Enhancing strength in hybrid aluminum SMC joints through surface laser pretreatment

This study investigates the suitability of laser surface treatment as an adhesion-promoting technique in co-cured hybrid joints between aluminium and Sheet Moulding Compound (SMC) composites with a vinyl ester matrix. Aluminium substrates were treated using laser ablation with varying process parameters to generate different surface morphologies, which were characterized through 3D optical profilometry. The mechanical performances of the resulting joints obtained with laser treated surfaces were then evaluated through shear and tensile tests on single lap and butt joint configurations and compared with grit-blasted reference specimens. The results indicate that laser-treated surfaces significantly improve joint strength, often leading to cohesive failure within the composite. This suggests superior interfacial adhesion compared to the reference treatment. Detailed analysis of fractured surfaces and cross-sections confirmed the critical role of surface morphology. Experimental findings also revealed that, under certain laser treatment conditions, the formation of an oxide layer on the treated surface can negatively impact joint strength. Additionally, the study examined the influence of fibre tow alignment near the bonding surface. It was found that parallel fibre alignment enhances joint strength by minimizing air entrapment at the interface. In conclusion the findings demonstrate that laser ablation is a promising surface preparation method for improving the structural integrity of co-cured metal - composite joints in high-performance applications.