Abstract: To investigate the flow and solidification behavior of non-eutectic corium in rod-bundle subchannels during severe accidents in sodium cooled fast reactors (SFRs), a 19 pin bundle experimental facility with representative triangular subchannels was developed. Comparative experiments were performed in stainless steel and tin rod-bundles to simulate non-melting and melting fuel pin conditions, respectively. A binary NaNO₃-KNO₃ mixture with a wide solid liquid temperature interval was selected as the corium simulant in order to reproduce the phase transition characteristics of multicomponent non-eutectic coriums. Transient temperature distributions were obtained using thermocouple arrays arranged along both axial and radial directions, while flow front evolution and post solidification morphologies were analyzed to clarify the dominant transport and phase change mechanisms. The results show that the corium exhibits a typical three stage thermal evolution during downward propagation, including an initial preheating stage, a rapid temperature rise caused by direct melt contact, and a subsequent temperature decay associated with cooling and solidification. The penetration capability gradually decreases from the inner subchannels to the outer subchannels because of enhanced heat dissipation and premature solidification near peripheral regions. Local blockage induced by solidification forces the subsequent melt to divert into neighboring subchannels, resulting in secondary temperature increase at downstream locations and promoting further axial penetration. The combined effects of flow diversion and energy redistribution are identified as key mechanisms governing sustained melt relocation within rod-bundle geometries. In the stainless steel bundle, rapid interfacial freezing near the inlet produces dense microcrystalline solid layers accompanied by transient temperature oscillations, indicating that the process is mainly controlled by heat transfer driven solidification. In contrast, the tin bundle exhibits lower inlet peak temperatures but longer high temperature residence times because of the high thermal conductivity and low melting temperature of tin. Melting of the rod surface intensifies local blockage and enhances flow nonuniformity between the inner and outer channels. The final solidified structures display rough surfaces, layered adhesion, metallic reaction regions, and bonding between adjacent rods, demonstrating strong coupling among heat transfer, wall melting, and mass transport. Flow front analysis based on the inflection point method further reveals that corium propagation in the tin bundle becomes slower and more heterogeneous because of the coupled melting and solidification interactions. This study presents experimental evidence and mechanistic insights into non-eutectic corium relocation and freezing behavior within complex rod bundle geometries. The findings provide valuable support for severe accident analysis and safety-oriented design optimization of SFR fuel assemblies.