Effect of Magnetic Field on Electrochemical Corrosion Behavior of H62 Brass Alloy

Abstract

This study investigates the influence of magnetic fields on the electrochemical corrosion behavior of aerospace-grade H62 brass alloy in 3.5 wt% NaCl solution and its underlying 10 mechanisms. Employing electrochemical testing techniques combined with surface characterization methods, we explored the effects of magnetic field intensity (25–100 mT) and orientation (parallel and perpendicular to electrode surface) on the corrosion kinetics and corrosion product evolution of H62 brass alloy. Results demonstrate that magnetic fields significantly accelerate the corrosion process of H62 brass alloy. Under parallel magnetic field (100 mT), the corrosion current density increased from 0.49 μA/cm² to 3.66 μA/cm², approximately 7.5 times that of the non-magnetic condition, while perpendicular magnetic field increased it to 1.73 μA/cm², approximately 3.5 times the baseline value. The charge transfer resistance decreased from 3382 Ω·cm² to 1335 Ω·cm². Magnetic field orientation determines the fundamental differences in corrosion acceleration mechanisms. Parallel magnetic fields primarily enhance mass transfer processes through Lorentz force-driven magnetohydrodynamic (MHD) effects, resulting in intensified uniform corrosion; perpendicular magnetic fields alter interfacial ion distribution through magnetic gradient forces, inducing localized corrosion tendencies. Magnetic fields promote the transformation of protective Cu₂O films into porous Cu₂(OH)₃Cl, reducing the protective capability of corrosion product layers.

1. Introduction

H62 brass alloy, as an important copper–zinc alloy material, is extensively utilized in aerospace applications including electrical connectors, conductive slip rings, heat exchangers, and hydraulic pipeline systems due to its excellent electrical conductivity, thermal conductivity, mechanical properties, and processability [1,2]. Modern aircraft contain numerous power electronic devices such as generators, transformers, electric actuators, and power distribution systems that generate complex electromagnetic field environments [3].

Particularly with the development of more-electric and all-electric aircraft technologies, the power ratings of onboard electrical equipment continue to increase, with magnetic field intensities inside aircraft reaching tens to hundreds of mT [4,5]. These persistent magnetic field environments may influence the corrosion behavior of copper alloy components, potentially threatening aircraft flight safety [6]. Therefore, investigating the influence of mechanisms of magnetic fields on aerospace H62 brass alloy corrosion behavior possesses significant theoretical and engineering value.

In recent years, the influence of magnetic fields on metal corrosion behavior has attracted extensive attention from researchers [7,8,9,10]. Wang et al. [7] systematically reviewed the corrosion mechanisms and research progress of metal pipelines under magnetic field and sulfate-reducing bacteria conditions, indicating that magnetic fields significantly affect corrosion processes through magnetohydrodynamic effects. Zhang et al. [8] investigated the effect of gradient magnetic fields on the corrosion of carbon steel pipes in seawater-pumped storage power plants, finding that magnetic fields perpendicular to the reaction surface promote corrosion, with more significant effects at higher magnetic field gradients. Zhao et al. [9] explored the effect of magnetic fields on the corrosion behavior of Fe83Ga17 alloy, confirming that parallel and perpendicular magnetic fields produce different corrosion effects through Lorentz force and magnetic gradient force, respectively. For copper alloys, Liu et al. [10] recently discovered that self-generated magnetic fields under current-carrying conditions accelerate atmospheric corrosion of copper conductors, promoting the transformation of Cu₂O to Cu₂(OH)₃Cl. However, systematic research on H62 brass in aerospace applications under magnetic field environments remains limited.

The mechanism of magnetic field influence on corrosion is primarily realized through magnetohydrodynamic (MHD) effects. In electrochemical corrosion systems, the main magnetohydrodynamic forces include paramagnetic force, Lorentz force, and magnetic gradient force [11]. Among these, the Lorentz force is considered the primary factor affecting corrosion processes. The direction and magnitude of the Lorentz force depend on the magnetic field direction and intensity. When the magnetic field is parallel to the electrode surface, the Lorentz force is perpendicular to the electrode surface, significantly affecting ion mass transfer processes [12].

