Microstructure Evolution and Fracture Mechanisms in Electron Beam Welded Joint of Ti-6Al-4V ELI Alloy Ultra-thick Plates

doi:10.1007/s40195-025-01872-8

Abstract

Abstract:

It is rather difficult for titanium alloy ultra-thick plates to achieve superior weld formation and excellent mechanical properties along the weld penetration direction due to the large fluctuations of the molten pool, largely limiting their engineering application. In this study, 106-mm-thick Ti-6Al-4V ELI alloy plates were successfully butt welded via electron beam welding (EBW). The defect-free EBW joint with full penetration was obtained. The precipitated secondary α (α_s) in heat affected zone (HAZ), α lamellae in fusion line (FL) and α′ martensite in fusion zone (FZ) increased the α_s/β, α/β and α′/β interfaces, respectively, resulting in the higher microhardness and impact energy values (57 J in the HAZ, 62 J in the FL and 51.9 J in the FZ) than those in the base material (BM). The impact energy of the joint in this study was higher than that for Ti-6Al-4V ELI alloy joints as reported, which was mainly attributed to the formation of the relatively thicker α phase and finer interlamellar spacing in this study, enhancing the resistance to crack propagation. Furthermore, the average fracture toughness (90.2 MPa m^1/2) of the FZ was higher than that of the BM (74.2 MPa m^1/2). This study provides references for the welding application of titanium alloy ultra-thick plates in the manufacture of large-sized components.

Key words: Ti-6Al-4V ELI alloy, Electron beam welding, Microstructure, Mechanical properties

F. S. Li, L. H. Wu, Y. Kan, H. B. Zhao, D. R. Ni, P. Xue, B. L. Xiao, Z. Y. Ma. Microstructure Evolution and Fracture Mechanisms in Electron Beam Welded Joint of Ti-6Al-4V ELI Alloy Ultra-thick Plates[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(8): 1317-1330.

Figures/Tables 13

Fig. 1 Schematics of a the welding process and b test samples

Fig. 2 Typical macrographs of the weld surfaces and cross sections of the EBW joints of Ti-6Al-4V ELI alloy ultra-thick plates at beam currents of a, b 140 mA and c, d 170 mA

Fig. 3 Typical macrographs of a weld surface and b cross section of the EBW joint at the beam current of 200 mA

Fig. 4 SEM magnified micrographs of the BM and EBW joint in zones: a A, b-d B, e C, f D, g E, and h F in Fig. 3b

Fig. 5 EBSD analysis of the BM and HAZ

Fig. 6 EBSD analysis of the FL and FZ

Fig. 7 TEM images of a top, c middle and d bottom layers of the FZ in zones D, E and F in Fig. 3b; b selected area diffraction pattern, e TEM magnified micrograph and f-h element distributions of α′ martensite

Fig. 8 Microhardness profiles along center line through thickness direction

Fig. 9 a Impact energy and b fracture toughness of the BM and EBW joint

Fig. 10 Residual stresses of the EBW joint in different directions after welding: a longitudinal stress, b normal stress along and c transverse stress

Fig. 11 Models of the welding temperature field of a cross section and b side view of the EBW joint

Fig. 12 Schematics of the flow behavior of molten pool and microstructure evolutions during welding process

Fig. 13 Fracture surfaces and crack propagation paths of the BM and FZ

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