Planetary laser welding of medium-thickness aluminum alloys: microstructure, texture, and performance enhancement

Degradation of post-weld mechanical properties in medium-thickness aluminum alloys limits their broader application. In this study, a planetary laser welding (PLW) system was employed to butt-weld 2024 aluminum plates, combining a high-speed planetary beam with a oscillating satellite beam. With a single laser, welds exhibit an I-shape profile (2.1 mm width) with pronounced internal cracks and porosity. In contrast, PLW expands the upper molten pool region and enhances melt circulation, effectively reducing crack formation. Increasing the oscillation amplitude from 0.5 to 1.5 mm, progressively separated the planetary and satellite keyholes, concentrating energy at the base (0.5 mm), enlarging and stabilizing the keyhole opening (1.0 mm), and ultimately inducing instability and collapse at full separation (1.5 mm). Higher oscillation frequencies disrupt the temperature gradient, accelerate the columnar-to-equiaxed transformation, refine grain size, disperses texture, and increase grain boundary density. However, at 500 Hz, oscillations drive oxygen ingress and form oxygen-rich precipitates that act as crack-initiation sites. Optimally, at 1.0 mm amplitude and 200 Hz frequency, tensile strength reached 376 MPa and elongation was 3.18 %. These results demonstrate that PLW precisely controls molten pool dynamics and microstructural evolution, producing high-performance welds in medium-thickness aluminum alloys.