Fatigue strength of hybrid welded 22MnB5 overlap joints

In order to reduce the weight of automotive parts, lightweight materials like the press hardened AlSi coated high strength steel 22MnB5 is used. This steel enables a reduction of wall thicknesses and simultaneously ensures a high stiffness of the part, e.g., the B pillar. The usage of these steels requires suitable joining technologies. Therefore, a laser GMA hybrid welding process for fillet welds in overlap configuration was designed. This process provides high welding velocities and process tolerances against gaps and misalignments. In this case a single-mode fiber laser was used in order to reduce the thermal impact. Due to the fact that the laser focus spot has only a small diameter of 25 mu m, a beam oscillation was used in order to distribute the laser energy over the melt pool width. This paper is focused on the cyclic load tests which were carried out and analyzed by the staircase method. The influences of laser power and oscillation width are dominating, whereas welding velocity and wire velocity have only a minor influence. By analyzing the failure location and crack propagation of specimens after the cyclic load test, the influence of the AlSi coating can be determined. Coating agglomerations at the fusion line of the melt pool are origins of crack initiation. This is attributed to the formation of brittle intermetallic phases.