Study on welding characteristics of TC4/Grade 5/Ti6AL4V titanium alloy narrow gap laser-filled stranded strand welding wire

TC4/Grade 5/Ti6AL4V Titanium alloy has the advantages of low density, high specific strength and corrosion resistance, and has been widely used in aerospace, Marine engineering, biomedicine and other fields. With the rapid development of China's infrastructure, the demand for high-quality TC4/Grade 5/Titanium 6AL4V alloy welding components is becoming more and more urgent, and higher requirements are also put forward in terms of production efficiency, service performance and assembly accuracy.

The commonly used welding methods for thick wall titanium alloys mainly include non-MIG gas shielded welding, electron beam welding, laser welding and laser arc composite welding, etc. However, the above welding methods have problems such as low welding efficiency, limited welding component size, low welding groove type and size tolerance, and large stress and strain of welded joints. At the same time, the defects of the welded joint such as coarse grain and wide heat affected zone seriously affect the strength and toughness of the welded joint. Compared with the above traditional welding technology, narrow gap laser wire welding has many advantages such as small welding heat input, narrow heat affected zone, unrestricted welding component size, high welding efficiency, low stress and strain, etc. At the same time, filling welding wire to supplement the burned alloy and beneficial alloying elements can further optimize the microstructure and properties of welded joints, so it has been widely concerned in the field of titanium alloy welding.

Thick wall materials are prone to defects such as poor side wall fusion and welding porosity in the welding process. In response to the above problems, technicians carried out related research, such as Dittrich et al., respectively, with 4 kW multi-mode fiber laser and 5 kW single-mode fiber laser, narrow gap laser wire filling welding was carried out on the 6 series aluminum alloy thick plate with a diameter of 1.6 mm AlSi12 welding wire. It is found that there are more pores in the weld, but the number of pores in single-mode laser is much less than that in multi-mode. When Kawahito et al welded stainless steel with laser wire filling, porosity was generated due to the instability of the deep melting keyhole. X-ray and high-speed camera observation found that the deep melting keyhole was subjected to the action of heat and force in the rapidly stirring melting pool, and the keyhole root was easily destabilized instantly, causing the metal steam and the protective gas in the keyhole and a small amount of air to become involved in the melting pool and form bubbles. Finally, the porosity defect is formed due to the rapid cooling of the molten pool. Huang et al. found that the defocusing amount is a direct factor affecting the stability of laser keyhole during laser wire filling welding of 9Ni steel, and indirectly determines side wall fusion and weld formation. Wu Pengbo and Xu Kai et al. introduced 3 kW laser on the basis of aluminum alloy stranded wire MIG welding to analyze the influence of laser on stranded wire MIG welding under different droplet transition conditions, and found that laser can improve the stability of stranded wire welding process and greatly expand the process range of stranded wire MIG welding. Wang et al. used aluminum alloy stranded welding wire for CMT additive manufacturing, and found that when the welding current was 140~150 A, welding voltage was 18~20 V, and welding speed was 10 mm/s, the additive manufacturing deposition layer had no obvious defects, and the grain was equiaemic. The average tensile strength and yield strength of the deposited layer are 19.8% and 22.5% higher than those of the cast aluminum alloy, respectively.

On the basis of the above research, the author carried out narrow gap laser wire filling welding of TC4/Grade 5/Titanium 6AL4V material, using 1×3 structure TC4/Grade 5/Titanium 6AL4V alloy stranded welding wire as the filling metal, using a single variable control method, to study the influence of process parameters on the side wall fusion and weld formation of laser wire filling welding head. It lays a theoretical foundation for the development of narrow-gap single-pass multilayer welding technology of titanium alloy thick plate, and promotes the wide application of narrow-gap laser wire filling welding technology and stranded wire materials in thick wall titanium alloy.