Microstructure and Mechanical Property of the Welding Joint of TA1/Cu/ X65 Trimetallic Sheets
Min ZHANG(), Erlong MU, Xiaowei WANG, Ting HAN, Hailong LUO
School of Materials Science and Engineering, Xi'an University of Technology, Xi'an 710048, China
Cite this article:
Min ZHANG, Erlong MU, Xiaowei WANG, Ting HAN, Hailong LUO. Microstructure and Mechanical Property of the Welding Joint of TA1/Cu/ X65 Trimetallic Sheets. Acta Metall Sin, 2018, 54(7): 1068-1076.
Titanium and its alloys with fine corrosion resistance and specific tenacity are widely used in the fields of astronautics, chemical industry and so on. While the pipeline steels with low price and good mechanical properties are always used in petroleum industry. For now, composite panels are widely used in petrochemical industry, aerospace engineering and other fields, which can combine the respective features of the dissimilar materials together so as to meet the special requirements and save a lot of rare and precious metals. Previous studies have showed that the joining of titanium and steel suffered from two major challenges: one was the emergence of continuous distributed intermetallics of TiFe and TiFe2 in the weld, which could cause brittle fracture with low strength; the other was the occurrence of residual stresses that were caused by the great differences in thermal properties between titanium and steel. This work is aimed to join the explosion-bonded TA1/Cu/X65 trimetallic sheets (titanium flyer plate with thickness 2 mm, copper intermediate plate 1 mm, and X65 base plate 12 mm) with Cu-based flux-cored wires by the tungsten inert gas (TIG) welding. The microstructure and mechanical properties of welded joint was characterized by using SEM, EDS, TEM, XRD and tensile and microhardness tests. The results indicated that the filler metals for each weld layer have obvious zoning by using solid solution phases and intermetallic compounds. There was about 150 μm width Ti-Cu reaction zone between the Ti weld and transition layer weld. The microstructures of Cu-Ag-Mo-Nb/ER50-6 transition interface were composed of Fe-based and Cu-based solid solution. The intermediate copper played an important role in reducing the high temperature residence time of welded joints so as to reduce the interdiffusion of Ti, Fe element. Consequently, the hard-brittle Ti-Fe intermetallic compounds were partly replaced by Cu-based solid solution and Ti-Cu, Ti-Ag intermetallic compounds with relatively good ductility and toughness. The average tensile strength of the butt joints is 507 MPa at room temperature, mainly of that of X65 was obtained. ERTi-1 weld metal exhibited higher hardness than Cu-Ag-Mo-Nb weld metal, and their microhardness values were 507 and 447 HV100, respectively. In addition, the microhardness in reaction zone presented a slightly drop. The lowest values occurred in ER50-6 weld metal.
Fund: Supported by National Natural Science Foundation of China (No.51274162), Key Laboratory Project of Education Department of Shaanxi Province (No.15JS082) and Service Local Project of Education Department of Shaanxi Province (No.16JF021)
Fig.1 Groove dimensions of the welded plate (The blue rhombus are microhardness test points)
Material
C
Mn
Si
Ti
Cu
Fe
O
N
H
S
P
TA1
0.015
-
-
Bal.
-
0.023
0.07
0.005
0.001
0.005
0.005
T2 (copper)
-
-
-
-
Bal.
0.005
-
-
-
0.005
0.005
X65
0.09
1.32
0.22
-
-
Bal.
