X-ray investigation of melt flow behavior under magnetic stirring regime in laser beam welding of aluminum

The use of magnetic fields to influence weld bead shape and dilution in laser welding of aluminum alloys was recently suggested. It was already demonstrated for the case of laser welding of hot-cracking sensitive aluminum alloys with silicon-containing filler wire that applying alternating magnetic fields has an impact on the dilution of silicon in the melt pool, yielding a sufficient silicon content throughout the weld and allowing to suppress hot-cracking. However, the interaction mechanisms between the aluminum melt and the magnetic field are still subject of current investigations and are not fully revealed yet. The behavior of the melt flow under influence of an external magnetic field can be visualized by microfocused high-speed x-ray transmission imaging. To do so, high density tracer materials such as tin (Sn) and tungsten (W) particles that follow the melt flow are introduced into the base material. It can be seen that the additionally induced forces of the magnetic field cause higher velocities in the melt pool. Moreover, the flow of molten liquid perpendicular to the magnetic field is modified. The experimental results are discussed in light of general theoretical assumptions concerning a liquid metal flow under the influence of an external magnetic field. It is established that the effect of the alternating magnetic field can be explained as an anisotropic pulsating electromagnetic force brake that causes a specific deflection of the liquid metal flow.