Effects of polymer sealant interlayer on quality of EN AW-2024-T3 aluminum alloy lap joint prepared by friction stir welding

Abstract This study investigates the influence of polymer interlayers on the mechanical properties and fracture behavior of friction stir welded EN AW-2024-T3 aluminum alloy joints. Aqualock AL 6002 (Adhesive_1) and 3M Adhesion Promoter 86A (Adhesive_2) were selected as polymeric sealants for EN AW-2024-T3 aluminum alloy interfaces. Force analysis revealed that the choice of polymer interlayer significantly affects the axial force during welding, with Adhesive_1 joints showing a significant reduction in force compared to other variants. The axial force during FSW in Adhesive_1 was 18% less than in Adhesive_2. Cross-sectional analysis revealed distinct features in joint morphology and defects, with Adhesive_1 joints exhibiting favorable thermal stability and minimal defects compared to Adhesive_2 joints. Tensile strength analysis showed a significant increase in load capacity for the Adhesive_1 (9470N) joint, while the Adhesive_2 (5030N) joint exhibited reduced strength due to inadequate heat flow. The Adhesive_1 joint showed a 93% increase in tensile strength compared to Adhesive_2. The mixing of Adhesive_2 with the joint area produced hard complex particles that reduced the strength of the final joint. Fracture analysis revealed complex fracture mechanisms, with Adhesive_1 joints exhibiting ductile fracture zones and Adhesive_2 joints exhibiting quasi-cleavable intergranular cracking. Microhardness distribution analysis showed variation between the joint variants, with Adhesive_2 joints showing higher microhardness in the weld nugget.