Study on the burning loss of magnesium in fiber laser welding of an Al-Mg alloy by optical emission spectroscopy

Abstract

In order to study the burning loss of magnesium, a specially designed device was used to capture the spectrum emitted from the keyhole plasma in deep penetration laser welding of aluminum alloy 5052. The content of magnesium in the weld bead was measured by an electron probe microanalyzer (EPMA). The effect of the welding parameters on the spectral intensity of magnesium plasma was examined, and the distributions of the spectral intensity of magnesium plasma in the radial and depth directions of the keyhole were investigated. Finally, the mechanism of the magnesium loss was analyzed. The results indicate that burning loss of magnesium can be monitored by spectral analysis technique. The welding parameters have a great effect on the burning loss of magnesium. The influence of welding speed on the burning loss of magnesium on the top surface is dependent on the penetration regime. The distribution of magnesium in the weld is not uniform. In the radial direction of the weld bead, the content of magnesium increases from the center to the edge of the keyhole. In the depth direction of the weld bead, the content of magnesium decreases firstly and then increases from the top to bottom. The maximum burning loss of magnesium occurs at the middle of the weld bead.

Effect of alloy element on weld pool dynamics in laser welding of aluminum alloys

“…Zhou et al . (2017) conducted spectroscopic analysis to quantify the composition of metal vapor in laser welding of A5052, and the results indicated that a large amount of Mg was evaporated during the welding process 29 . This research supports our finding that the element with boiling temperature lower than that of aluminum plays a significant role on keyhole formation.…”

“…Researchers have focused on the weld quality in laser welding of various series of aluminum alloys by both experiments and simulations 27 – 29 . These previous researches showed that the aluminum alloy with different compositions had different weldability, which was caused by the differences in weld pool behavior.…”

Microstructures and Mechanical Properties of a Laser-Welded Joint of Ti3Al-Nb Alloy Using Pure Nb Filler Metal

“…From Figure 5a, some gas pores were observed in the weld zone. Unlike that of arc welding, the gas-pore formation of laser welding may be due to the trapping of metal vapor because of the higher power density used for laser welding [26][27][28]. EDS analysis indicated that the weld Al content (8.00 wt %) was reduced compared with the base metal (13.26 wt %), and the Al content (9.62 wt %) of gas pore wall was higher than that of weld, as shown in Figure 5b and Tables 1 and 3.…”

Distribution of Al Element of Ti–6Al–4V Joints by Fiber Laser Welding

“…Laser Welding has been considered as one of the best welding processes for titanium alloys because of its high energy density, fast welding speed, small weld deformation, and flexible operating [1][2][3]. However, in this process, burning loss of some solute elements caused by the high laser intensity (10 6 W/cm 2 ) may reduce joint performance [4,5].…”

“…When the high-energy laser beam focuses on the surface of the base metal, the keyhole is formed within a very short time, and the temperature is even higher than the boiling point of the base metal. Large amounts of vaporization of low-boiling alloy elements occur frequently, and the flow of molten pool would aggravate the burning loss [6] of alloy elements, which will result in the severe inhomogeneity of chemical composition around the weld [4,7]. The inhomogeneity may subsequently cause the microstructure transformation nonuniformity and ultimately affect the mechanical properties of the welded joints [8,9].…”