Low Speed Laser Beam Welding (LBW) of 6061-T6 Alloys Using a 300 W Pulsed Nd:YAG Laser: Microstructure Development and Crack Formation
B. Ghosh, S. Mondal, S. Chandra, J.D. Majumdar and M. Ghosh
The feasibility of applying a pulsed 300 W Nd:YAG average power laser for autogenous laser beam welding (LBW) of 6061-T6 alloy was studied under the variation of laser current and weld speed from the perspective of weld microstructure, micro-segregation, cracking susceptibility and consequential mechanical characteristics. The results displayed that with proper control of different parameters, the full penetration can be achieved but the formation of typical welding defects, such as crack formation and oxide inclusion could not be prevented. Solidification cracking may be taken place in the fusion zone (FZ) during the solidification, while liquation cracking may preferably be taken place in the partially melted zone (PMZ). This study focuses on these two kinds of cracking and it was observed that significant solute segregation, oxide inclusion and welding associated thermal strain were the governing factors for crack initiation and propagation. While the hardness loss of AA6061-T6 alloy welds was severely affected by both the facts of microsegregation and dissolution of strengthening precipitates. The acquired results provide support for technology optimization of average power Nd:YAG LBW.
Keywords: Nd:YAG laser, AA6061-T6, aluminium alloy, laser beam welding (LBW), microhardness mapping, welding metallurgy, microstructure, weld cracking