A two-step full laser surface treatment to improve the adhesive bonding of aluminium-aluminium joints

To improve the adhesion between Aluminium-Aluminium joints, a two-step laser surface treatment was developed and tested, adopting a 30W pulsed Yb:YAG nanosecond laser source. The process consists of a first phase, called laser texturing, where a deep texture is obtained on the adherents by adopting high pulse energy and several repetitions, followed by a further laser treatment, called laser cleaning, carried out with lower energy content, and applied over the overall adhesion surface. To characterise the treatment process, the effects of technological parameters on texturing geometry were first investigated to select the proper texture; then, textures with different selected geometries were carried out and adopted to produce single lap joints according to the ASTM D1002-10 Standard. An epoxy system adhesive was adopted for the joining. Furthermore, samples with only one-step treatment (i.e. only laser texturing or laser cleaning), standard treatment (sandpaper), and acetone cleaning were fabricated and adopted as reference samples. Analysis of variance was applied to study the effect of the process parameters, and digital image analysis was adopted to evaluate the percentage of adhesive/cohesive failure. From the results, compared to the only textured reference samples, the two-step laser treatment increases the apparent shear stress regardless of the adopted texture geometry. Moreover, it was found that only laser cleaning treatment can significantly improve joint strength compared to the untreated sample.