Magnetic fields have complex effects on copper alloy corrosion in chloride media. They accelerate oxygen transport through MHD effects, enhancing cathodic depolarization [13]. Additionally, they influence chloride ion migration to electrode surfaces, which affects localized corrosion development [8]. Sherif et al. [14] found that in chloride-containing media, copper alloy surfaces form CuCl, Cu₂O, and other corrosion products, whose formation and transformation processes may be influenced by magnetic fields. Additionally, magnetic fields may affect the structure and protective properties of corrosion product films [15].

However, existing research on H62 brass alloy corrosion behavior under magnetic fields remains insufficient in the following aspects: (1) the mechanistic differences between parallel and perpendicular magnetic field orientations on corrosion kinetics have not been clarified; (2) systematic studies on the evolution of corrosion products under different magnetic field intensities and their effects on protective performance are lacking; and (3) the quantitative effects of Lorentz force and magnetic gradient force on corrosion processes in magnetic field environments have not been distinguished. Therefore, this study employs electrochemical testing techniques including potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS), combined with surface analysis methods including scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy, to systematically investigate the effects of magnetic field intensity (25–100 mT) and orientation (parallel and perpendicular to electrode surface) on the electrochemical corrosion behavior and corrosion product evolution of H62 brass in 3.5 wt% NaCl solution.

2. Materials and Methods

2.1. Electrochemical Experiments

The test material was H62 brass plate. According to the material quality certificate provided by AVIC Shenyang Xinghua Aviation Electric Appliance Co., Ltd. (Shenyang, Liaoning, China), the chemical composition was 61.56 wt% Cu, 38.43 wt% Zn, and 0.006 wt% Pb, which conforms to the H62 brass composition requirements in GB/T 5231-2012 standard [16]. Specimens were machined into 10 mm × 10 mm × 1.5 mm dimensions. Copper wire was soldered to one end of the specimen, non-working surfaces were sealed with epoxy resin, and working surfaces were progressively polished with 400#, 800#, 1200#, 1600#, 2000# sandpaper to mirror finish, followed by degreasing and cleaning.

Electrochemical measurements were performed using a PARSTAT 4000A electrochemical workstation with a three-electrode system (working electrode: H62 brass; reference electrode: saturated calomel electrode (SCE); counter electrode: platinum sheet). The test solution was 3.5 wt% NaCl (pH = 6.95). All electrochemical tests were conducted at room temperature (25 ± 1 °C). Before testing, specimens were immersed in the test solution for 30 min to reach a stable open-circuit potential (OCP).

Potentiodynamic polarization curves were scanned at OCP ± 250 mV with a scan rate of 0.167 mV/s. The Tafel regions of the polarization curves were fitted using Cview software through Tafel extrapolation method to obtain the corrosion potential and corrosion current density, thereby quantitatively evaluating the effect of magnetic field on the corrosion rate of H62 brass.

Electrochemical impedance spectroscopy (EIS) was conducted with a frequency range of 0.01 Hz to 1 MHz and perturbation amplitude of ± 10 mV. EIS data were fitted using Zview3 software with equivalent circuit models to obtain interfacial electrochemical parameters, thereby revealing the mechanisms of magnetic field effects on the electrode/solution interface structure and charge transfer process of H62 brass.

Each experiment was repeated three times to ensure data reliability. All electrochemical curves were plotted using Origin2025 software.

Magnetic fields were generated by neodymium–iron–boron permanent magnets positioned on both sides of the electrochemical cell. By adjusting magnet spacing and quantity, magnetic field intensities of 0, 25, 50, 75, and 100 mT were achieved, calibrated using a TD8620 digital teslameter. Parallel and perpendicular magnetic field orientations were obtained by changing the relative direction between the magnets and the working electrode, as shown in Figure 1. The three-electrode system remained in a fixed position throughout all experiments, with only the magnet positions being adjusted to achieve different magnetic field orientations.

