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

Abstract

Although the microstructure, hot crack susceptibility and porosity of aluminum alloy laser welds are affected by many welding parameters, the effects of the shielding gas flow rate and the power waveform are particularly significant. In this study, a high-power Nd:YAG laser is used to weld A5754-O aluminum alloy sheets of 1 mm in thickness. Initially, bead-on-plate (BOP) welding is performed using a rectangular waveform with a constant mean output power and three different levels of ÁP (ÁP ¼ P p À P b , where P p is the peak power and P b is the base power). Butt welding is then performed using the appropriate BOP welding speed, which is lower than the welding speed for just full penetration, and one of two levels of ÁF (ÁF ¼ F f À F b , where F f is the face shielding gas flow rate and F b is the back shielding gas flow rate). The BOP welding results show that reducing the value of ÁP increases the welding speed required for full-penetration, and therefore increases the penetration depth to bead width ratio and the micro-hardness of the weld bead. The butt welding results show that the tensile strength and total elongation properties of the high ÁF (ÁF H ) specimens are approximately three times higher than those of the low ÁF (ÁF L ) specimens. This is primarily due to the absence of hot cracking in the ÁF H specimens, together with a finer microstructure and a lower level of porosity. This study demonstrates that the effect of ÁF on the weld bead geometry, microstructure, hot crack susceptibility and mechanical properties is far higher than that of ÁP. However, the effect of ÁP on the change of welding speed is higher than that of ÁF.

The Effect of Process Parameters on the Microstructure and Mechanical Properties of AW5083 Aluminum Laser Weld Joints

“…Sagging was detected in the weld joint created without the use of a shielding atmosphere (Figure 3e). Kuo et al observed that a weld with a concave shape is a result of a larger gas pressure in the downward direction [14]. In this case, no protective gas was utilized.…”

“…The weld bead had a concave character when 5 L/min gas flow rate was used. On the other hand, weld concavity was found at the flow rate lower than 20 L/min [14]. Katayama et al found that defocusing of the laser beam by plasma above the metal surface produces shallow weld beads.…”

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

“…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).…”

Influence of shielding gases on porosity during laser welding of AZ31B magnesium alloy

“…Elements with a low melting point, in our case Mg, evaporate during laser welding and are trapped in the WM, promoting porosity formation [44]. According to Kuo et al [45], Al 2 O 3 is hygroscopic and absorbs ambient moisture. Toda et al [46] found that the mechanical properties of aluminium alloys are sensitive to the presence of micropores.…”