Abstract
The effect of Si on brittle interfacial phases and microstructural evolution of Ti/Al joints was investigated during pulsed current gas tungsten arc welding (PCGTAW) with filler wires. Interfacial microstructure and phase constituents were characterized by an optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The microstructural evolution mechanism was revealed from the perspective of the thermodynamics. It was found that the layered microstructure consisted of various Ti-Al or Ti-Si intermetallic compounds (IMCs). The effect of silicon on the reaction mechanism of fusion-welding interface mainly included that the formation of Ti₅Si₃ consumed most molten titanium and suppressed the reaction of titanium with aluminum. Moreover, the Ti₅Si₃ distributing at the grain boundary contributed to the forming of discontinuous TiAl₃. The effect of silicon on the reaction mechanism of brazed interface was mainly reflected by silicon in the reaction of titanium with aluminum and the forming of Ti(Al_xSi_1–x)₃.

Key words
effect of Si, interface, microstructural evolution, welding, Ti/Al

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