2.2. Surface Characterization and Composition Analysis

After 7-day immersion under corresponding magnetic field conditions, corrosion morphology was observed using SEM3200 scanning(CIQTEK, Hefei, China) electron microscopy in secondary electron (SE) mode at an accelerating voltage of 20 kV, with integrated energy dispersive spectroscopy (EDS) for elemental composition analysis. Corrosion product phase composition was analyzed by identifying characteristic peaks using Horiba LabRAM HR Evolution Raman spectroscopy (532 nm laser, 10% power, 50× objective).

3. Results

3.1. Electrochemical Analysis

3.1.1. Potentiodynamic Polarization Curve Analysis

Potentiodynamic polarization curve test results indicate that magnetic fields significantly influence the electrochemical corrosion behavior of H62 brass alloy. Figure 2 shows potentiodynamic polarization curves of H62 brass under different magnetic field conditions. With increasing magnetic field intensity, both cathodic and anodic polarization curves shift toward higher current density regions under different field orientations, indicating that magnetic fields decrease corrosion potential and increase corrosion current density, reducing the corrosion resistance of H62 brass. Tafel region analysis of potentiodynamic polarization curves reveals that magnetic fields primarily affect cathodic reaction kinetics. Under non-magnetic conditions, cathodic reactions are oxygen diffusion-controlled; with applied magnetic fields, dissolved oxygen mass transfer rates increase and cathodic Tafel slopes decrease, indicating cathodic reactions transition from diffusion control to mixed control [17].

Fitting with Cview3.5 software yielded corrosion current and corrosion current density under different magnetic field intensities, as shown in

Table 1. Fitted corrosion potential, corrosion current density, Tafel slopes, and corrosion rates under different magnetic fields.

B (mT)		Ecorr (mV)	Icorr (μA/cm2)	βc (mV/dec)	βa (mV/dec)	CR (mm/Year)
0		−223.21	0.49	36.41	11.44	0.060
Parallel	25	−231.64	1.06	57.96	15.15	0.130
Perpendicular	50	−238.82	1.60	63.46	13.40	0.196
	75	−236.51	2.78	83.03	24.26	0.341
	100	−238.37	3.66	78.55	13.68	0.449
	25	−230.20	0.83	49.65	10.64	0.102
	50	−244.86	1.21	74.86	33.72	0.148
	75	−263.47	1.66	63.00	20.51	0.204
	100	−270.96	1.73	53.40	28.18	0.212

. With increasing magnetic field intensity, under parallel magnetic field, H62 brass corrosion potential negatively shifted approximately 15 mV, and corrosion current density increased approximately 7.5-fold; under perpendicular magnetic field, corrosion potential negatively shifted approximately 48 mV, and corrosion current density increased approximately 3.5-fold. Magnetic field orientation also significantly influenced the Tafel slopes. Under parallel magnetic field (100 mT), the cathodic Tafel slope βc increased from 36.41 mV/dec to 78.55 mV/dec, while under perpendicular magnetic field it increased to 53.40 mV/dec. In contrast, the anodic Tafel slope βa remained relatively stable under both field orientations.

Corrosion rates (CR) calculated from Icorr using Faraday’s law are also listed in Table 1, showing proportional trends with corrosion current densities.

According to studies by Waskaas and Kharkats [18,19], when the magnetic field is parallel to the electrode surface, current density is perpendicular to the magnetic field direction, Lorentz force reaches maximum value, generating strong magnetohydrodynamic (MHD) convection at the electrode surface, significantly enhancing mass transfer processes. This convection reduces diffusion boundary layer thickness, substantially increasing transport rates of corrosive species such as chloride ions to the electrode surface, leading to marked increases in corrosion current density. However, since this primarily affects mass transfer-controlled cathodic reactions with relatively minor effects on charge transfer kinetics, corrosion potential shifts only 15 mV negatively.

