Effect of Post Weld Heat Treatment on Residual Stress and Mechanical Properties of 106 mm Thick TC4 Titanium Alloy Electron Beam Welded Joints

doi:10.1007/s40195-025-01851-z

Abstract

Abstract:

This study analyzed through-thickness distribution of residual stress in a 106 mm ultra-thick TC4 titanium alloy electron beam welded (EBW) joint after post weld heat treatment (PWHT) using X-ray diffraction (XRD) and deep-hole drilling (DHD) methods, and investigated the microstructure and mechanical properties. During the PWHT at 600 °C, a phase transformation (β → α) occurred in the EBW joint and affected the residual stress distribution and mechanical properties. The surface residual stress was mainly compressive stress, while the internal residual stress was mainly tensile stress in the welded joint. For the as-welded joint, the absolute value of surface residual stress was higher than the absolute value of internal residual stress. After PWHT, the residual stress in the treated joint was substantially reduced compared to the as-welded joint, particularly the surface stress, which relieved from − 425 to − 90 MPa. However, the residual stress relief effect had minimal positive impact on the internal region at 600 °C. PWHT resulted in a shift of the joint fracture location from the fusion zone (FZ) to the base metal (BM), and therefore exerted no noticeable effect on the joint strength, but increased the joint elongation significantly. This study provides valuable insights into the regulation of residual stress distribution of ultra-thick titanium alloy plates.

Key words: Titanium alloy, Electron beam welding, Residual stress, Post weld heat treatment, Mechanical property

Yunlu Jiang, Lihui Wu, Dingrui Ni, Hongbo Zhao, Xu Han, Peng Xue, Bolv Xiao, Zongyi Ma. Effect of Post Weld Heat Treatment on Residual Stress and Mechanical Properties of 106 mm Thick TC4 Titanium Alloy Electron Beam Welded Joints[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(7): 1083-1094.

Figures/Tables 15

Fig. 1 Schematics diagrams of sampling location from joint

Table 1 Optimized welding parameters of EBW

Voltage, U (kV)	Velocity, V (mm min⁻¹)	Beam current, I_b (mA)	Scan amplitude (s/mm)	Scan frequency, F (Hz)
150	150	200	0.6	200

Fig. 2 Procedure of DHD method: a low-feeding EDM of reference hole, b measurement of reference hole, c EDM trepanning core, d remeasurement of reference hole

Fig. 3 Macroscopic appearance of welded joint

Fig. 4 a Macrograph of EBW joint; SEM magnified images of regions b B, c C, d D, e E, f F, g G in a

Fig. 5 SEM images of a HAZ near BM, b HAZ near FZ, c FZ in as-welded joint; d HAZ near BM, e HAZ near FZ, f FZ in PWHT joint

Fig. 6 IPF of a FZ, b HAZ near FZ, c HAZ near BM in as-welded joint; d FZ, e HAZ near FZ, f HAZ near BM in PWHT joint

Fig. 7 Phase distribution of EBW joint: as-welded condition a FZ, b HAZ outward 2 mm, c HAZ outward 10 mm; PWHT condition d FZ, e HAZ outward 2 mm, f HAZ outward 10 mm

Fig. 8 Pole figures of as-welded and PWHT joint

Fig. 9 Surface residual stress of a as-welded and b PWHT joints

Fig. 10 Internal residual stress of EBW joint: as-welded condition a FZ, b FZ outward 2 mm, c FZ outward 10 mm; PWHT condition d FZ, e FZ outward 2 mm, f FZ outward 10 mm

Fig. 11 Engineering stress-engineering strain curves of a as-welded and b PWHT joints

Fig. 12 Macro-and micro-morphologies fracture surfaces of EBW joint: a macro-morphology, b, c microstructure morphologies of as-welded joint; d macro-morphology, e, f microstructure morphologies of PWHT joint

Fig. 13 A simple model of PWHT influencing parallel stress evolution in different stage: a original stage, b welding stage, c cooling stage, d PWHT stage

Fig. 14 Fracture cross section of crack propagation path of the as-welded a-c and PWHT joint d-f

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