Graphene nanoplatelet reinforcement of dissimilar AA6082-T6/AA2050-T8 friction stir welded joints: Mechanical, tribological, and dynamic mechanical performance

: Dissimilar friction stir welding (FSW) of precipitation-hardened aluminum alloys remains challenging due to weld-zone softening, heterogeneous material flow, and microstructural instability, which often limit joint strength and service performance. This study presents a graphene nanoplatelet (GNP)-reinforced dissimilar AA6082-T6/AA2050-T8 FSW joint and provides a comprehensive assessment of its mechanical, tribological, and dynamic mechanical behavior. The novelty of the work lies in the integrated investigation of graphene-assisted strengthening in dissimilar Al–Mg–Si/Al–Cu–Li welds, combining tensile performance, hardness distribution, wear resistance, friction behavior, and dynamic mechanical analysis within a single framework. Similar joints (AA6082-T6/AA6082-T6 and AA2050-T8/AA2050-T8), an unreinforced dissimilar joint, and a graphene-reinforced dissimilar joint containing 0.5 wt.% GNPs were fabricated under identical FSW conditions. Mechanical characterization, microhardness mapping, pin-on-disc tribological testing, dynamic mechanical analysis (DMA), and SEM/EDS examinations were performed to evaluate the influence of graphene reinforcement on weld performance. The graphene-reinforced dissimilar joint exhibited substantial improvements, achieving a yield strength of approximately 398 MPa, an ultimate tensile strength of 525 ± 12 MPa, and a joint efficiency of approximately 107% relative to AA2050-T8. Furthermore, the reinforced weld attained an average hardness of 153 ± 4 HV, a reduced specific wear rate of 4.83 × 10 -4 mm 3 /N·m, and a lower coefficient of friction of about 0.29. Dynamic mechanical analysis revealed superior stiffness retention, higher dynamic viscosity, improved damping stability, and a reduced stiffness-loss rate as temperature increased. SEM observations confirmed a refined weld-zone microstructure, uniform reinforcement distribution, and predominantly ductile fracture characteristics. The results demonstrate that graphene nanoplatelets effectively mitigate FSW-induced softening, improve load-transfer capability, enhance tribological stability, and increase thermo-mechanical performance. These findings establish graphene reinforcement as an effective strategy for developing high-performance dissimilar aluminum FSW joints for lightweight aerospace, transportation, and advanced structural applications.