Under perpendicular magnetic field conditions, when current density is parallel to the magnetic field direction, Lorentz force equals zero, unable to generate significant bulk convection enhancement. However, perpendicular magnetic fields create non-uniform magnetic field distributions at electrode surfaces, generating magnetic gradient forces. These forces act on paramagnetic ions (such as O₂) and dissolved Zn²⁺ and Cu²⁺ ions from the copper alloy, causing uneven ion concentration distribution at the electrode/solution interface [20]. Perpendicular magnetic fields also affect double layer structure, compressing the diffusion layer and altering interfacial charge distribution, leading to relative changes in anodic and cathodic reaction kinetics, producing greater corrosion potential negative shifts than parallel magnetic fields.

3.1.2. EIS Analysis

While increasing magnetic field intensity accelerates H62 brass corrosion, different magnetic field orientations exhibit significantly different action mechanisms. To elucidate specific principles, Nyquist and Bode plots showing H62 brass impedance spectrum variations under different magnetic fields were obtained through Zview fitting, as shown in Figure 3.

From Nyquist plots, electrochemical impedance characteristic curves under different magnetic intensities approximate a single continuous capacitive arc, without obvious Warburg impedance lines or second capacitive arcs, indicating that under applied magnetic fields, H62 brass impedance spectra feature single capacitive arcs as the core characteristic. This is because the rate-determining step for H62 brass working electrodes is the electrochemical charge transfer process, i.e., electrochemical activation control. The capacitive arc radius reflects charge transfer resistance magnitude. Smaller capacitive arc radii correspond to lower charge transfer resistance, higher electrochemical reaction rates, and poorer H62 brass corrosion resistance. Capacitive arc radius is at maximum without magnetic field and decreases significantly with increasing magnetic intensity for both parallel and perpendicular fields.

H62 brass Bode plots exhibit typical capacitive impedance characteristics: impedance modulus decreases monotonically with increasing frequency, with consistent slopes in mid-high frequency ranges, reflecting coupling between double layer capacitance and charge transfer resistance; phase angle shows only a single mid-frequency peak without low-frequency plateau, demonstrating corrosion processes are charge transfer-controlled, with mass transfer not the primary limiting step. Increasing magnetic field intensity causes synchronous decreases in impedance modulus and phase angle, indicating magnetic fields accelerate corrosion processes by weakening interfacial passivation film stability and reducing charge transfer resistance. Phase angle peak changes are smaller under parallel magnetic fields, while perpendicular magnetic fields show significant phase angle peak decreases, indicating perpendicular magnetic fields more significantly affect interfacial capacitive characteristics.

To further investigate magnetic field effects on H62 brass electrochemical impedance in 3.5 wt% NaCl solution, considering the three-layer “solution-product film-electrode substrate” corrosion interface structure, the equivalent circuit model shown in Figure 4 was used to fit H62 brass EIS data. Equivalent elements include solution resistance R_s, corrosion product film resistance R_f, product film constant phase element CPE_f, charge transfer resistance R_ct, and interfacial double layer constant phase element CPE_dl. Fitting results are shown in

Table 2. Equivalent circuit fitting parameters under different magnetic fields.

B (mT)		Rs (Ω·cm2)	Cf (μF·cm−2)	nf	Rf (Ω·cm2)	Cdl (μF·cm−2)	ndl	Rct (Ω·cm2)
0		5.34	4.046	0.964	18.63	64.9	0.645	3382
Parallel	25	5.032	4.706	0.885	7.103	74.18	0.641	2992
Perpendicular	50	4.094	5.15	0.857	14.18	115.5	0.615	1796
	75	3.278	8.754	0.961	31.96	76.95	0.664	1377
	100	7.601	17.58	0.925	27.04	119.7	0.538	1396
	25	10.41	4.778	0.834	10.89	69.26	0.637	2726
	50	8.972	4.875	0.964	4.778	93.75	0.581	2454
	75	2.402	7.363	0.834	11.08	234.5	0.545	1370
	100	9.8	22.18	0.891	20.44	176	0.541	1335

. Fitting parameters include C_f and n_f corresponding to capacitance conversion value and dispersion coefficient of CPE_f, respectively, and C_dl and n_dl corresponding to capacitance conversion value and dispersion coefficient of CPE_dl, respectively. Due to surface roughness and non-uniform product film adsorption at actual corrosion interfaces, ideal capacitors cannot accurately describe interface characteristics, thus constant phase elements (CPE) are employed; when 0.5 < n < 1, CPE effectively characterizes non-ideal interface capacitive behavior, better conforming to actual corrosion scenarios.

