Effect of keyhole mode on weld shape and mechanical properties of thin sheets of Al-Si coated 22MnB5 steel

Abstract

The great change of plasma or plumes and weld pool flows existed between “blind” keyhole and open keyhole, especially for thin sheets. The keyhole mode could be changed by increasing the power density for deeper keyhole penetration. In this study, weld shape, aluminum content, δ ferrite fraction, and tensile strength were investigated in laser welding Al-Si coated steel. “Blind” keyhole led to “Y” weld shape, lower aluminum content, less δ ferrite, and higher strength at the optimized parameter. On the contrary, open keyhole led to “X” weld shape, higher aluminum content, more δ ferrites, and lower strength. The microstructure was more homogeneous in low speed “Y” weld. From the high speed images, the open keyhole was accompanied with fierce molten flow on the bottom side. The bottom coating was also important in the aluminum increase. In the suitable combination of welding parameters for “blind” keyhole, their strength could reach the level of decoated sample with no need for decoating preparation.

Recent advances in mitigating fusion zone softening during laser welding of Al-Si coated 22MnB5 press-hardened steels

“…Lin et al [79] conducted a study to examine the influence of laser power and travel speed on the characteristics of the keyhole, as well as the resultant geometry of the FZ. The investigation aimed to determine how variations in laser power and travel speed affect the shape and size of the keyhole, which subsequently impacts the overall geometry of the FZ.…”

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

“…Other interesting approaches consist in enlarging the laser spot on the workpiece surface through beam defocusing [43], the use of optics with higher focal length [44], with particular beam modules, e.g., collateral dual-beam module [45], or with a laser beam oscillation [46,47]. In addition, a characteristic Y-shaped weld section, instead of the common X-shaped (or hourglass-shaped) FZ, could be achieved through beam defocusing [43] or setting the process parameters in the narrow range of values that allows to weld in the particular closed (or blind) keyhole condition [48,49]. Indeed, the weld pool resulting from laser welding with closed keyhole experiences less fierce flows than the one with open keyhole due to the tighter width of the flow channel around the lower part of the keyhole.…”

“…Indeed, the weld pool resulting from laser welding with closed keyhole experiences less fierce flows than the one with open keyhole due to the tighter width of the flow channel around the lower part of the keyhole. This results in a contamination of the weld pool due almost entirely to the top coating and restricted to the upper portion of the FZ [48]. However, the mechanical properties of these kinds of weld in butt joint configuration and hot-stamped conditions, i.e., those of a final TWB press-hardened part, should be better investigated.…”