<p>This study investigates numerically the effects of a bimetallic flexible fin on the heat transfer and melting process of liquid phase change material (PCM) within a cavity. The bimetallic fin is attached to the left heated wall of the cavity. The governing equations of the system model in the fluid and structure domains are written in the Arbitrary Lagrangian–Eulerian (ALE) formulation and then solved by the Multiphysics commercial software (COMSOL 6.1). The results demonstrate that the bimetallic flexible fin significantly enhances heat transfer compared to a fixed fin, leading to faster melting of the PCM for different values of Rayleigh number (Ra). It was also found that at the onset of the heating process, the enhancement in heat transfer rate due to the use of a flexible fin is approximately 180% in convective heat transfer at Ra = 10³ and 35% at Ra = 10⁵. Additionally, the maximum average Nusselt number in the flexible fin case reaches 2 × 10⁴ at the dimensionless time, τ = 0.01, whereas in the case of a fixed fin, the maximum value of the Nusselt number is 30 at the onset of the heating process. Moreover, the bimetallic fin configuration leads to a more uniform temperature distribution and faster melting time (up to 11% reduction) compared to the fixed fin. This work pioneers the use of passive bimetallic actuation to amplify natural convection, contrasting with static fins, nanoparticle additives, or rigid metal foams in prior studies.</p>