*2.2. Design of the Joint*

The frame was entirely joined by a manual welding MIG. Different samples were obtained from cross sections of the components and can be summarized as follows:


Additional samples made from the bars joining were realized in order to investigate a wider mixture of couplings, as follows:


In addition, the comparison on a simpler geometry is useful to avoid potential influence on the results related to the different and complex shapes of the welding in the various sections of the frame. Each above-mentioned combination was welded with three different techniques: MIG, CMT, and the fiber laser-MIG hybrid. Thus, nine different kinds of samples were analyzed: three materials matching and three welding processes. The bars used were 3 mm thick with dimensions of 100 × 25 mm, as shown in Figure 2. Full penetration joints with zero gap were achieved and the welding direction was parallel to the sample's axis. Before welding, the oxide films were removed by using emery cloth and acetone. The welding machines used were the TPS 320i, Fronius RCU 5000i(Fronius Italia S.r.l., Verona, Italy), and TS 4.20 2D (TTM LASER SPA, Brescia, Italy) for the MIG, CMT, and fiber laser-MIG hybrid joints, respectively. All joints were performed in a protective argon atmosphere with a robotic setup and without preheating. A welding current of about 130–140 A and a welding voltage of approximately 18–20 V with a wire feeding rate of 6–8 m/min were used for MIG and CMT. The gas flow rate was 14.5, 15, and 20 l/min for MIG, CMT, and fiber laser-MIG hybrid joints, respectively. A wobble circular pattern with the speed of 8–10 mm/s and laser power of 3–4 kW was used for the fiber laser-MIG hybrid welding to achieve a wider weld beam and reduce the porosities. The wobbling frequency was about 100 Hz with amplitude of 40◦ and the torch angle from the surface was around 85◦.

**Figure 1.** Samples obtained from the sub-frames: (**a**) extruded (6082-T6)-extruded (6082-T6) welds, (**b**) extruded (6082-T6)-cast (EN AC 42100-T6) welds.

**Figure 2.** Example of the samples used for the different weld techniques.
