce crack-free welds.
Another focus of this study was to determine the influence of different cooling gradients during pulsed laser welding. By means of a defined change in the pulse shape the temperature gradient in the melt pool can be controlled directly, so that the solidification process can be adapted to the material behavior. Outgoing of a conventional rectangular pulse, the influence of the cooling slope gradient on the hot crack susceptibility was examined. It was observed that with decreasing temperature gradient hot cracking could be minimized and avoided completely.