Microstructural evolution and electrochemical corrosion behavior of 2219 aluminum alloy joints fabricated by laser beam oscillation welding

2219 aluminum alloy (AA2219) is widely used in aerospace structures due to its high strength and excellent corrosion resistance. However, welded joints often suffer from reduced corrosion resistance and compromised reliability due to issues such as elemental segregation, coarse-grain structure, and high residual stresses. To enhance the electrochemical corrosion resistance of welded joints, this study introduces the application of laser beam oscillation process control. The electrochemical corrosion behavior of the joints was comprehensively evaluated through a combination of electrochemical measurements (potentiodynamic polarization and EIS) and corrosion morphology observations. The results indicate that the ‘Line’ shaped oscillation significantly governs the microstructural evolution induced by oscillation-facilitated grain refinement during weld solidification, reducing the average grain size from 28.1 μm to 16.7 μm and decreasing the transverse residual stress from 128.6 MPa to 41.5 MPa (a 67% reduction). Electrochemical measurements show that the linear-oscillated joint achieves a polarization resistance (R_f) of 7023 Ω·cm², more than double that of the non-oscillated joint (3379 Ω·cm²), while the Volta potential difference decreases to only 0.053 V compared to 0.110 V for the non-oscillated joint. Morphological observations reveal that the non-oscillated joint suffers from severe continuous intergranular cracking and catastrophic exfoliation, whereas the linear-oscillated joint maintains a smooth and intact surface. These improvements are attributed to the ‘solute trapping’ effect induced by the high-velocity melt flow, which facilitates uniform Cu distribution and thereby reduces the driving force for micro-galvanic corrosion.