In this study, bimetallic structures composed of pure copper and stainless steel 630 (STS 630) were fabricated using powder bed fusion (PBF) to evaluate deposition quality, solidification cracking mechanisms, and mechanical properties. Optimal processing conditions were determined by analyzing mixed zone depth and interfacial characteristics under various parameters. Stable deposition without defects was achieved at low energy densities (≤0.15 J/mm). Intermediate energy densities (0.17–0.44 J/mm) resulted in deposition cracks without edge cracking, while high energy densities (≥0.5 J/mm) caused deposition cracks and edge cracks due to residual stress. Rapid cooling within the Fe–Cu mixed zone promoted liquid-phase separation into Fe-rich and Cu-rich phases via binodal and spinodal decomposition mechanisms. Deposition cracks were observed in compositions with 13–34 wt% Cu, driven by δ-Fe to γ-Fe transformation, solidification temperature ranges, and insufficient residual liquid. However, compositions with sufficient residual liquid mitigated crack susceptibility through an effective back-fill effect. Nanoindentation tests revealed gradually decreasing hardness distributions with increasing mixed zone depth; however, localized phase separation and cracking led to significant local hardness variations. Tensile tests indicated that fractures predominantly occurred in the pure copper region, whereas specimens with excessively deep mixed zones fractured prematurely at the interface or within the mixed zone. Furthermore, extensive phase separation and cracking markedly reduced elongation. This study underscores the critical importance of optimizing processing parameters, controlling liquid-phase separation and cracking, and carefully managing mixed zone depth to enhance the mechanical performance of bimetallic structures.