Issue 43

P. Corigliano et alii, Frattura ed Integrità Strutturale, 43 (2018) 171-181; DOI: 10.3221/IGF-ESIS.43.13 173 A V About N C H <5.5% <3.5% <0.2% <% 00:05 <% 12:08 <0.0375% Table 1 : Nominal chemical composition of the alloy Ti-6Al-4V. Laser source Wavelength Power range Beam quality Diameter of the fiber Spot diameter focus YB: YAG 1030 nm 1000-10000 W 6 mm * mrad 200 uM 300 pm Table 2 : Features of the laser source. During welding of titanium alloys, the protection of the molten bath is very problematic because, compared to other materials, titanium has a high affinity with the environmental vapors and gases at high temperatures, which leads to not acceptable characteristics of the weld toe with considerable embrittlement of the same. The importance of this is underscored in the standard AWS D17.1 / D17.1 M: 2010, which provides specifications for fusion welding for aerospace applications. The welding is prepared in two passes, so that, after the process, the fusion areas in the cross section to the advancing direction of the beam intersect ensuring the continuity of the material (Fig. 1). To achieve these joints, it is necessary that the laser beam is inclined by a suitable angle α (Fig. 2). Figure 1: T welding scheme. Figure 2: Tilt angle of the laser beam during welding. Taking into account the high susceptibility to oxidation of titanium alloys at high temperatures, it has been designed and realized in a device ad hoc for the protection and for the mounting of the plates [19]. Figure 3 : Protection and clamping system used. On the basis of previous experience [20] on butt welds, on titanium sheets and on an experimental campaign related to T welded joints, the optimal condition of the process parameters has been identified, shown in Tab. 3.