Impact of graphene addition on intermetallic compounds (IMC) and mechanical properties of Sn–Bi solder alloys under thermal cycling

• Graphene nanosheets enable concurrent microstructural refinement and interfacial stabilization in low-melting Sn–Bi solders under severe thermal cycling. • An optimal GNS content (0.05 wt%) suppresses intermetallic compound growth by > 40% after reflow and 34% after 1000 thermal cycles, revealing an effective long-term diffusion barrier mechanism. • β-Sn dendrite refinement of ∼ 8% (reflow) and ∼ 9.7% (thermal cycling) demonstrates graphene-assisted heterogeneous nucleation and microstructural stabilization. • Elastic modulus enhancement up to > 50% after thermal cycling confirms sustained load transfer efficiency and mechanical robustness of graphene-reinforced solder joints. The addition of graphene nanosheets (GNSs) to Sn–Bi alloys has been explored to increase the performance and reliability of solder joints under severe thermal conditions. In this study, Sn-Bi–xGNSs alloys ranging from 0.0 to 0.5% by weight were prepared and applied to copper substrates, subjected to remelting and thermal cycling. The microstructures and intermetallic compounds (IMCs) were evaluated by optical microscopy and microsection, and the mechanical properties by nanoindentation. All alloys composed of GNSs in the microstructure after remelting had refinement of the primary β-Sn phase in relation to the pure alloy of 0.0%, while after thermal cycling with 0.05% had the best refinement condition of the β-Sn phase, while contents > 0.3% resulted in agglomeration of GNSs and loss of efficiency. After remelting and thermal cycling, the sample with 0.05% by weight showed a reduction of more than 40% and 34% in the thickness of the IMC layer, respectively. In the post-remelting sample with 0.1%, there was a 16% increase in the modulus of elasticity and, after thermal cycling, a 50% increase in the modulus of elasticity. The research highlights the influence of GNSs on microstructural refinement, control of IMC growth, and mechanical stability under thermal cycling.