R_ct characterizes charge transfer resistance at the H62 brass/solution interface, its value inversely proportional to corrosion rate, serving as the key parameter reflecting magnetic field effects on corrosion kinetics. Table data shows all R_ct values under magnetic field conditions are lower than non-magnetic R_ct (3382 Ω·cm²), indicating magnetic fields accelerate corrosion reactions by reducing charge transfer resistance. The R_ct decrease primarily results from magnetic field-enhanced mass transfer processes increasing reactant concentrations at electrode surfaces, particularly increased dissolved oxygen and chloride ion concentrations accelerating cathodic and anodic reactions. Under perpendicular magnetic field conditions, although mass transfer enhancement is limited, magnetic gradient forces alter interfacial ion distribution, similarly causing R_ct reduction.

Product film resistance R_f variations reflect magnetic field effects on corrosion product layer formation and stability. Under parallel magnetic fields, R_f shows an initial increase then decrease with magnetic field intensity, reaching maximum 31.96 Ω·cm² at 75 mT, slightly decreasing to 27.04 Ω·cm² at 100 mT; under perpendicular magnetic fields, R_f is overall lower than parallel fields, with maximum 20.44 Ω·cm², indicating parallel magnetic fields show more significant enhancement of product film protective properties at equivalent magnetic field intensities. This suggests magnetic gradient forces under perpendicular fields may directly disrupt product film compactness, facilitating chloride ion penetration [21].

Double layer capacitance C_dl shows marked differences depending on magnetic field orientation, directly reflecting magnetic field effects on H62 brass interfacial charge distribution. At 100 mT, perpendicular field C_dl increases from 64.9 μF·cm⁻² without field to 176.0 μF·cm⁻², far exceeding 119.7 μF·cm⁻² under 100 mT parallel field. This occurs because parallel field-induced convection compresses diffusion layer thickness increasing interfacial charge density, while perpendicular fields cause double layer distortion through gradient forces, enhancing surface non-uniformity [22]. This corresponds with Bode plots showing lower phase angle peaks under perpendicular fields, further demonstrating differentiated characteristics of magnetic field orientation effects on H62 brass interfacial state modulation.

3.2. Characterization

3.2.1. Low-Magnification SEM Corrosion Morphology and EDS Analysis

Figure 5, Figure 6 and Figure 7 show low-magnification SEM corrosion morphology (×90) of H62 brass after 7-day immersion under different magnetic field conditions, with representative EDS spectra presented in Figure 8.

Under non-magnetic conditions (Figure 5), specimen surfaces show relatively sparse corrosion product distribution, with products in fine granular form, relatively smooth surface morphology, and good corrosion product layer compactness.

Under parallel magnetic field action (Figure 6), H62 brass corrosion product density markedly increases compared to non-magnetic conditions, with corrosion products uniformly distributed in granular form. With increasing magnetic field intensity, corrosion products further increase and show aggregation phenomena, surface roughness increases, and higher magnetic field intensities form extensive loose porous corrosion product layers with obvious product spalling in some regions.

Under perpendicular magnetic field conditions (Figure 7), corrosion product distribution differs significantly from parallel fields. Perpendicular field corrosion product distribution is relatively non-uniform, showing localized corrosion tendencies. For example, at 50 mT, some regions show dark corrosion pits while other regions remain relatively intact; at 75 mT, surfaces form obvious “hill-like” non-uniform corrosion morphology with island-distributed corrosion products; at 100 mT, localized corrosion is extremely severe with deep pits and cracks, though overall corrosion degree is lower than equivalent intensity parallel fields.

Figure 8 shows representative EDS spectra of corrosion products under different magnetic field conditions. The spectra confirm the presence of Cu, Zn, O, and Cl elements in all samples, and the relative intensities of these elemental peaks vary with magnetic field conditions, indicating compositional differences in the corrosion product layers.

