PSI - Issue 47

A. Califano et al. / Procedia Structural Integrity 47 (2023) 842–848 Author name / Structural Integrity Procedia 00 (2019) 000–000

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aeronautic and aerospace fields, in which extremely precise and strong joints are needed for constituting reliable components and sub-components made in high-performing materials, such as Ti-based alloys (Quazi et al. (2020)). Nevertheless, LBW for Ti-based alloys is a complicated process due to uneven temperature, non-uniform chemical composition and stress. Furthermore, change in the heat input affects the weld microstructure and mechanical properties due to poor thermal conductivity of titanium alloys (Auwal et al. (2018)). Moreover, the cost of laser welding is higher than that of the traditional processes, to not count that accurate beam/joint alignment and surface preparation are mandatory for obtaining a good quality weld (Caiazzo et al. (2015)). Among the Ti-based alloys, the Ti6Al4V is perhaps the most used and preferred for its excellent mechanical properties, low specific weight, and high corrosion resistance. However, if, on one hand, traditional welding techniques (plasma arc (Gao et al. (2021)), electron beam welding, TIG (Omoniyi et al. (2021))) are conventionally and widely used to join Ti6Al4V, on the other hand, LBW has been receiving an ever-increasing interest only in recent years (Boccarusso et al. (2017)). Lately, the mechanical properties of laser-welded Ti6Al4V joints have been investigated and it has been observed that the welding parameters have a significant impact on microstructures, mechanical properties and welding defects (Akman et al. (2009)). Cao and Jahazi, (2009) found out that the HAZ width decreases with increasing welding speed and that, compared to the parent material, the final joint obtained from two Ti6Al4V alloy sheets has a slightly higher strength with reduced ductility. Xu et al. (2020) focused their attention on the effects of the defocusing distance and the welding speed on transverse weld geometry, highlighting that both parameters could be optimized in order to limit the geometry defects. LBW butt joints in Ti-6Al-4V were also investigated under different welding regimes (Squillace et al. (2012)) showing that an underfill defect was always present, being its characteristics dependent from the specific heat input. Different welding conditions have been also explored by Kumar et al. (2017) concluding that the welding speed has the highest impact on the mechanical behavior of joints, followed by laser beam power and by laser position finally. Within this framework, the current work was based on preliminarily investigating the static tensile behavior of Ti6Al4V laser welded single lap joints. In particular, joints with different combination of welding parameters (i.e. laser power, laser speed and laser focus) were obtained and the related specimens were experimentally tested. The final goal was comparing the mechanical properties of the different specimens and gaining insights about the effect that the different welding parameters used for obtaining the original joints have on them.

Nomenclature HAZ

Heat-Affected Zone LBW Laser-Beam Welding S1 Strain-gauge 1 S2 Strain-gauge 2 TIG Tungsten Inert Gas

2. Materials and Methods The case studies are single-lap joints obtained by welding two plates of Ti6Al4V having sizes 200 mm x 100 mm x 3 mm. In detail, twelve joints were obtained by varying the following laser welding parameters: • laser power, equal to 3 kW for all joints; • welding speed, equal to 30 mm/s, 35 mm/s or 40 mm/s; • laser beam focus, equal to 0 mm or -3 mm. The twelve joints were subdivided into six classes (from A to F), according to the fixed tern of parameters chosen for the welding phase (Table 1); this means two joints for tested for each class and identified as it follows: A1, A2, B1, B2, C1, C2, D1, D2, E1, E2, F1 and F2.