Effects of welding parameters on the microstructure and mechanical properties of the AA6061 aluminium alloy joined by a Yb: YAG laser beam

Abstract

In this study, the effects of Yb: YAG laser welding parameters on the microstructure and mechanical properties of AA6061-T4 joints were analysed. Samples without any welding defects such as porosity, melt pool collapse, and hot cracking were produced with different welding parameters. Energetic processing parameters had a significant influence on the fusion zone (FZ) and heat-affected zone (HAZ) microstructure and dimensions, in addition to local and global mechanical properties. The weld bead width increased with increasing power and energy densities and reduced the weld bead tensile properties. High welding travel speed produced a more elongated weld pool and ripples resulted in a ‘V’ shape. A significant quantity of axial heterogeneous nucleation was observed in the FZ centre of these weld beads because of the low-energy density. In contrast, low welding travel speed produced C-shaped ripples and a few axial grain nucleation sites in the FZ. The latter was evidence of a slower solidification rate. Dendrite secondary arm spacing measurements confirmed this hypothesis. It was observed that axial grains in the FZ centre improve the weld bead tensile properties. Compared to the base material (BM), the hardness in the FZ was reduced and identical in the HAZ. The FZ hardness depended on the welding parameters. Digital image correlation (DIC) strain measurements indicated higher deformation near the FZ, but when geometrical defects were removed, the FZ deformed more homogeneously.