Magnetic stirring during laser welding of aluminium

The use of magnetic fields to influence melt flow is a well-established method e.g. in foundry technology. For arc welding processes (especially TIG welding), a process called magnetic stirring was first proposed, patented and investigated in the 1970s. The central aim was to improve (by the help of an alternating magnetic field coaxial with the arc axis) weld quality especially in aluminium by the combined effects of arc current and magnetic field. It was established that such fields indeed are capable of influencing weld bead appearance, of increasing the degree of dilution, of decreasing pore formation and of producing a finer grain structure. However, the process never gained wide industrial acceptance. In the late 1990s, some efforts have been taken to apply constant magnetic fields to laser welding processes, aiming at influencing weld geometry, reducing porosity and potentially increasing welding speed. However, neither have any detailed statements been made on possibilities to influence melt flow and, consequently, filler metal distribution, nor on the application of alternating magnetic fields on laser welding.

To help this situation, basic studies on magnetically influencing melt flow during laser welding of Aluminium have been conducted. To that end, alternating fields have been coaxially applied with magnetic flux densities up to 60 mT and frequencies in the the range of 0 to 20 Hz. It was demonstrated by the help of a specially developed method that, depending on the parameters chosen, such fields indeed are capable of influencing melt flow and weld pool dilution, thus “stirring” the weld metal. The results have been so promising that further investigations will be conducted, also focussing on laser hybrid welding especially of hot-cracking sensitive aluminium alloys.