-
-
-
0.005
0.019
Table 1 Chemical compositions of materials applied (mass fraction / %)
Welding material
D / mm
I / A
U / V
v / (mmmin-1)
Q / (Lmin-1)
ER50-6
1.2
100~120
16~18
150~200
15~20
180~200
20~23
250~350
15~20
Cu-Ag-Mo-Nb
1.2
90~110
16~18
150~250
15~20
ERTi-1
1.2
100~120
14~16
90~110
15~20
Table 2 The welding parameters of TA1/Cu/X65 trimetallic sheets
Fig.2 Microstructures of the welded joint (Figs.2b~j are respectively corresponding to the area marked with numbers 1~9 in black boxes in Fig.2; the points A~T indicated by a black arrow are tested by EDS; WM—welding material)(a) cross-section morphology (b) TA1/Cu-Ag-Mo-Nb/Cu interface (c) TA1/Cu-Ag-Mo-Nb interface(d~g) ERTi-1/Cu-Ag-Mo-Nb interface (h) X65/Cu-Ag-Mo-Nb/Cu interface(i) X65/Cu-Ag-Mo-Nb interface (j) ERTi-1 weld metal
Fig.3 XRD spectrum in the weld of TA1/Cu/X65 trimetallic sheets
Point
Ti
Cu
Fe
Ag
Mo
Nb
Possible phase
A
86.44
11.19
1.22
0.72
0.19
0.25
β-Ti(s, s)+Ti2Cu
B
51.90
46.73
-
0.98
0.21
0.18
TiCu
C
84.49
13.44
1.10
0.65
0.32
-
β-Ti(s, s)+Ti2Cu
D
67.29
31.88
0.35
0.32
0.05
0.10
Ti2Cu
E
67.29
33.22
0.64
0.42
0.21
0.08
Ti2Cu
F
83.79
13.58
2.10
0.32
0.11
0.10
β-Ti(s, s)+Ti2Cu
G
63.04
30.04
1.62
4.13
0.03
1.14
Ti2Cu+TiCu
H
60.62
32.99
3.85
1.24
1.26
0.04
Ti2Cu
I
39.12
50.01
10.32
0.32
0.13
0.10
Cu0.8Fe0.2Ti
J
7.53
87.41
0.52
4.29
0.16
0.08
Cu(s, s)+TiAg
K
46.75
45.08
4.20
2.31
1.02
0.64
TiCu
L
16.21
82.14
0.62
0.40
0.40
0.23
Cu(s, s)+TiCu4
M
11.19
86.44
1.22
0.72
0.19
0.25
Cu(s, s)+TiCu4
N
14.89
6.94
76.14
0.49
1.14
0.39
Fe(s, s)+TiFe
O
11.74
11.95
66.78
4.21
2.89
2.43
Fe(s, s)+TiCu
P
37.17
48.77
11.43
1.11
0.04
1.49
Cu0.8Fe0.2Ti
Q
1.02
92.36
6.50
0.08
-
0.04
Cu(s, s)
R
15.58
9.21
68.52
6.52
0.12
0.05
Fe(s, s)+TiCu
S
74.32
24.44
1.02
0.13
0.05
0.04
β-Ti(s, s)+Ti2Cu
T
93.99
5.33
0.38
0.21
0.04
0.06
β-Ti(s, s)
Table 3 Chemical compositions of points A~T marked in Fig.2 (atomic fraction / %)
Fig.4 TEM images and corresponding SAED patterns (insets, marked by black circles) of ERTi-1/Cu-Ag-Mo-Nb interface (a) and X65/Cu-Ag-Mo-Nb/Cu interface (b)
Fig.5 Stress-strain curves and fractured samples (inset) for tensile test of the joint
Fig.6 Fracture morphologies of the welded joint (Figs.6b~e are corresponding to the areas marked with letters b~e in a black box in Fig.6a)(a) global view of the fracture (b) ERTi-1 weld metal (c) ERTi-1/Cu-Ag-Mo-Nb reaction zone (d) Cu-Ag-Mo-Nb/ER50-6 (e) ER50-6 weld metal
Fig.7 Microhardness distributions of the welded joint(a) vertical to the ERTi-1, Cu-Ag-Mo-Nb and ER50-6 weld metal (Ti-Cu IMC: Ti2Cu、TiCu、Cu0.8Fe0.2Ti、TiCu4)(b) across the interface of the trimetallic sheet
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