Torch Oscillation-Induced Microstructure Evolution, Deformation Mitigation and Mechanical Property Enhancement in Thin-Plate 5083 Aluminum Alloy Butt Welds

AA5083 Al-Mg alloy is widely applied in lightweight marine and transportation structures, yet thin-plate arc welding suffers from prominent out-of-plane deformation and coarse columnar-grain issues originating from concentrated arc heat input. This work adopted sinusoidal torch-oscillation-assisted CMT to conduct butt-welding experiments on 2 mm-thick AA5083-H112 sheets with ER5183 filler wire. Five oscillation amplitudes ranging from 0 mm to 4 mm were set to explore the coupled effects of oscillation amplitude on weld geometric features, three-dimensional base-plate deformation, weld-zone microstructural evolution, crystallographic texture and tensile-fracture behaviors. The results reveal that appropriate torch oscillation redistributes arc heat flux and introduces molten-pool stirring. It mitigates thin-plate out-of-plane deformation, refines grains, and promotes equiaxed-grain formation with a slight decrease in the measured texture intensity. The joint's comprehensive mechanical performance is highest at an oscillation amplitude of 2 mm among the tested conditions in this work: ultimate tensile strength, yield strength, and elongation attain 219.03 MPa, 112.14 MPa, and 18.45%, accompanied by typical ductile-dimple fracture features. Nevertheless, amplitudes exceeding 3 mm destabilize the molten pool and trigger pores and local lack-of-fusion defects, leading to sharp performance deterioration and brittle fracture. The competitive relationship among deformation relief, grain refinement, and defect generation determines the valid amplitude window. This study provides an experimental reference for high-quality CMT welding of thin-gauge 5083 aluminum alloy via torch-oscillation process regulation.