Additive manufacturing, especially laser powder bed fusion (L-PBF), enables complex metal structures and even multi-material components. However, using different metal powders in one build often leads to contamination, hardware limitations, and interfacial defects such as brittle intermetallics, cracks, and voids. These challenges restrict the feasibility of multi-material metal printing. To overcome these limitations, this study introduces a hybrid manufacturing method that integrates L-PBF with laser welding and incorporates metallic foils as secondary materials. Using foils rather than powders provides several advantages: reduced contamination risk, improved powder recovery, and altered thermal and mixing behavior at the interface. Because foils change heat flow and melt dynamics, they can suppress the formation of brittle phases and minimize interfacial defects. The effectiveness of this foil-assisted strategy was investigated through three representative material systems: Steelâ Copper (relevant for heat exchangers), Aluminumâ Titanium (common in lightweight aerospace structures), and Titaniumâ Copper (a less explored but promising combination). For each pair, conventional powderâ powder samples were first fabricated as benchmarks, followed by powderâ foil samples. In situ synchrotron measurements, ex situ microstructural analysis, and complementary FEM, CFD, and CALPHAD simulations were used to examine solidification behavior and material interactions. In the Steelâ Copper system, substituting copper powder with foil led to the formation of an Fe-rich BCC phase with spherical morphology, arising from the Feâ Cu miscibility gap. Contrary to earlier reports of cracking caused by mismatched thermal properties, the current study showed a strong, defect-free interface between copper and 316L steel. These encouraging results prompted additional experiments to investigate the role of the BCC phase in interface strengthening and overall solidification behavior. The Aluminumâ Titanium system represents one of the most difficult material combinations due to extensive intermetallic formation and large differences in thermophysical properties. Conventional powderâ powder samples displayed severe interfacial cracking and delamination. In contrast, replacing titanium powder with Ti-6Al-4V foil significantly modified the interfacial thermal field and mixing pattern, resulting in a more robust interface and substantially fewer defects. For the Titaniumâ Copper system, powderâ powder processing produced fine FCC copper-rich dendrites but also inter-dendritic cracking and voids. Foil-assisted fabrication, however, yielded a semi-amorphous interfacial region consistent with the thermodynamics of the Cuâ Ti system, indicating a more favorable solidification path and improved structural integrity. Overall, the results demonstrate that integrating metallic foils into multi-material additive manufacturing improves interfacial quality across systems prone to brittle intermetallics or thermal mismatch. Foils reshape heat transfer and mixing, promoting the formation of novel phases and enhancing interface stability. While the current approach is limited to relatively simple geometries and largely horizontal interfaces, it represents a promising direction for advancing multi-material metal printing and expanding its design possibilities.