Table 3. EDS analysis results of H62 brass corrosion products under different magnetic fields (atomic %).

B (mT)		Cu	Zn	O	Cl
0		38.42	31.08	29.83	0.67
Parallel	25	13.65	29.22	52.56	4.57
Perpendicular	50	9.24	25.85	59.33	5.58
	75	8.38	22.39	63.32	5.91
	100	7.79	18.79	67.20	6.22
	25	29.17	26.30	42.83	1.70
	50	23.90	20.27	53.02	2.81
	75	27.17	10.87	60.04	1.92
	100	13.58	22.23	62.26	1.93

presents the complete quantitative elemental composition data obtained from EDS analysis under all magnetic field conditions.

Under non-magnetic conditions, corrosion product elemental composition is relatively balanced. With increasing magnetic field intensity, corrosion product elemental composition changes significantly. Under parallel magnetic field conditions, O element content indicates enhanced corrosion product oxidation degree. Under perpendicular magnetic field conditions, although O element content also consistently increases, its variation level remains consistently lower than parallel fields, indicating specimens oxidize more readily under parallel fields. Cl element content in corrosion products under parallel fields also increases with magnetic field intensity and is significantly higher than perpendicular fields. High Cl content corrosion product layers have loose structures with significantly reduced protective performance, resulting in more severe corrosion [23].

3.2.2. High-Magnification SEM Corrosion Morphology and Raman Spectroscopy Analysis

For further clarification of corrosion product composition, Raman spectroscopy analysis was performed on the corrosion products. As shown in Figure 9, H62 brass corrosion products in 3.5 wt% NaCl solution mainly consist of Cu₂O (218 cm⁻¹) and Cu₂(OH)₃Cl (815 cm⁻¹), with relative contents varying significantly with magnetic field conditions [24,25]. The significant Raman peak at 2020 cm⁻¹ is a composite peak formed by superposition of Cu₂O lattice vibration higher-order harmonic peaks, Cu₂(OH)₃Cl vibration combination frequency peaks, and weak O–H bond vibration peaks [26]; the broad Raman peak at 3050 cm⁻¹ under 100 mT parallel field (Figure 9a) represents O–H bond stretching vibration peaks from surface-adsorbed water or hydroxyl groups in corrosion products.

Figure 10 shows high-magnification SEM morphology (×900) under non-magnetic and 100 mT parallel and perpendicular magnetic fields. Under non-magnetic conditions, high-magnification SEM shows relatively smooth corrosion product surfaces with dense Cu₂O distribution and only small amounts of Cu₂(OH)₃Cl particles scattered on top. Parallel magnetic fields show obvious lamellar Cu₂(OH)₃Cl structures [27]. Under perpendicular magnetic field conditions, Cu₂(OH)₃Cl presents spherical particle aggregation morphology with non-uniform distribution, with Cu₂O substrate still visible in localized regions.

This corresponds with Raman spectroscopy results shown in Figure 9a, where continuous decrease in Cu₂O characteristic peak intensity and gradual increase in Cu₂(OH)₃Cl peak intensity under parallel fields, with protective Cu₂O film gradually transforming to loose porous Cu₂(OH)₃Cl. In comparison, perpendicular fields also cause Cu₂O to Cu₂(OH)₃Cl transformation, but Raman peaks in Figure 9b show asymmetric and irregular intensity variations, related to perpendicular field-induced interfacial distortion promoting localized corrosion rather than overall mass transfer enhancement accelerating corrosion like parallel fields. These differences are fully demonstrated in the composition, distribution, and evolution characteristics of corrosion products.

4. Discussion

Based on the above electrochemical testing results, the corrosion mechanism of H62 brass in 3.5 wt% NaCl solution can be clearly elucidated. Potentiodynamic polarization curve analysis (Section 3.1.1) demonstrates that magnetic fields significantly accelerate the corrosion process by altering the rate-controlling step of the cathodic oxygen reduction reaction (transitioning from diffusion control to mixed control) and promoting anodic metal dissolution reactions. Electrochemical impedance spectroscopy analysis (Section 3.1.2) further reveals the mechanisms by which magnetic fields reduce charge transfer resistance, modify corrosion product film properties, and enhance interfacial capacitive characteristics. The differences in magnetic field orientation lead to distinct mechanical driving mechanisms: parallel magnetic fields primarily enhance mass transfer processes through Lorentz forces, while perpendicular magnetic fields alter interfacial ion distribution through magnetic gradient forces.

