Optimizing weld morphology and mechanical properties of laser welded Al-Si coated 22MnB5 by surface application of colloidal graphite

Laser welding of tailored blanks made of Al-Si-coated 22MnB5 steel using a filler wire and a variable energy distribution laser optics

“…These results confirm those obtained in the comparison between DoE configurations described before and are substantially aligned with the same observed for HSBM [23]. As observed for hardness values, no significant drops of UTS and total elongation values are observed as in other cases with ferritic FZ microstructures [27,28,39,41]. This confirms one more time the absence of softer ferrite in the weld seam.…”

“…Figure 11 shows the results of hardness tests conducted on samples of configurations "O" and "E." For both configurations, hardness values are included in the range 494-543 HV 0.5 , which are aligned with the typical values for the 22MnB5 HSBM (500-550 HV) [23]. In previous studies, significant drops of hardness of about 40% compared to the BM are detected in the FZ due to the presence of softer ferrite [27,28,39,41]. In this case, the comparison between BM and FZ hardness values highlights variations lower than 5% thanks to the martensitic microstructure of the weld seam.…”

“…Indeed, the additional coating, having a vaporization temperature higher than Al-Si coating, brings an increase of pressure of the underlying coating that finally explodes. This method is effective for bead-on-plate joints with the highest considered thicknesses of graphite coating [41]. Nevertheless, as already observed before, the application and measurement of a coating thickness in the order of 10 −4 ÷ 10 −5 m could be difficult in a real production process with butt joint configuration of different thicknesses sheets.…”

“…Moreover, the solution of an additive Ni surface layer, which has been tested only in bead-on-plate tests [39], could be difficult and time-consuming on butt joints for real industrial applications. Other approaches have been developed trying to eliminate the Al-Si layer without a real decoating procedure but through a preheating treatment [40] or the application of a colloidal graphite coating [41,42]. The former consists in heating the steel sheet prior to laser welding reaching a temperature of 800 °C that allows the evaporation of Al-Si coating but preserves the underlying Fe-Al intermetallic layer [40].…”

Unstable aluminum segregation phenomenon in blind keyhole laser welds of Al-Si coated hot stamping steel

“…For a similar purpose, Lee et al, 2018 used high carbon wire to increase the carbon content to modify the critical aluminum content of phase transformation from liquid to austenite. In addition, Khan et al, 2021 utilized spraying carbon lm on the surface, which resulted in more spatters and higher carbon dissolution. Partial aluminum coating would be removed in the front weld pool.…”