PSI - Issue 50

Aleksandr Malikov et al. / Procedia Structural Integrity 50 (2023) 170–177 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

174

5

The optimal conditions for obtaining defect-free welded joints in laser welding with wire are: laser radiation power W =3 kW, welding speed V = 2 m/min, wire feed speed S = 2 m/min and focus position ∆ F = -3 mm from the upper sheet boundary. Fig. 3 shows an optical image of a cross section of a weld taken under optimal welding conditions.

Fig. 3. The microstructure of the cross section of a weld with a wire.

The diameter and depth of the focal spot were determined. Laser radiation was focused using a ZnSe lens with a focal length f = 254 mm. The diameter of the laser radiation incident on the lens is D=30 mm. According to the formula d= (4  f/  DK+kD 3 /f 2 ) where the wavelength of laser radiation is λ =10.6 μm , the scale factor of the lens material is k = 0.0187, the quality factor of laser radiation is K=0.7, the diameter of the focused beam at the focus is ≈ 168 μm for this type of CO 2 laser. Focal spot depth z=2fd/D ≈2.84 mm. The intensity of laser radiation at a power of 3 kW is 1.4 * 105 W / mm2. The energy conditions for obtaining a high-quality weld with wire were estimated (laser radiation power W = 3 kW, welding speed V = 2 m / min, shielding gas consumption G =5 l / min, focus position ∆ F = -3 mm, focu sed beam diameter at focus ≈ 168 µm, and focus depth 2.84 mm, weld height t≈1.71 mm, average weld width h ≈1.82 mm): heat input equal to the ratio W/V was ≈ 90.9 J/mm, energy per unit volume of the molten material, equal to W/Vth, was ≈ 28.94 J/mm3. High strength can be achieved due to a well-balanced formation of coherent and subsequent semi-coherent Al precipitates of Guinier – Preston zones and metastable particles of intermetallic phases, which serve as an obstacle to the movement of dislocations. Dislocations moving during plastic deformation cut the Guinier – Preston zones and metastable particles, however, the elastic deformations that exist around the zones, the disruption of the order in the arrangement of atoms when dislocations pass through the zones, cause an increase in the stress necessary for the movement of dislocations. When the weld melt solidifies, the formation of phases at the boundaries of subgrains can be due to nonequilibrium crystallization, i.e. diffusion processes in the liquid phase. Figure 4 shows X-ray diffraction patterns of samples with a welded joint before and after thermal post processing, obtained using synchrotron radiation in transmission geometry.