Research On Technology And Interfacial Characteristic Of Tig Welding-brazing Of Precoating Titanium Alloy To Aluminum Alloy

Titanium reacts with aluminum to form brittle intermetallic compounds (IMCs)due to their incompatible metallurgical weldability and the thick IMCs decreasemechanical properties of joints. So high quality joining of Ti/Al hybrid structureshas always been one of the hot research topics in welding field. Nowadays, arcwelding-brazing, which has advantages on equipment costs and applied scopes, isgradually concerned. However, two major problems, including the poorspreadability of filler metal on Ti substrates with TIG heating and the formation ofvast IMCs at the interface, retard its research and application on joining of Ti/Alhybrid structures. Therefore, TIG welding-brazing of precoating-Ti and Al alloy waspresented to obtain high quality joints. Aluminum coating on titannium alloy wasapplied to promote solder wetting and suppress IMCs growth.This paper has developed systemic research on butt joining of precoating-Ti/Aldissimile alloys with arc welding-brazing technique. Firstly, a thin layer ofaluminum was plated on the surface of titanium alloys through hot-dipping.Interfacial characteristics between coating and titanium substract have beenobserved and analyzed. And the reaction layer forming rules were calculated bythermodynamic analysis method. Then, a novel technique, referred to precoating-Ti/Al dissimilar alloys arc welding-brazing, was presented based on the analysis offiller’s spreading experiments. A good weld forming of joints was achieved byadjusting the heat input, heating location and filler patterns. Microstructures ofwelding-brazed joints were observed and the mechanical properties of the jointswere evaluated by tensile and hardness tests. At last, the research was focus on theeffect of precoating on welding procedure and interface layers.The results showed that metal plating solutions could spread on the surface oftitanium easily with the effect of flux. The wetting procedure exhibited four stagesincluding nonwetting, bottom wetting, wetting stretchs and complete wetting.Reaction layer, which was detected to be TiAl3, formed between coating andtitanium substrate, and its thickness was controlled below1μm under750℃short-term immersion plating. In welding procedure, the coating facilited spread abilitiesof solder wire on titanium and increased welding speed nearly doubled. Inmetallurgical reaction process, the coating reaction layers blocked Ti atomsdiffusion into liquid Al and suppressed the growth of seam reaction layers. Thefastest welding speed was4.0mm/s and an uniform layer with a thickness below2μm was observed at the interface with pure Al filler. Due to the differences in heat input, the thickness of interfacial reaction layer decreased with the increase ofwelding speed. When Si elements was added to the wire, it gathered in reactionlayer and limited atom diffusion, furthe suppressed interfacial reaction. Meanwhile,Cu element played a certain role on interface reaction. The thin reaction layer hasimproved seam strength. Seam strength was up to260MPa with AlCu6filler,85%of LF6basemetal, and the fracture location was located in the weld.