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

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 (delta) P ((delta) P=Pp-Pb, where Pp is the peak power and Pb 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 (delta) F ((delta) F=Ff-Fb, where Ff is the face shielding gas flow rate and Fb is the back shielding gas flow rate). The BOP welding results show that reducing the value of (delta) P 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 (delta) F ((delta) FH) specimens are approximately three times higher than those of the low (delta) F ((delta) FL) specimens. This is primarily due to the absence of hot cracking in the (delta) FH specimens, together with a finer microstructure and a lower level of porosity. This study demonstrates that the effect of (delta) F on the weld bead geometry, microstructure, hot crack susceptibility and mechanical properties is far higher than that of (delta) P. However, the effect of (delta) P on the change of welding speed is higher than that of (delta) F.