*2.3. Microstructure Characterization*

In order to analyze the defects and microstructures of the joints, the different welded samples were examined using a Leica DMI 5000M (Leica Microsystem, Milan, Italy) optical microscope and LEO EVO-40 XVP Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectrometers (EDS) (LEO EVO 40, Carl Zeiss AG, Milan, Italy). The welds were observed using the Leica Application Suite (LAS 4.0, Leica Microsystem, Milan, Italy), which is an image processing software tool for image analysis that integrates a Leica automated microscope and digital camera. For metallographic observations, transversal sections of the samples were prepared with standard metallographic techniques (ground with SiC papers and polished with 1 μm diamond paste). The samples with the extruded part were etched with Keller's reagent in order to better investigate the defects and microstructures.
