Issue 43

F. Berto et alii, Frattura ed Integrità Strutturale, 43 (2018) 1-32; DOI: 10.3221/IGF-ESIS.43.01 25 Figure 31: Sketch, not in scale, of how the HYB's tool works the material to obtain the welding. The aluminum side is deformed by the tool while the steel side remains untouched. The welding is therefore achieved by the synergic action of two processes. The first one is the filling action of the extruded material, which will fully fill up the void between the plates, scrape off the oxide layer and deform the Al BM by shear stresses. The second is the rotating process of the spindle tool that contributes to the mixing of the FM with aluminum taken from the butt plate by the tool, which will enhance metal surface exposure. This takes the oxides issue out and promotes virgin surface contacts, as new metal is continuously exposed. Fig. 32 reveals how the upper shape of the welding presents characteristic periodic curves due to the spindle rotation. The transversal view shows the flash on the top and the clean root shape on the bottom of the joint. The beveled steel butt plate shows a clear straight welded line, not being touched by the spindle itself during the entire process. Figure 32: Upper and transversal appearance of HYB dissimilar welded plates. Aluminum on left side, steel on the right side. Figs. 33 and 34 show the details of Al-steel joints recently obtained in [147]. This new method of joining parts is very promising and the structural integrity, in particular fracture and fatigue behavior have been initially studied in [147] showing some good potential also in this sense. The design of these joints remain a challenging point that can be faced with the application of the SED approach. (a) (b) Figure 33: HYB weldments. The first with normal light (a) , the second with polarized light (b) .