To gain deeper insight into the chemical reaction processes underlying these electrochemical phenomena, the corrosion of H62 brass in chloride-containing media involves the following reaction equations:

Odic reactions [28]:

$$\mathrm{Cu}\to {\mathrm{Cu}}^{+}+{\mathrm{e}}^{-}$$

(1)

$${\mathrm{Cu}}^{+}\to {\mathrm{Cu}}^{2+}+{\mathrm{e}}^{-}$$

(2)

$$\mathrm{Zn}\to {\mathrm{Zn}}^{2+}+2{\mathrm{e}}^{-}$$

(3)

Complexation reactions [29]:

$${\mathrm{Cu}}^{+}+{\mathrm{Cl}}^{-}\to {\mathrm{CuCl}}_{(\mathrm{ad})}$$

(4)

$${\mathrm{CuCl}}_{(\mathrm{ad})}+{\mathrm{Cl}}^{-}\to {\mathrm{CuCl}}_2^{-}$$

(5)

Corrosion product formation [24,25]:

$$2{\mathrm{CuCl}}_2^{+}+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{Cu}}_2\mathrm{O}+4{\mathrm{Cl}}^{-}+2{\mathrm{H}}^{+}$$

(6)

$${\mathrm{Cu}}_2\mathrm{O}+3{\mathrm{H}}_2\mathrm{O}+2{\mathrm{Cl}}^{-}\to {\mathrm{Cu}}_2{(\mathrm{OH})}_3\mathrm{Cl}+{\mathrm{OH}}^{-}+2{\mathrm{H}}^{+}$$

(7)

Cathodic reaction [17]:

$${\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{O}+4{\mathrm{e}}^{-}\to 4{\mathrm{OH}}^{-}$$

(8)

The influence of magnetic fields on metal electrochemical corrosion is primarily realized through magnetohydrodynamic effects such as Lorentz force and magnetic gradient force [9]. The Lorentz force density expression is:

$$F_L=J\times B$$

(9)

where F_L is Lorentz force density (N/m³), J is current density vector (A/m²), and B is magnetic flux density vector (T). The Lorentz force direction is perpendicular to the plane formed by current density and magnetic field directions, with magnitude depending on their angle. When magnetic field direction is perpendicular to current density, Lorentz force reaches maximum; when parallel, Lorentz force equals zero.

Under parallel magnetic field conditions, Lorentz force-driven MHD convection significantly alters reactant and product transport processes [11]. The Lorentz force acts on metal ions produced by Equations (1)–(3) as they leave the electrode surface, altering their trajectories and increasing their residence time at the interface [12]. This retention effect promotes complexation reactions (4) and (5). Experimental results show Cl content in corrosion products reaches 6.22% under 100 mT parallel field, far exceeding 0.67% without field, confirming significantly enhanced Cl⁻ transport to interfaces. This finding is consistent with previous studies showing that magnetic fields enhance aggressive ion transport in corrosion systems [7]. High Cl⁻ concentration shifts reaction (6) equilibrium leftward, inhibiting protective Cu₂O formation while promoting Cu₂O to loose Cu₂(OH)₃Cl transformation in reaction (7). Raman spectroscopy observations of weakened Cu₂O peak (218 cm⁻¹) and enhanced Cu₂(OH)₃Cl peak (815 cm⁻¹) verify this phase transformation process.

