Investigation of thickness-dependent inhomogeneities in 100 mm thick 5083 aluminum alloy butt joints produced by high-voltage scanning electron beam welding

In response to the demanding welding performance requirements of thick 5083 aluminum alloy plates for marine applications, 150 kV high-voltage scanning electron beam welding (SEBW) was employed to join 100 mm-thick 5083 aluminum alloy. The microstructural evolution and mechanical property variations along the joint thickness were systematically investigated. Moreover, the pore distribution characteristics and melt flow behavior were examined, providing insights into the intrinsic correlation between the weld microstructure and its macroscopic mechanical properties. The results revealed that, with increasing thickness, the molten pool solidification rate accelerated, accompanied by an upward trend in pore distribution, with large pores (201–500 μm) appearing in the root region. The weld center exhibited a gradual transition from equiaxed grains to columnar grains toward the fusion boundary, while the grain size within the heat-affected zone (HAZ) decreased progressively with thickness. In both the weld zone (WZ) and fusion zone (FZ), the equiaxed and columnar grains showed a distinct refinement tendency. Precipitates of Mg-rich β (Mg₂Al₃) phase, Mg₂Si phase, and Al_x(Mg, Si, Mn) phases were identified within the weld metal. Owing to variations in local heat input, the joints exhibited non-uniform strain distribution during tensile deformation, with yield strength decreasing as thickness increased. These findings offer valuable insights for optimizing the electron beam welding of thick-section aluminum alloys and improving joint reliability.