posted on 2023-11-30, 13:07authored byZhaogui Lai, Feifei Huang, Lei Wen, Zhaoyang Zhao, Ying Jin
The corrosion behavior of the dissimilar metal welded
joint (DMWJ)
is highly dependent on its heterogeneous microstructures. However,
directly measuring the electrochemical properties of microstructures
in different heat-affected zones (HAZs) is a formidable challenge,
because traditional bulk electrochemistry can only offer an average
signal. Herein, the microelectrochemical properties of an SA508–309L/308L DMWJ were measured in 3.5 wt % NaCl solution using
lithography and capillary techniques. Specifically, high-throughput
microelectrochemical tests, including open circuit potential (OCP),
electrochemical impedance spectroscopy (EIS), and potentiodynamic
polarization (PDP), were conducted on 168 spots (Φ 12 μm).
Results revealed five typical EIS responses and seven varieties of
PDP curves (different magnitudes of the current density). The maps
of thermodynamic and kinetic metrics, such as polarization resistance
derived from EIS, corrosion potentials, and corrosion currents extracted
from potentiodynamic polarization curves, demonstrated good consistency.
The uniform corrosion tendency of the SA508 HAZ subregions during
the immersion tests is basically consistent with its Ecorr_avg order of subcritical HAZ (C5, −371 mV)
< intercritical HAZ (C4, −546 mV) < fine-grained HAZ2
(C3, −579 mV) < fine-grained HAZ1 (C2, −593 mV).
The random presence of inclusions leads to highly heterogeneous microelectrochemical
properties of the DMWJ, thereby causing localized corrosion to occur
preferentially. Moreover, the macroscopic corrosion behavior is affected
by the corrosion products, which display a protective effect that
modifies the local electrochemical activity of the SA508 HAZ. The
combination of microelectrochemical properties allows for a more comprehensive
understanding of the macroscopic corrosion behavior of metals and
the galvanic effect between the heterogeneous microstructures.