Porosity reduction in Nd–YAG laser welding of stainless steel and inconel alloy by using a pulsed wave

Abstract

This study investigates the influence of the Nd–YAG laser power wave mode on the porosity and mechanical properties of SUS 304L and inconel 690 weldments. Initially, a rectangular laser power waveform is specified. The output is then progressively changed from a pulsed wave mode to a continuous wave mode by reducing the value of ΔP (ΔP = Pp−Pb, where Pp is the peak power and Pb is the base power) to zero. Bead-on-plate (BOP) and butt welding are performed at a constant mean output power (1.7 kW). The BOP results demonstrate that the depth/width (D/W) ratio of both materials increases with ΔP and attains a maximum value when full penetration just occurs. The D/W ratio and the travel speed for full penetration are higher for SUS 304L than for inconel 690. In butt-welds of inconel 690 and SUS 304L, the porosity ratio decreases from 7.1% to 0.5% and from 2.1% to 0.5%, respectively, as ΔP increases from 0 to 2780 W. Therefore, the tensile strength and percentage elongation are enhanced significantly in inconel 690. The degree of porosity reduction in inconel 690 exceeds that of SUS 304L. This suggests that the viscosity of the molten inconel 690 metal is higher than that of SUS 304L. Consequently, the effect of porosity reduction due to the increase in molten metal fluidity caused by increasing ΔP is greater for inconel 690 than for SUS 304L.

Effects of Different Shielding Gases and Power Waveforms on Penetration Characteristics and Porosity Formation in Laser Welding of Inconel 690 Alloy

“…Furthermore, for welds with low porosity, the increased pulse effect at higher levels of ÁP yields only a marginal reduction in porosity. 21) Therefore, the P r reduction with increasing ÁP in the specimens welded under He shielding is less than that observed under Ar. Meanwhile, under N 2 shielding, increasing ÁP has no discernible effect in reducing the specimen porosity.…”

“…Therefore, it appears that the enhanced ability of the bubbles to escape from the weld pool under a high ÁP more than compensates for the higher tendency of bubbles to become entrapped. Previous studies 21,38,45,46) of the relationship between ÁP and porosity formation in metals of different viscosities welded using a Nd-YAG laser revealed that as ÁP increases, the P r of aluminum alloys increases, 45,46) while that of stainless steel decreases slightly 38) and that of Inconel 690 decreases more significantly. 21) Therefore, it is apparent that the reduction in P r associated with increasing ÁP for high-viscosity materials is more significant than that for low-viscosity materials (viscosity: Inconel 690 > stainless steel > aluminum alloys).…”

“…14,30,31) The content of the trapped bubbles depends on the nature of the shielding gas (e.g. the type of shielding gas), 14,18) the shielding conditions, 16,[32][33][34] the vapour pressure of the metal, 35,36) the viscosity of the molten metal 21) and the dynamics of the keyhole during the welding process. 10,37) The floatability of the bubbles is affected by the characteristics of the output power (e.g.…”

Effects of Shielding Gas Flow Rate and Power Waveform on Nd:YAG Laser Welding of A5754-O Aluminum Alloy

“…9. This behavior is very different from that observed in the laser welding of Inconel and stainless steel 27,28) and is thought to arise as a result of a number of different factors, including the poorer weldability of A5754 aluminum alloy compared to steel materials, and a higher thermal conductivity of aluminum alloy than that of steel. Figure 9 shows that the weld bead geometry depends on the value of ÁF.…”

“…Hence, the penetration depth in the PW mode is greater than that in the CW mode. [27][28][29] As ÁP is increased, i.e. P p increases and P b decreases, the energy absorption becomes more remarkable.…”