**3. Results**

The following sections present the results of the different testing methods. These include the determination of mechanical parameters as well as metallographic investigations.

## *3.1. Tensile Test*

In Figure 5 the stress–strain curve of a sample of Geometry A is exemplarily depicted on the left side and a comparison of the samples with the highest tensile strengths *Rm* is presented on the right side.

**Figure 5.** (**a**) stress–strain curve of Geometry A; (**b**) schematic drafts of the specimen geometries featuring the highest tensile strengths values with the standard deviation.

The tensile tests show that though the tensile strength *Rm* achievable with the various geometries differs, the qualitative shapes of the curves are almost identical. Fracture in the joining zone occurs due to brittleness of all geometries except Geometry A (confer Figure 6). An increased elongation at fracture is only visible in the stress–strain curve of Geometry A; here, reaching the stress maximum (Figure 5, at a strain of 0.022) a lateral contraction of the aluminum alloy can be observed.

**Figure 6.** Specimen of Geometry A after tensile testing: (**a**) cross section; (**b**) aluminum side; (**c**) steel side.

All specimens have brittle fractures. Just specimens of Geometry A have a necking (Figure 5) and more remains of the aluminum (Figure 6) than other specimens. Figure 6 shows one specimen of Geometry A after tensile testing.
