Mechanism of laser-inducing hierarchical surface structures improving bonding strength of metal-plastic hybrids

The mechanism of laser-inducing hierarchical metal surface structures was investigated both experimentally and numerically, providing insights into improving bonding strength of metal-plastic hybrids (MPHs). For this purpose, metal sheets were first treated with the nanosecond pulsed laser to induce surface microstructures, followed by being put into the mold cavity, and jointed with plastic via the injection molding process. Both aluminum and titanium alloys were adopted as the metals and the glass fiber reinforced polyphenylene sulfide was chosen as the plastic material for MPHs. Specifically, laser parameters including the scanning speed, laser frequency, scan repetition, and modulation switch pulse-width were varied to investigate their impact on metal surface microstructure morphology and thus the MPH bonding strength. It is found that although having no clear trend while changing the laser parameters, the MPH bonding strength is strongly dependent on both surface morphology and material type of the metals. Finally, the process was optimized based on observations concerning the laser-inducing mechanism. The titanium alloy surfaces with bumpy morphology facilitated forming microscale mechanical interlocking between the metal and the plastic, leading to enhanced MPH bonding strength.