Microstructure and Mechanical Properties of Galvanized Steel/AA6061 Joints by Laser Fusion Brazing Welding

doi:10.1007/s40195-014-0091-x

Abstract

Abstract:

Laser fusion brazing welding was proposed. Galvanized steel/AA6061 lapped joint was obtained by laser fusion brazing welding technique using the laser-induced aluminium molten pool spreading and wetting the solid steel surface. Wide joint interface was formed using the rectangular laser beam coupled with the synchronous powder feeding. The result showed that the tiny structure with the composition of α-Al and Al–Si eutectic was formed in the weld close to the Al side. And close to the steel side, a layer of compact Fe–Al–Si intermetallics, including the Al-rich FeAl₃, Fe₂Al₅ phases and Al–Fe–Si τ1 phase, was generated with the thickness of about 10–20 μm. Transverse tensile shows the brittle-fractured characteristic along to the seam/steel interface with the maximum yield strength of 152.5 MPa due to the existence of hardening phases τ1 and Al–Fe intermetallics.

Key words: Galvanized steel, Aluminium alloy, Laser welding, Interface, Microstructural characterization, Mechanical property

Junxia Lü, Wuxiong Yang, Shikai Wu, Xudong Zhao, Rongshi Xiao. Microstructure and Mechanical Properties of Galvanized Steel/AA6061 Joints by Laser Fusion Brazing Welding[J]. Acta Metallurgica Sinica (English Letters), 2014, 27(4): 670-676.

Figures/Tables 11

Table 1 Mechanical properties of the base metals

Material	Tensile strength (MPa)	Yield strength (MPa)	Elongation (%)
AA6061-T6	280	230	8–15
Galvanized steel	395	350	35

Table 2 Chemical compositions of AA6061, low carbon steel, filler power, solder, and galvanized layer

Material	Si	Fe	Cu	Mn	Mg	Cr	Zn	Ti	Al
AA6061	0.52	0.5	0.18	0.09	0.84	0.22	0.16	0.13	Bal.
Filler powder	12	–	–	–	–	–	–	–	Bal.
BAl₈₈Si	12	–	–	–	–	–	–	–	Bal.

Material	C	Si	P	S	Mn	Fe	Ni	Zn	–
Carbon steel	0.08	0.03	0.025	0.02	0.40	Bal.	–	–	–
Galvanization	–	–	–	–	–	–	10–15	Bal.	–

Fig. 1 Schematic illustration of welding experimental setup: a side view; b front view; c diagram of the tensile test specimen

Fig. 2 a Energy distribution of the rectangular laser spot; b powder stream configuration of rectangular broadband nozzle

Fig. 3 Cross section of a galvanized steel/AA6061 joint showing the whole joint macromorphology a, microstructures of position A b, B c in a, the magnified image of zone E in c is shown in d (P = 2.0 kW, V = 0.12 m/min, Δf = +20 mm)

Table 3 Chemical elements content at different positions in weld (at%)

Position	Al	Mg	Si
1	93.86	0.78	4.61
2	94.1	0.69	5.21
3	93.86	–	6.14
4	85.67	–	14.33

Fig. 4 TEM images of the interfacial region in the galvanized steel-AA6061: aP = 4.0 kW, V = 0.12 m/min, Δf = +30 mm; bP = 3.0 kW, V = 0.3 m/min, Δf = +20 mm; cP = 2.0 kW, V = 0.12 m/min, Δf = +20 mm; d HRTEM of c

Fig. 5 Microhardness profile across the galvanized steel-AA6061 joint

Fig. 6 Macro-fracture image of the tensile-shear specimen for galvanized steel-AA6061 lapped joint: a macroscopic fractured morphology; b microsturctue of fractured section

Fig. 7 Cross section of the galvanized steel/aluminium interface: details of a compact structure below and the dendritic intermetallics in the upper part (P = 4.0 kW, V = 0.12 m/min, Δf = +20 mm)

Fig. 8 XRD patterns of galvanized steel/Al interface: a scan along to the lower surface of the compact structure; b scan along to the upper surface of the compact structure

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