Surface Microstructure Regulation via Femtosecond Laser for Enhancing Laser Welding Strength of PVC/PA66: Mechanisms and Optimal Parameters

The laser welding of incompatible polymers, such as polyvinyl chloride (PVC) and polyamide 66 (PA66), is often constrained by weak interfacial bonding, making it challenging to achieve joint strength that meets engineering requirements. This study proposes a welding reinforcement strategy based on femtosecond laser surface microstructuring regulation. First, high-precision and controllable microgroove structures were fabricated on the PVC surface, and the joint welding strength was significantly enhanced via the macroscopic mechanical interlocking effect. The influence of groove width, depth, spacing, and configuration on welding performance was systematically investigated. Subsequently, combined with fracture morphology characterization and finite element simulation, the interfacial reinforcement mechanism and stress regulation law of the microgroove structures were revealed. The results indicate that under the optimal process parameters (groove width = 70 μm, depth = 70 μm, spacing = 130 μm, welding power = 13 W), the joint with vertical groove structures achieves a maximum shear strength of 15.4 MPa, which is significantly superior to that of untreated joints. Additionally, vertical groove structures yield optimal unidirectional load-bearing strength, while grid groove structures effectively mitigate stress concentration under multidirectional loading, exhibiting better adaptability to complex stress conditions. This work provides a high-precision and versatile process for welding highly incompatible polymer systems, and also offers an important theoretical reference for process optimization and engineering applications of laser transmission welding of dissimilar polymers.