Fatigue strength of aluminum butt joints by different welding techniques and local approaches

Achieving high fatigue strength in as-welded butt joints requires minimizing geometrical imperfections and local defects while ensuring full penetration and a smooth transition between the base material and weld reinforcement. Different welding techniques exhibit varying capabilities to meet these requirements. The objective of the present study is to compare the fatigue strength of butt-welded joints produced using solid-state and fusion welding processes – specifically friction stir-, laser-, gas tungsten arc-, and gas metal arc welding. Fatigue tests and detailed weld geometry characterization were performed on 4 mm thick plates of aluminum alloys 5083-H111, 5754-H111, 5754-H22, and 6082-T6. Additional tests on 8 mm thick specimens were conducted to evaluate potential thickness effect. Optical profilometer data were used to create two-dimensional finite element models, enabling the determination of fatigue notch factors using the effective notch stress concept and the theory of critical distances. The experimental fatigue tests showed that FSW butt joints exhibited the highest fatigue strength, while lower fatigue strength was observed in fusion-welded joints, primarily due to higher fatigue notch factors and welding-induced angular distortions. The effective notch stress approach, applied with reference radii of 0.05 mm, 0.3 mm, and 1 mm, provided conservative estimates of fatigue strength across all joint types No significant differences were found in the fatigue strength of similar butt joints made from the different aluminum grades studied in this work. The results highlight that geometrical factors, including misalignment and notch geometry, are the primary parameters governing the fatigue strength of welded aluminum butt joints.