Corrosion Resistance of Friction Stir Welded Al-Cu-Li Alloy AA2099-T8

doi:10.1007/s40195-019-00944-w

Abstract

Abstract:

In order to study the effect of friction stir welding (FSW) on corrosion resistance of Al-Cu-Li alloy AA2099-T8, the microstructure and microhardness of FSW joints were characterized, and then, the corrosion behavior of the FSW joints was investigated by the immersion and potentiodynamic polarization tests in a 3.5% NaCl solution at room temperature. It is indicated that the alloy was softened by FSW, with the lowest hardness appearing at the boundary between the nugget zone and the thermo-mechanically affected zone. When exposed to the NaCl solution, the FSW joint was characterized by shallow pits and was free of severe localized corrosion, probably due to dissolution of T₁ (A₂CuLi) phase in the FSW joint. It is suggested that further work should be carried out to evaluate the galvanic coupling effect between the FSW joint and the base metal, as well as the stress corrosion cracking resistance of the FSW joint.

Key words: Frictions stir welding (FSW), Al-Cu-Li alloy, AA2099, Localized corrosion

Yan-Long Ma, Hui-Bin Xu, Zhao-Yuan Liang, Lei Liu. Corrosion Resistance of Friction Stir Welded Al-Cu-Li Alloy AA2099-T8[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(1): 127-134.

Figures/Tables 10

Table 1 Chemical composition of AA2099-T8 alloy (wt%)

Elements	Cu	Li	Zn	Mg	Mn	Fe	Ti	Si	Zr	Al
Content	2.70	1.69	0.65	0.27	0.315	0.065	0.025	0.035	0.08	Balance

Fig. 1 Optical micrograph of the cross section of the friction stir welded AA2099-T8 aluminum alloy at low magnification. The boundaries between each of the regions are schematically indicated by the dashed lines

Fig. 2 Optical micrographs of the cross section of the friction stir welded AA2099-T8 aluminum alloy at increased magnification (retreating side): a HAZ; b TMAZ; c TMAZ/NZ; d NZ

Fig. 3 Microhardness of the welded joint measured from the half thickness of the plate

Fig. 4 Optical micrographs of the cross section of the friction stir welded AA2099-T8 aluminum alloy after immersion in 3.5% NaCl solution for 5 h: a NZ; b TMAZ; c HAZ; d BM

Fig. 5 Scanning electron micrographs of the cross section of the friction stir welded AA2099-T8 aluminum alloy after immersion in 3.5% NaCl solution for 5 h: a typical corrosion pits associated with IMPs; b continuous localized corrosion observed in the base metal

Fig. 6 Open circuit potentials of the BM and the NZ recorded during immersion in 3.5% NaCl solution

Fig. 7 Scanning electron micrographs of the top surfaces of the a NZ, b BM after immersion in 3.5% NaCl solution for 5 h

Fig. 8 Potentiodynamic polarization curves of the BM and the FSW NZ when potentiodynamically polarized from -?100 to 500 mV (OCP) at a scanning rate of 0.5 mV/s in 3.5 wt% NaCl solution

Fig. 9 Scanning electron micrographs of the top surfaces of the BM (a) and NZ (b) after polarization from -?100 to 500 mV (OCP) at a scanning rate of 0.5 mV/s in 3.5 wt% NaCl solution; c and d are the framed areas A and B at increased magnification

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