Surface roughness engineering of mechanical interlocking for enhanced metal–polymer adhesion in additive manufacturing

Laser Powder Bed Fusion (PBF-LB/M) is an emerging technology that enables excellent dimensional accuracy and mechanical performance. In this work, we present a systematic approach to investigate roughness engineering for metal–polymer bonding. By carefully tuning the process, the averaged surface roughness (Ra) of the printed part was precisely modulated while maintaining the relative density (> 99%). The resultant surfaces, ranging from a polished surface (Ra = 2.1 µm) to as-built morphologies with small (26.7 µm), large (56.9 µm), and severe roughness (65.9 µm), were investigated for metal–polymer bonding. Lap-shear tests with representative silicone polymers (EcoFlex, Dragon Skin, and PDMS) revealed that this engineered roughness achieved superior adhesion strength between metal and polymer. Specifically, the large roughness engineered condition (Ra = 56.9 µm) yielded adhesive strengths of 220.8, 321.0, and 717.2 kPa for EcoFlex, Dragon Skin, and PDMS, respectively. Compared to non-treated polished surfaces, this strategy led to a substantial increase in adhesive strength by 214.3% (EcoFlex), 228.5% (Dragon Skin), and 228.7% (PDMS). Finally, the multi-roughness regions were fabricated within a single part, potentially offering the site-specific functional service requirements. This approach establishes a straightforward manufacturing-integrated strategy to achieve high-performance metal–polymer joints, enabling design-flexible multi-material architectures for functional hybrid systems.