Laser welding of Al-Si-coated steels for hot stamping in automotive applications is problematic due to the mixing of the coating layers inside the molten pool that weakens the resulting weld seam. In this case, the most common welding procedure to overcome this issue consists in removing the Al-Si layer through laser ablation prior to the joining. This method continues to be the most widely used by major producers of tailor welded blanks, although in situ ablation of the Al-Si coating can be costly and time consuming. In this work, a novel approach consisting in joining as-received (i.e., not decoated) materials using a filler wire and an innovative variable energy distribution laser optics is introduced and tested on tailor welded blanks made of 22MnB5. Tensile tests of specimens obtained from a 33 full factorial design of experiment have shown an average value of ultimate tensile strength of 1523 MPa, which is much higher than the one usually observed in as-received welded then hot-stamped conditions and aligned with hot-stamped base material values. Hardness test results (494–543 HV0.5) were in the typical hot-stamped base material range of values as well, while SEM–EDS analyses detected no ferrite inclusions inside the fusion zone. Variations of the main process parameters have been considered on an iso-thickness and iso-material configuration, empirically demonstrating the stability and reliability of the proposed methodology as well as its suitability for production purposes.
Temperature-induced strain with, at the same time, reduced formability is, among other things, responsible for crack development in the range of high temperatures. For a more detailed examination of these so-called hot cracks, experimental measurements of the strain during the welding process have been carried out using neutron diffraction. The measurement of strain is important since it exerts decisive influence on the development of cracks.
Laser welding of Al-Si coated steels for hot stamping in automotive applications is problematic due to the mixing of the coating layers inside the molten pool that weakens the resulting weld seam. The most common welding procedure used in this case consists in removing the Al-Si layer through laser ablation prior to the joining. Although in-situ ablation of the Al-Si coating can be costly and time consuming, this method continues to be the most widely used by major producers of tailor welded blanks (TWB). In this work, a novel approach consisting in joining as-received (i.e. not decoated) materials using a filler wire and an innovative variable energy distribution (VED) laser optics is introduced and tested on TWB made of 22MnB5. Specimens obtained from a 33 full factorial design of experiment have shown a mechanical resistance much higher than that observed in as-received welded then hot stamped cases. SEM and hardness analyses have been performed to better investigate the quality of the resulting weld seam. Variations of the main process parameters have been considered on an iso-thickness and iso-material configuration, empirically demonstrating the stability and reliability of the proposed methodology as well as its suitability for production purposes.
Development of hot cracks during welding of austenitic materials is a challenge which must be coped with when a suitable welding method is to be chosen. Boundary conditions about hot crack formation are not sufficiently known yet. One factor is the state of strain during welding. Therefore, strain is determined via neutron diffractometry next to the fusion line during the welding process. This evaluation allows to draw conclusions about the influence of the state of thermal strain on the hot crack formation.
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