The Effect of the Shielding Gas Flow Rate on the Geometry, Porosity, Microstructure and Mechanical Properties of Laser Weld Joints

In this research, studied was the microstructure of AW5083 aluminium alloy butt laser weld joint fabricated under the Ar + 30 vol. % He shielding gas. The light and electron microscopy, computed tomography, microhardness measurements and tensile testing were used for evaluation of the weld joint properties. Porosity volume in the weld metal (WM) was observed by the computed tomography (CT). The volume of porosity in the weld No. 1 was 0.05 mm³, while that in the weld No. 2 was 1.45 mm³. The width of the weld No. 1 was 4.69 mm, the average tensile strength was 309 MPa, and the average microhardness was 55.7 HV0.1. Polyhedral grains with an average grain size diameter of 48 μm were present in the heat-affected zone. The fusion zone (FZ) was of a dendritic structure with an average grain size of 20 μm. Three intermetallic compounds β-Al₃Mg₂, γ-Al₁₂Mg₁₇ and Al₄₉Mg₃₂, which were identified by transmission electron microscope (TEM) analysis, were present in inter-dendritic areas of the WM. The weld joint was characterized by ductile fracture in the base metal (BM). In the FZ, a small number of Al₂O₃ particles of irregular shapes were observed.