Abstract In this study, Ti-6Al-4V (annealed) alloy sheet with butt joint design was welded by tungsten-gas arc welding (GTAW) process using AMS 4954G filler metal. The aim of this study was to investigate the effect of pulse system frequency on the microstructure and mechanical properties of the connection. Weld samples were eva‎luated in terms of physical properties (depth and width of the weld) and mechanical properties (microhardness test and tensile test). Optical and scanning electron microscopes were used to study the microstructure of the weld metal, base metal and heat affected areas. The experimental results showed that increasing the pulse frequency increases the cooling rate of the molten pool, which increases the amount of martensitic phase α ʹ in the form of a basket in the weld metal region and ultimately leads to an increase in the average microhardness in this area. Also, the welding sample with the highest frequency (450 Hz) mainly has a hard martensitic α ʹ basket-shaped phase, which caused the highest average hardness (367 Vickers) in the weld metal region. In the non-frequency welding sample, due to the lack of pulse current and lower cooling rate of the molten pool, large amounts of soft phases of Wiedmann Stätten layers are formed in the weld metal region, which ultimately causes the lowest average weld metal hardness (343 Vickers) among the samples.The results of tensile test showed that all samples failed in the base metal area, which gave almost similar results in terms of tensile strength (in the range of 964 to 976 MPa) and elongation percentage (10% to 11%) for all weld samples was obtained.

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