Surface topography following pulsed laser texturing: Implications for adhesion and wettability

Abstract

A model for predicting surface topography following nanosecond pulsed laser texturing of metals is applied to calculating the areal surface roughness, Sa, average ablation depth, Da, and Wenzel roughness factor or adhesion area ratio, r, for a range of representative cases relating to adhesion and wettability. Optimisation of the laser scanning strategy, number of laser passes and focused spot size is performed by considering the ratio of increases in Sa and r with respect to the average ablation depth: and where Highest values of and are achieved where the pulse separation distance is equal to the focused spot size in both the scanning and lateral directions. Increases in Sa, r and can be achieved by performing multiple laser passes, while r and can be increased independently of Sa and by reducing the focused laser spot size. These results suggest that r and Sa can be optimised effectively and independently in line with a given application. Finally, laser texturing experiments are performed on AA 6082 aluminium alloy and 316L austenitic stainless steel specimens with the aim of confirming model outcomes, after which tensile tests are performed on adhesive-bonded joints prepared with the same laser treatments. Further to demonstrating the benefits of laser texturing, it is shown that optimum results are not necessarily associated with a single value of Sa or r, but are instead a compromise between maximising these parameters and limiting the ablated volume.