Fatigue behavior and interfacial bonding mechanisms of high-aluminum-content PA66 composites and 6061-T6 by friction stir lap welding

Carbon fiber-reinforced polymer (CFRP) composites are increasingly employed in automotive, aerospace, and related industries to achieve lightweight structural designs. Although friction stir lap welding (FSLW) has been widely utilized for metal-thermoplastic composite joining, most existing studies have focused on static strength and fracture behavior, with limited attention to fatigue performance and dynamic damage evolution. In this work, high-aluminum-content particle-filled PA66 composites were manufactured using an electric-field-activated hot-press sintering process and subsequently joined to 6061-T6 via FSLW. The dissimilar joints consistently failed on the composite side under both static and cyclic loading, exhibiting a static tensile strength of 1935 N. As the composite material governed joint failure, fatigue characterization concentrated on the composite side. At 41.7% of the static strength, the composite achieved a fatigue life of 602,999 cycles. These results demonstrate that the proposed dissimilar FSLW joint possesses promising fatigue resistance, supporting its potential application in lightweight transportation structures. The results also provide a basis for future studies aimed at optimizing interfacial design and enhancing the long-term durability of metal-polymer hybrid joints.