Microstructure and mechanical properties in ultrasonic-magnetic field coaxial hybrid GTAW joints of Ti-6Al-4V

Abstract

GTAW has less arc energy density and coarse joint microstructure. A novel method of Ultrasonic-Magnetic field coaxial hybrid GTAW (U-M-GTAW) was proposed, which improved upon the traditional GTAW torch. Under 140 A current and 4 mm/s speed, the results indicated that the U-M-GTAW depth-to-width ratio increased by 54.5 % compared to GTAW. Meanwhile, the surface of the joint showed a dense corrugation. The interior of the joints was all composed of martensite α', whose phase transformation obeyed the Burgers orientation relationship. The average martensite length in the U-M-GTAW weld zone was 14.8 μm, which was 33.6 % shorter than GTAW, and the length distribution was more uniform. Additionally, the U-M-GTAW joint orientation shifted from {01−10} to {−12−10}, revealing a higher texture density. The substantial precipitation of martensite in the weld zone resulted in the highest hardness, with an average microhardness of 396.8 ± 9.0 HV, marking a 12.1 % improvement over base metal. Moreover, U-M-GTAW exhibited an elongation of 9.3 %, representing a 10.7 % enhancement compared to GTAW, with deeper dimples in the fracture indicating superior plasticity. Notably, the improvements in microhardness and elongation in U-M-GTAW were primarily attributed to the reduction in martensite length and its uniform distribution under the action of ultrasonic and magnetic fields.