A two-component epoxy resin (Leuna-Harze GmbH, Leuna, Germany), was employed as the adhesive (Table 2). The low viscosity of the resin allowed access to the cavities of the substrates, which were produced during the laser pre-treatment.
Properties of the used adhesive provided by the Leuna-Harze GmbH.Resin Epilox T19-34Hardener TetaColourColourlessColourlessViscosity at 20 °C/mPa s300–40030Density (g/cm³)1.140.98Epoxy and amine equivalent weight (g/equiv.)160–17524Amine value (mg KOH/g)–1400Full-size tableTable optionsView in workspaceDownload as CSV
2.2. Laser pre-treatment
Pieces of the aluminium alloys were treated with CCG-1423 pulsed ytterbium-doped fibre laser CL 50 (Clean-Lasersysteme GmbH, Herzogenrath, Germany). The laser process settings are given in Table 3. The excellent quality of the Gaussian-shaped laser beam profile allowed focusing the beam (λ=1060–1070 nm) diameter between 16 µm and 50 µm. Due to the short pulse duration of a few nanoseconds, a maximum pulse power of 20 kW can be achieved, which is in contrast to the relatively low average laser power of a theoretical maximum of 50 W. The energy density that was introduced into the material was sufficient to sublimate near surface layers, form a fresh mountain-like aluminium oxide layer and purify the surface in one step. Dust-like side-products of the laser treatment were vacuumed or mechanically removed from the surface.