Defectometry, distortion analysis and metallurgical properties in the keyhole and conduction mode of laser beam welding of Al–Mg–Sc alloy butt joints

Abstract

A study on porosity evolution, distortion evolution and metallurgical properties of laser beam welded AA 5024 (Al–Mg–Sc) alloy have been presented here. A comparative assessment was done for two welding types, i.e. deep penetration (keyhole) and partial penetration (conduction) welding were used for joining AA 5024 sheets. Detailed Finite element-based thermo-mechanical simulations have been carried out to simulate the temperature profiles and their temporal evolution of distortion and welding-induced stress for different keyhole and conduction heat sources. Extensive X-ray micro tomography investigation has been done to understand the physics behind the porosity formation. Bands of porosities have been observed in conduction welding at the edge of the weld pool. The inherent residual stress evolution was also mapped, and the reason behind the propensity to failure was investigated. High-cycle fatigue tests were done to check the endurance of these welded joints. The low power and high speed for keyhole welding and low power and low speed for conduction welding have been seen to give rise to minimal distortion. The conduction welded specimens at low speed, i.e. 0.5–1 m/min, and high power 3.5–4 kW region performed better under HCF.