Effects of adjustable ring mode laser-beam control on microstructure and mechanical properties of AA6N01-T5 aluminum alloy in laser-arc hybrid welding

This study evaluated the effects of beam control in adjustable ring mode laser-arc hybrid welding on the microstructure, porosity, and mechanical properties of a 5-mm-thick AA6N01-T5 Al alloy. Three laser-beam conditions—ring-beam hybrid welding (RBHW), center-beam hybrid welding (CBHW), and dual-beam hybrid welding (DBHW)—were compared under similar heat input conditions. The factors with the most significant influence on the mechanical properties in the welding of the AA6N01-T5 Al alloy are the porosity, grain size, and presence of strengthening precipitates. The weld porosity was quantified via high-resolution X-ray three-dimensional computed tomography, the grain structure was characterized via electron backscatter diffraction, the distribution and content of Mg—a key element in precipitation strengthening—were examined via electron probe microanalysis, and tensile and microhardness tests were performed in compliance with ASTM standards . RBHW achieved the lowest porosity (0.77%) and the highest elongation (8.7%) owing to the stable keyhole geometry and enhanced molten-pool convection. DBHW exhibited the smallest equiaxed grain size (179.43 μm) and the lowest Mg loss (0.89 wt%), resulting in the highest tensile (178.9 MPa) and yield (121.8 MPa) strengths. CBHW exhibited a combination of high porosity, coarse grains, and severe Mg loss, which degraded the mechanical performance of the weld. These findings clarify that the laser-beam energy distribution influences the molten-pool behavior, microstructure, and mechanical properties of the weld, thereby affecting the performance and reliability of high-strength Al alloy welds in lightweight manufacturing applications.