Effect of triangular spew fillet angle on the strength and water aging behavior of 6061 aluminum alloy adhesive joints

The geometry of spew fillets strongly influences the stress distribution of adhesively bonded joints. Optimizing the fillet shape to achieve a smooth transition between adherends reduces stress concentration at the overlap ends and enhances joint strength. However, systematic studies on the interaction between precisely controlled fillet geometry and long-term aging environments remain limited, largely due to the difficulty of controlling fillet shapes using conventional manufacturing methods. In this study, a 3D-printing-assisted method was employed to fabricate 6061 aluminum single-lap joints with controlled triangular spew fillet angles ranging from 15° to 90°. The effects of fillet angle on tensile and bending performance were systematically investigated, and long-term immersion aging was conducted in distilled, tap, and saltwater environments. The results show that introducing spew fillets significantly improves joint strength, with the optimal performance achieved at a fillet angle of 15°. Compared with joints without fillets, the tensile and bending strengths increased by 39.19% and 20.24%, respectively. Although joint strength decreased with aging time in all water environments, the strengthening effect of the fillet remained significant, and the joints with a 15° fillet consistently exhibited the highest strength. Fracture analysis further confirmed that optimized fillet geometry effectively redistributes stresses and enhances load-carrying capacity.