Investigation of the effects of femtosecond laser metal surface texturing on bonding of PA6 to steel

This paper investigates the effects of femtosecond laser surface texturing on the interfacial bond strength of steel and a thermoplastic polymer PA6 film. Ultimately the textures will be used for hybrids that are manufactured using a near-infrared (NIR) laser-assisted automated tape placement (ATP) process and carbon fibre / PA6 composites, therefore the NIR absorptance of the textured metal substrate is also of interest. To identify the influence of different surface structures on the bonding strength, lap shear samples were manufactured with laser textures varying in pulse length, hatch distance and ablated depth and tested by ASTM D 3165. The surface structures were analysed with white light interferometry (WLI) and scanning electron microscopy (SEM). Additional optical measurements in the infrared radiation range of 900 nm to 1100 nm were executed with a spectrophotometer to evaluate the laser absorptance for the NIR automated tape placement process. The lap shear strength increased to the highest value of 31.9 MPa with a tooth shaped laser texture using a 275 fs laser pulse width, a hatch distance of 600 μm an ablated depth of 40 μm. Also the absorptance for this sample increased by approximately 13% to 73% compared to the unprocessed pickled steel.