Dendritic Boundary Corrosion of AA2198 Weld Using Fiber Laser Welding with Al-Cu Filler Wire

doi:10.1007/s40195-017-0698-9

Abstract

Abstract:

The microstructures and corrosion behaviors of AA2198-T851 alloy and weld were analyzed under corrosive conditions. Weld was formed using an innovative fiber laser welding process with AA2319 Al-Cu filler wire. The metallurgic morphology and distribution of the chemical compositions were determined using imaging techniques such as optical micrograph, scanning electron micrograph, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction. Corrosion was evaluated using an immersion test and electrochemical impedance spectroscopy in 3.5% NaCl solution at room temperature. Results indicate that the parent alloy suffered from pitting corrosion during the initial 4-h immersion which was caused by the inhomogeneous distribution of its chemical components and the different intermetallics formed during the rolling process. The weld experienced dendritic boundary corrosion under the same conditions due to the addition of the Al-Cu filler and rapid solidification during laser welding, which led to the precipitates Cu enrichment along the grain boundary. When a welding joint was immersed in the solution for 5 days, a big crack was observed across the center of the weld. In comparison, there was good corrosion resistance in the heat-affected zone with a compact protective film.

Key words: 2198 Aluminum alloy, Fiber laser welding, Dendritic boundary corrosion, Al-Cu filler wire

Jun-Xia Lu, Ling Chang, Shi-Kai Wu, Shi-Kun Yin. Dendritic Boundary Corrosion of AA2198 Weld Using Fiber Laser Welding with Al-Cu Filler Wire[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(7): 735-741.

Figures/Tables 11

Table 1 Chemical compositions of test materials (mass fraction %)

Alloy	Cu	Li	Mg	Mn	Zr	Ti	Fe	Si	Zn	Ag	Ni	Al
AA2198	3.24	0.99	0.33	< 1	0.11	0.03	0.04	0.03	0.01	0.29	< 1	Bal.
AA2319	6.0	-	0.21	0.29	0.19	0.06	0.3	0.2	0.1	-	-	Bal.

Fig. 1 Schematic illustration of the laser welding experimental setup

Fig. 2 Optical micrographs of a AA2198 parent alloy, b weld with AA2319 Al-Cu filler, c interface between weld and parent alloy

Fig. 3 XRD patterns of AA2198-T851 plate, weld and HAZ using fiber laser welding with Al-Cu filler wire

Fig. 4 TEM result of AA2198-T851 plate material showing a bright field structure; b SAED spot in bright area; c SAED spot in dark area

Fig. 5 EDS mapping of AA2198 weld, a SEM image, b element distribution, c Cu mapping, d Al mapping

Table 2 Element contents detected by EDS

	Al	Cu	Mg	Fe	Zn
Light zone	84.76	13.57	1.26	0.21	0.20
Dark zone	97.96	0.67	1.10	0.13	0.14

Fig. 6 a TEM image of the weld with AA2319 Al-Cu filler wire, b element spectrum in the grain boundary, c element spectrum in intracrystalline

Fig. 7 a Macrostructure of AA2198 joint after immersion in 3.5 wt% NaCl solution for 5 days, b enlarged view in the site A

Fig. 8 SEM images showing corrosion morphology of joint in 3.5 wt% NaCl solution: a parent alloy for 4 h, b weld for 4 h, the inset for 5 days, c HAZ for 4 h

Fig. 9 a EIS of AA2198 parent alloy and the weld after immersing in 3.5 wt% NaCl solution, b the partial magnification picture in a