Comparative Study of Bypass-Current MIG Welded-Brazed Aluminum/Galvanized Steel and Aluminum/Stainless Steel

doi:10.1007/s40195-017-0578-3

Abstract

Abstract:

A bypass-current metal inert-gas welding-brazing technology has been developed to join aluminum/galvanized steel and aluminum/stainless steel. Microstructure, intermetallic compounds and hardness distribution of the joints were studied by optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction analysis and microhardness tests. Comparative study on both types of joints was carried out. During aluminum to galvanized steel assembling, finer seam was obtained under a more stable process. A uniform interfacial reaction layer with a thickness of 2-4 μm was formed. During aluminum to stainless steel assembling, an uneven interfacial reaction layer with a thickness of 5-45 μm was formed. Intermetallic compounds at the interface of aluminum/galvanized steel were identified as Fe-Al-Si-Zn complex phases, while Fe-Al-Cr-Ni complex phases were found at the aluminum/stainless steel interface. Microhardness of interfacial layer increases rapidly within reaction layer due to possible brittle intermetallic compounds.

Key words: Aluminum alloy, Steel, Intermetallic compounds, Dissimilar joining

Yu-Gang Miao, Guang-Yu Chen, Peng Zhang, Duan-Feng Han. Comparative Study of Bypass-Current MIG Welded-Brazed Aluminum/Galvanized Steel and Aluminum/Stainless Steel[J]. Acta Metallurgica Sinica (English Letters), 2017, 30(8): 721-730.

Figures/Tables 18

Table 1 Chemical compositions of base metal and filler metal (wt%)

Material	Mg	Si	Mn	Cu	Zn	Ti	Cr	Ni	C	P	S	Al	Fe
6061 Al alloy	0.8-1.2	0.4-0.8	≤0.15	0.15-0.40	≤0.25	≤0.15	0.04-0.35	-	-	-	-	Bal.	≤0.7
Galvanized steel	-	≤0.30	0.30-0.65	-	-	-	-	-	0.14-0.22	≤0.045	≤0.050	-	Bal.
Stainless steel	-	≤1.0	≤2.0	-	-	-	18-20	8-10.5	≤0.08	≤0.035	≤0.03	-	Bal.
ER4043 filler	0.05	4.6-6.1	0.05	0.3	0.1	0.2	-	-	-	-	-	Bal.	0.8
ER5356 filler	5	0.3	0.15	0.05	0.05	0.1	0.1	-	-	-	-	Bal.	-

Fig. 1 Schematic diagram of bypass-current MIG welding-brazing experimental setup

Table 2 Welding parameters

Parameters	Al/galvanized steel	Al/stainless steel
Welding current of main circuit, I (A)	70	68
MIG torch argon gas flow, q₁ (L min^-1)	15	15
Bypass current, I (A)	55	30
BC torch argon gas flow, q₂ (L min^-1)	5	5
Welding voltage, U (V)	16.6	16
Welding speed, v (mm s^-1)	13.1	12
Distance between base metal and tungsten, h₁ (mm)	5	5
Distance between base metal and MIG torch, h₂ (mm)	12	10
Distance between MIG torch and tungsten, h₃ (mm)	5	3

Fig. 2 Seam appearance of the joints obtained by BC-MIG: a aluminum/galvanized steel joint, b aluminum/stainless steel joint

Fig. 3 Cross section of the joints obtained by BC-MIG: a aluminum/galvanized steel joint, b aluminum/stainless steel joint

Fig. 4 Interface macrographics of the joints: a aluminum/galvanized steel joint, b aluminum/stainless steel joint

Fig. 5 Flow of weld pool and droplet transfer with and without bypass current: a conventional MIG, b BC-MIG

Fig. 6 Arc shape and appearance of weld pool with and without bypass current: a conventional MIG, b BC-MIG

Fig. 7 Variation of currents with and without bypass current

Fig. 8 a Microstructure b line scanning analysis results of the aluminum/galvanized steel interfacial layer

Table 3 EDS results of the certain points indicated in Fig. 8a (at.%)

Point	Aluminum/galvanized steel
Point	Al	Si	Mg	Mn	Fe	Zn
A	96.33	2.22	1	0	0.45	0.67
B	81.82	12.74	0.7	0	4.51	0.23
C	69.65	11.33	1.3	0.32	17.39	0
D	64.56	8.92	1.15	0	25.36	0.54
E	20.53	2.79	1.87	0.25	74.56	0

Fig. 9 XRD analysis result of aluminum/galvanized steel reaction layer

Fig. 10 a Microstructure b line scanning analysis results of the aluminum/stainless steel interfacial layer

Table 4 EDS results of the certain points indicated in Fig. 10a

Point	Aluminum/stainless steel (at.%)
Point	Al	Si	Cr	Mn	Fe	Ni
A	100	0	0	0	0	0
B	73.91	0.63	3.99	0.71	19.93	0.83
C	70.63	1.38	4.46	0.49	22.67	0.37
D	43.22	1.7	11.13	1.43	35.93	6.58
E	4.55	2.94	18.95	1.89	62.46	9.21

Fig. 11 XRD analysis result of aluminum/stainless steel reaction layer

Fig. 12 Failure location of a aluminum/galvanized steel specimen, b aluminum/stainless steel specimen of the tensile strength testing

Fig. 13 Microhardness of the aluminum/galvanized steel joint (Hv)

Fig. 14 Microhardness of the aluminum/stainless steel joint (Hv)

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