Prevention of coating-induced agglomerations within the weld seam during laser beam deep penetration welding of aluminum-silicon coated press-hardened steel

Press-hardened steels like 22MnB5 (1.5528) have great potential in terms of their use in the field of lightweight construction. However, due to the aluminum-silicon coating, applied for press-hardening, strength-reducing agglomerations can occur within the seam after laser deep penetration welding of already hardened material. To investigate the hypothesis that the agglomeration formation can be reduced by beam modulation strategies, laser deep penetration welding experiments with changing beam modulation strategies such as “transversal”, “circular” and “vertical eight” shaped patterns were carried out using constant welding speed and laser power. After comparing the resulting cross-sections to coated and decoated samples welded without beam modulation, the hypothesis was found to be true in case of all modulation strategies examined as no agglomerations could be detected within the samples. In addition, in case of the beam modulation strategies “circle” and “vertical eight”, the fracture type could be changed from a separation fracture along the melting line to a shear fracture crosswise to the seam in sheet metal plane comparable to the decoated samples.