Influence of Temperature Profile during Laser Welding of Aluminum Alloy 6061 T6 on Microstructure and Mechanical Properties

In the present study, laser welding was carried out with CO2 laser on a 2mm thick aluminum alloy (6061-T6) sheet to study laser weldability of this heat-treatable aluminum alloy. Screening experiments were performed initially to enumerate the power density requirement for proper coupling of the laser with the material. Bead on plate experiments were conducted to recognize situation under which stable keyhole and welds with minimum defects (porosity and cracks) can be produced. Recognized process window (3kW power, 4m/min welding speed, and 18L/min Helium flow rate) obtained from initial trial was used in butt welding experiment and the resulted weld was characterized by macroscopic and microscopic observation, microhardness study, and tensile test. The microstructure reveals porosity and crack-free welds and hardness data confirmed presence of heat-affected zone (HAZ) and huge drop in overall hardness after welding. After post-weld treatment (aging treatment), the hardness was increased marginally, but base hardness could not be achieved. Thermal profile experienced by the material during welding was calculated and it revealed that the mechanical properties of the material decreased due to temperature experienced by the material lead to loss of aging properties of the material.