Direct Joining of Recycled Polypropylene Composites with Aluminum via Screw Extrusion-Based Additive Manufacturing Toward Three-Dimensional Polymer–Metal Hybrids

This study investigates the influence of nanosecond laser ablation micropatterns on aluminum surfaces for direct joining strength in polymer-metal hybrids fabricated using extrusion-based additive manufacturing of recycled polypropylene (rPP) composites. While integration of polymer extrusion-based processes with direct joining represents a highly efficient production approach, achieving both joining strength comparable to conventional methods and dimensional stability remains challenging. Contrary to reported poor joining characteristics of virgin polypropylene, rPP demonstrated effective joining when aluminum surfaces were heated above the crystallization temperature. Glass fiber-reinforced rPP exhibited minimized shrinkage and warping, enabling continuous building processes following initial joining.Single lap shear testing across two materials and three laser micropattern configurations on Al6061 substrates revealed that micro-groove patterns parallel to nozzle path direction provide optimal joining performance. Statistical analysis confirmed significant effects of both material type and surface patterns on failure loads. Maximum failure loads of 2080 N were achieved over 10×13.2 mm² joining areas, enabling fabrication of box-shaped polymer-metal hybrids with minimal warping. This integrated manufacturing approach offers efficient application potential for lightweight multi-material component fabrication based on recycled materials and environmentally sustainable processes.