Effect of pulse frequency on microstructure and properties of Ti-6Al-4V by ultrahigh-frequency pulse gas tungsten arc welding

An experimental program of welding a titanium alloy, Ti-6Al-4V, was carried out using ultrahigh-frequency pulse gas tungsten arc welding (UHF-GTAW). The characteristics of the welds were investigated, such as the defection, microstructure, and mechanical properties. The experimental results show that the high pulse frequency reduces the heat input from the UHF-GTAW process, while gaining one-side welding with backing as a precondition. Basketweave and long acicular alpha' martensite only existed in some areas of the FZ (fusion zone) with both low uniformity and distribution density (8.4 %) as a result of conventional GTAW processes. With a pulsed current, basketweave and short acicular alpha' martensite were distributed in the FZ evenly. Short acicular alpha' martensite could be detected within the parallel long acicular alpha' martensite in the CGR when f > 30 kHz. Plastic weld joints were characterized by both the elongation, A, and the percentage of the area reduction, Z, and were optimized with a high pulse frequency. Ideal mechanical properties of the joints were achieved with an A of 68 % and a Z of 150 % with f = 30 kHz. The integrated effects of the pulse frequency and the heat input are the key factors for determining the microstructure morphology and the mechanical properties.