Analysis on the technology, microstructure, and mechanical properties of Ti-6Al-4 V alloy narrow gap oscillation laser welding with multi-stranded wire.

In this paper, multi-stranded wires were used as the filling material for narrow gap oscillation laser wire filling welding of thick-walled titanium alloy. The effect of laser beam oscillation frequency and diameter on weld formation and welding defects was investigated. By using a high-speed camera, the melting process of the laser-melted multi-stranded wires was observed. The macrostructure and microstructure of the welded joint were analyzed using the optical microscope (OM), scanning electron microscope (SEM), electron back scattering diffraction (EBSD), and transmission electron microscope (TEM), and the mechanical property tests were also carried out. The results showed that the droplet was in the liquid bridge transition mode, while the oscillation diameter of the laser beam was 2 mm, and the frequency was 100 Hz. The obtained weld seam was continuous and stable, without pores and incomplete sidewall fusion. The base metal (BM) of the welded joint was composed of equiaxed α + β phase, the heat-affected zone (HAZ) was comprised of acicular α′ martensite and primary αp phase, and the welded metal (WM) consisted of coarse original β columnar grains and internal basketweave acicular α′ martensite. The microhardness of the WM was the highest. The average tensile strength of the welded joint reached 940 MPa. The tensile fracture occurred at BM. The fracture dimple was relatively deep, presenting the characteristics of ductile fracture. The average impact toughness of the welded joint was 12 J. The fracture dimple was shallow, appearing as a ductile fracture. [ABSTRACT FROM AUTHOR]