Effects of Post-weld Heat Treatment on Microstructure, Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

doi:10.1007/s40195-018-00869-w

Abstract

Abstract:

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows different microstructure and microhardness due to the different welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing effect on the weld and their existence was more of an adverse effect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.

Key words: 2219, Aluminum, alloy, Tungsten, inert, gas, arc, welding, Post-weld, heat, treatment, Weld, reinforcement, Digital, image, correlation, technique

Deng-Kui Zhang, Guo-Qing Wang, Ai-Ping Wu, Ji-Guo Shan, Yue Zhao, Tian-Yi Zhao, Dan-Yang Meng, Jian-Ling Song, Zhong-Ping Zhang. Effects of Post-weld Heat Treatment on Microstructure, Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(6): 684-694.

Figures/Tables 17

Table 1 Chemical compositions of 2219 aluminum alloy and ER2325 filler metal (wt.%)

Alloy	Si	Fe	Cu	Mn	Mg	Zn	Ti	Zr	V	Al
2219	0.2	0.3	5.8-6.8	0.2-0.4	0.02	0.1	0.02-0.10	0.10-0.25	0.05-0.15	Bal.
2325	-	-	6.0-6.8	0.2-0.4	-	-	0.1-0.2	-	-	Bal.

Table 2 Welding process parameters of the two butt-welded plate joints (η represents the power factor of the arc)

Butt-welded plate joint	Welding layer	Welding heat input, η (J·cm^-1)	Wire feeding speed (mm·min^-1)
1#	First layer	12,825	-
	Second layer	29,314	600
	Thirdlayer	37,620	800
2#	First layer	12,825	-
	Second layer	29,314	400
	Third layer	33,094	800

Fig. 1 Dimensions of tensile specimen (unit: mm)

Fig. 2 Specific post-weld heat treatment process

Fig. 3 TEM images of 2219-C10S aluminum alloy: a-c the microstructure of the different phase, respectively; d, e the selected area diffraction pattern from a, b, respectively

Fig. 4 Microstructure of WZ before and after the post-weld heat treatment: a1, a2, b1, b2, c1, c2 the upper, the middle and the lower layer of the WZ in as-welded state; d1, d2, e1, e2, f1, f2 the upper, the middle and the lower layer of the WZ after the post-weld heat treatment

Table 3 EDS analysis results of the α-Al matrix in Fig. 4 (wt.%)

No.	A ₁	A ₂	A ₃	B ₁	B ₂	B ₃	C ₁	C ₂	C ₃
Cu	3.19	3.57	2.84	3.91	4.02	3.85	2.17	2.46	2.44
Cu	Average: 3.20			Average: 3.93			Average: 2.36
Al	96.81	96.43	97.16	96.09	95.98	96.15	97.83	97.54	97.56
Al	Average: 96.80			Average: 96.07			Average: 97.64
No.	D ₁	D ₂	D ₃	E ₁	E ₂	E ₃	F ₁	F ₂	F ₃
Cu	7.83	7.51	7.64	7.88	7.77	8.61	7.72	7.81	7.79
Cu	Average: 7.66			Average: 8.09			Average: 7.77
Al	92.17	92.49	92.36	92.12	92.23	91.39	92.28	92.19	92.21
Al	Average: 92.34			Average: 91.91			Average: 92.23

Fig. 5 Microstructure of joint’s PMZ, OAZ, HAZ before and after the post-weld heat treatment: a1, a2, b1, b2, c1, c2 the region of PMZ, OAZ and HAZ in as-welded state; d1, d2, e1, e2, f1, f2 the region of PMZ, OAZ and HAZ after the post-weld heat treatment

Table 4 EDS analysis results of the α-Al matrix in Fig. 5 (wt.%)

No.	A ₁	A ₂	A ₃	B ₁	B ₂	B ₃	C ₁	C ₂	C ₃
Cu	7.91	8.04	7.93	7.73	7.67	7.94	7.96	7.44	7.79
Cu	Average: 7.96			Average: 7.78			Average: 7.73
Al	92.09	91.96	92.07	92.27	92.33	92.06	92.04	92.56	92.22
Al	Average: 92.04			Average: 92.22			Average: 92.27

Fig. 6 Microhardness distribution on transverse cross section of the joints: a, b the locations of hardness testing of 1# and 2# joints; c, d the hardness distribution of 1# joint before and after the post-weld heat treatment; e, f the hardness distribution of 2# joint before and after the post-weld heat treatment

Fig. 7 Tensile curves of the welded joints

Table 5 Tensile properties of the welded joints

Samples	Tensile strength (MPa)	Elongation (%)	Elongation after fracture (%)
1-1#	310	8.0	8.3
1-2#	309	7.6	8.0
1-3#	443	5.4	5.9
1-4#	449	7.6	7.9
2-1#	278	3.9	5.1
2-2#	270	3.7	4.1
2-3#	447	6.1	6.7
2-4#	454	7.0	7.2

Fig. 8 Macroscopic morphology on transverse cross section of fractured joints: a 1-1#, b 1-3#, c 1-4#

Fig. 9 Enlarged images of crack initiation region of fractured joints: a 1-1#, b 1-3#, c 1-4#

Fig. 10 True strain distributions on the edge surface immediately before the fracture: a 1-1#, b 1-3#, c 1-4#

Fig. 11 True strain curves of the crack initiation points during the tensile test

Fig. 12 True strain distributions on the edge surface under different stresses during the tensile test: a, b, c 1-1#, 1-3#, 1-4# specimens under stress of 300 MPa, respectively; d, e 1-3#, 1-4# specimens under stress of 430 MPa, respectively

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