Laser-assisted fabrication of AISI 1018 steel–PET–steel sandwich composites with surface-engineered interfaces: Mechanical and chemical insights

Metal–polymer–metal (MPM) sandwich composites are increasingly used in lightweight multi-material systems, yet conventional fabrication methods like adhesive bonding, roll bonding, and hot-pressing face several limitations, where laser-based fabrication, with its precision and flexibility, provides a promising alternative. This study experimentally evaluates laser fusion bonding for fabricating AISI 1018 steel–PET–AISI 1018 steel sandwich composites and investigates the effect of surface texturing on interfacial bonding performance. Samples with multiple surface conditions, including smooth (untextured), longitudinal line, transverse line, box, and zigzag textures, are subjected to lap-shear testing to quantify bond strength and joint reliability. Cross-sectional and fracture surface morphologies are examined using optical and electron microscopy, while spectroscopic analyses (FTIR, Raman, and XPS) are conducted to assess polymer retention, chemical integrity, and interfacial chemical interactions. Results show that multidirectional textures, particularly box and zigzag patterns, provide the highest bond strength and lowest variability, outperforming unidirectional grooves. Fracture analysis reveals a combination of cohesive and adhesive failure modes, indicating strong polymer deformation and interfacial adhesion. FTIR and Raman analyses confirm the retention of PET at the steel interface without extensive chemical degradation, while XPS confirms interfacial chemical interactions, including C–Fe bonding and oxygen-related modifications. These findings demonstrate that laser-based fusion bonding effectively produces robust interfacial adhesion in MPM composites and has the potential to serve as a scalable alternative to conventional fabrication techniques.