Under perpendicular magnetic field conditions, since current density is parallel to magnetic field direction, Lorentz force equals zero, unable to generate significant bulk convection. However, perpendicular magnetic fields influence corrosion processes through magnetic gradient force [9]:

$$F_{\nabla B}={\chi }_{M}c{\displaystyle \frac{B\nabla B}{{\mu }_0}}$$

(10)

where $F_{\nabla B}$ is magnetic gradient force, ${\chi }_M$ is molar magnetic susceptibility, c is particle concentration, B is magnetic flux density, $\nabla B$ is magnetic flux density gradient, and ${\mu }_0$ is vacuum permeability. Under perpendicular fields, magnetic field gradients at electrode edges cause selective ion migration and enrichment [30]. Paramagnetic species (O₂ molecules and Cu²⁺ ions) are attracted to high magnetic field intensity regions, while diamagnetic species (Cl⁻) are repelled to low field regions [20]. This magnetic separation of ionic species has been observed in various electrochemical systems [31]. Locally high Cu²⁺ and O₂ concentrations promote localized corrosion reactions, while non-uniform Cl⁻ distribution causes localized differences in corrosion products. EDS analysis shows Cl content under perpendicular fields (1.70–2.81%) is lower than parallel fields but more non-uniformly distributed. SEM-observed “hill-like” corrosion morphology corresponds with this local concentration modulation mechanism. Perpendicular field corrosion current density increases 3.5-fold, lower than parallel fields, but corrosion potential negative shift is greater, indicating more significant effects on interfacial electrochemical states.

It should be noted that some studies have reported that magnetic fields can provide corrosion protection for certain metals by enhancing passive film formation or inhibitor adsorption. However, in aggressive chloride environments without inhibitors, as demonstrated in this study, magnetic field-enhanced mass transfer accelerates the delivery of corrosive species (Cl⁻, O₂) to the electrode surface, thereby accelerating corrosion. The effect of magnetic fields on corrosion depends on material properties (ferromagnetic vs. non-ferromagnetic), solution chemistry (presence of inhibitors or passivating agents), and magnetic field parameters, which explains the apparently contradictory observations in the literature.

5. Conclusions

(1)

Potentiodynamic polarization tests demonstrate that magnetic fields significantly accelerate H62 brass corrosion. Under 100 mT parallel magnetic field, corrosion current density increases from 0.49 μA/cm² to 3.66 μA/cm² (7.5-fold increase); under perpendicular magnetic field, it increases to 1.73 μA/cm² (3.5-fold increase).

(2)

Electrochemical impedance spectroscopy analysis reveals that magnetic fields accelerate corrosion kinetics by reducing charge transfer resistance (from 3382 Ω·cm² to 1335 Ω·cm²) and increasing double layer capacitance (from 64.9 μF·cm⁻² to 176.0 μF·cm⁻²).

(3)

SEM and EDS analysis show that parallel magnetic fields promote uniform corrosion product distribution with Cl content reaching 6.22%; perpendicular magnetic fields result in “hill-like” non-uniform corrosion morphology with localized corrosion tendencies and lower Cl content (1.93%) but non-uniform distribution.

(4)

Raman spectroscopy confirms that magnetic fields promote the transformation of protective Cu₂O films into porous Cu₂(OH)₃Cl, reducing the protective capability of corrosion product layers. Under parallel magnetic field, the Cu₂(OH)₃Cl characteristic peak (815 cm⁻¹) intensity significantly increases while the Cu₂O characteristic peak (218 cm⁻¹) weakens.

(5)

Magnetic field orientation determines fundamental differences in corrosion acceleration mechanisms: parallel magnetic fields enhance mass transfer processes through Lorentz force-driven magnetohydrodynamic effects, resulting in intensified uniform corrosion; perpendicular magnetic fields alter interfacial ion distribution through magnetic gradient forces, inducing localized corrosion tendencies.

While this study provides fundamental insights into magnetic field effects on H62 brass electrochemical corrosion mechanisms, several limitations should be acknowledged. The experiments were conducted under static magnetic field conditions in 3.5 wt% NaCl solution with field intensities of 25–100 mT. Future research should investigate broader environmental conditions (acidic, alkaline solutions), higher magnetic field intensities, dynamic or alternating fields, long-term corrosion behavior, and comparative studies on different copper alloys to comprehensively understand magnetic field effects on metallic corrosion.