From defect inheritance to high-performance Joints: Laser deep-penetration welding of SLM-fabricated 316L/CuSn10 composites

Intrinsic defects and immiscibility-driven segregation fundamentally limit the joining reliability of additively manufactured dissimilar-metal composites. Here, deep-penetration laser welding is used to join selective laser melting-fabricated 316L/CuSn10/316L laminated structures, aiming to elucidate how melt-pool dynamics govern defect elimination and mechanical performance. The results show that sufficiently high and stable heat input establishes a highly convective molten pool dominated by Marangoni flow, which actively annihilates native volumetric defects and heals interfacial cracks, increasing the relative density from ∼98% in the as-built state to 99.86%. Concurrently, the coupled action of recoil pressure and surface-tension gradients induces macroscopic liquid–liquid phase separation, driving Cu-rich liquid toward the weld periphery. The resulting phase redistribution and spheroidization of the Cu-rich phase suppress deleterious grain-boundary wetting and liquation cracking. An asymmetric interfacial response is established, characterized by epitaxial growth on the 316L side and grain refinement on the CuSn10 side, while a coherent or semi-coherent γ-Fe/α-Cu interface with a specific [−110] orientation relationship ensures robust metallurgical bonding. Consequently, the joint exhibits a superior strength–ductility synergy, achieving a tensile strength of 656.7 MPa with an elongation exceeding 25%, governed by a stress accommodation, load transfer-dominated failure mechanism. This work establishes a unified mechanistic framework linking defect inheritance, melt-pool-driven healing, phase separation, and mechanical response, providing general guidance for joining AM dissimilar-material systems.