Abstract
The wrought magnesium alloy AZ31B exhibits good weldability and welds with strength levels equaling the strength of the base material are achieved easily. In recent research the focus spot diameter of the laser beam welding application became a tool to gain understanding for the combination of mechanical properties and technological demands, like the gap bridging
capacity for welding without any filler wire by the use of a multi-kW fiber laser. The present study investigated the beam wobbling technique in laser beam welding of AZ31B butt joints. When a wobbling head is used a small circular wobble at high frequency is superimposed to the laser focus spot linear trajectory. As a result a larger apparent spot is obtained, and a larger weld bead produced with enhanced gap bridging capacity and better mechanical properties. With wobbling up to 98.2 % of the base material UTS were
achieved. Overall mechanical properties, such as UTS, AF, and Vickers hardness, were correlated with the microtexture and technological aspects like gap bridging capacity.
With both technologies it was possible to close gaps up to 0.4 mm width, with 50 % of the thickness of sheet. For the linear laser welding this was possible with a focus spot diameter of 1000 μm, while the laser beam wobbling needed a working diameter of 1872 μm.
Smoother weld seam surfaces were obtained with laser beam wobbling. The results offer solutions for the
industrial use of different laser beam welding techniques with certain respect to the cost effectiveness of possible technological applications.
