*2.3. Friction Welding*

At first, the geometries presented above were cleaned in an ultrasonic bath filled with ethanol. After drying, these were friction-welded on a KUKA Genius Plus (Kuka AG, Augsburg, Germany). The most important process parameters are listed in Table 3. The parameters were selected according to prior investigations. For comparability, most parameters were chosen to be identical or limited to a few varying values according to the different geometries. Parameters with varying values were selected since these resulted in similar shapes and qualities of the bonding, according to first visual examinations.

The major differences between the performed welding processes of the first four geometries and the second four are the following: The friction speed was increased from 1500 to 2000 rpm for Geometries E, F, G and H to ensure a convenient heat generation at lower friction forces. Lower frictional forces were chosen for the second four geometries to prevent undesired deformations during the friction phase. In order to investigate the influence of high true strain, the friction path of Geometry H was increased in comparison to the path-controlled processes of Geometries A and F.
