Effects of Cl⁻ and Acetic Acid Contents on the Corrosion Behavior of Al in SWAAT Environment

Abstract

This study quantitatively investigates the corrosion behavior of aluminum (Al1070) under salt water acetic acid test (SWAAT) conditions, focusing on the effects of chloride ions (Cl⁻) and acetic acid (CH₃COOH) concentration on the pitting corrosion. Potentiodynamic polarization tests showed that increasing Cl⁻ concentration caused a negative shift in corrosion potential (E_corr) and an increase in corrosion current density (i_corr), indicating accelerated passive film breakdown and enhanced pitting susceptibility. Immersion tests and SEM analysis revealed intensified surface discoloration, oxide formation, and crack propagation at higher Cl⁻ levels, confirming localized dissolution. The effect of acetic acid was evaluated for concentrations ranging from 0 to 2000 µL L⁻¹. Higher acetic acid levels lowered solution pH and slightly increased E_corr and elevated i_corr while reducing ΔE(E_pit − E_corr), indicating increased localized corrosion susceptibility. SEM and 3D XCT analyses showed increased pit density, corrosion loss, and pitting showed temporary pit coalescence at intermediate concentrations. Mechanistically, the acidic SWAAT environment (pH 2.8–3.0) positions aluminum in the active corrosion region. Cl⁻ destabilizes the passive oxide layer, initiating pitting, while acetic acid promotes metal dissolution via hydrogen evolution reactions. Their combined action exerts a specific effect, accelerating localized corrosion through chemical oxide layer degradation. These results provide quantitative insights into aluminum corrosion under SWAAT conditions. They could inform the design of corrosion resistant materials and reliability assessments in industrial applications.

1. Introduction

Aluminum alloys have been extensively used in heat exchangers due to their excellent thermal conductivity (235 W m⁻¹ K⁻¹), light weight (2.70 g cm⁻³) and formability, making them ideal materials for applications such as refrigerator and air conditioning systems [1,2,3,4]. Their general corrosion resistance stems from the spontaneous formation of a thin, stable and adherent oxide film, which passivates the surface and inhibits further dissolution in neutral or mildly alkaline environments [5,6]. However, this passive film is not entirely stable under aggressive environmental conditions. In the presence of chloride ions, high humidity, or moisture condensation, the passive layer can locally degrade, initiating localized corrosion such as pitting and intergranular attack [7,8,9]. These effects are further exacerbated in confined geometries—such as crevices between fins or tube joints. Electrolyte stagnation in areas promotes the accumulation of corrosive species, potentially leading to material perforation and leakage in heat exchanger components [10,11,12]. To evaluate the corrosion performance of aluminum alloys under such harsh conditions, several accelerated test methods are being utilized. The neutral salt spray test, which utilizes a continuous spray of 5 wt.% NaCl at 35 °C, is widely applied for assessing atmospheric corrosion resistance [13]. The cyclic corrosion test (CCT), involving alternating cycles of salt spray, humidity and drying at 25–50 °C, provides a closer approximation of real outdoor exposure. Among these, the seawater acidified accelerated test (SWAAT) represents one of the most aggressive testing environments [14], employing acidified seawater (pH 2.8–3.0) at 49 °C under cyclic wet/dry conditions [15,16,17]. Previous studies on aluminum corrosion under SWAAT conditions have primarily focused on the degradation behavior of anodized layers, conversion coatings and base alloys under highly accelerated exposure. Zhang et al. reported significant pit formation and passive film breakdown in anodized aluminum exposed to SWAAT [18,19,20,21]. El-Shamy demonstrated increased corrosion rates of AA2024 in acidified synthetic seawater [22,23], while Fushimi et al. investigated the effect of acetate ions on passive film breakdown using electrochemical impedance spectroscopy, highlighting film destabilization mechanisms in acidic chloride-containing solutions [24]. Nevertheless, most prior investigations have considered the SWAAT environment as a fixed standard, evaluating the effect of chloride ions or acetic acid independently. The combined effects of these two constituents—both of which are critical to passive film destabilization and metal ion solubilization—have not been systematically investigated [25,26,27,28,29,30,31,32]. Despite their importance in the initiation and propagation of pitting corrosion, few studies have directly addressed how their interaction influences the long-term corrosion behavior of aluminum alloys in SWAAT environments [33,34,35,36].

In this study, the corrosion behavior of aluminum alloys was quantitatively investigated under SWAAT conditions in which the concentrations of chloride ions and acetic acid were varied. The objective was to elucidate the individual and combined effects of these species on pitting corrosion initiation and propagation. Electrochemical techniques and surface characterization were employed to clarify their roles in the corrosion mechanism. The results are expected to contribute to a more mechanistic understanding of aluminum corrosion in acidified marine environments and support the development of more corrosion-resistant aluminum materials for heat exchanger applications.

2. Materials and Methods

2.1. Sample Preparation

Commercially pure aluminum (Al1070) hollow tube specimens were used in this study. The specimens were cut to a length of 30 mm with an outer diameter of 10 mm. To accurately define the exposed area, the cut ends and non-exposed regions were masked prior to corrosion testing. The effective exposed surface area was calculated as 6.28 cm² and consistently applied for all corrosion rate calculations and comparative analyses. Before testing, all specimens were ultrasonically cleaned in ethanol for 10 min and then dried in an oven at 40 °C. High-purity ethanol (≥99.7 wt.%, Daejung Chemicals & Metals Co., Ltd., Siheung, Republic of Korea) was used for all cleaning procedures.

2.2. SWAAT Immersion Test

The SWAAT test solutions were prepared using high-purity NaCl (CAS No. 7647-14-5, Daejung Chemicals & Metals Co., Ltd., Siheung, Republic of Korea), acetic acid (CH₃COOH, ≥99.7%, CAS No. 64-19-7, Daejung Chemicals & Metals Co., Ltd., Republic of Korea) and deionized water. The solution pH was adjusted to 2.8–3.0 by adding acetic acid, with a fixed addition of 300 μL L⁻¹ applied to all test conditions to reproduce SWAAT environments. Immersion tests were conducted at 50 °C under two controlled conditions. To study effects of NaCl concentrations (0–10 wt.%) on the corrosion behavior of aluminum, immersion test was conducted for 120 h in SWAAT solution. To evaluate the effect of acetic acid concentration, the NaCl concentration was fixed at 5 wt.% and specimens were immersed for 96 h. This immersion duration was identified as the minimum time necessary to clearly distinguish differences in corrosion characterization and pit growth behavior. After immersion, all specimens were rinsed with distilled water, ultrasonically cleaned in ethanol for 10 min to remove corrosion products and dried at room temperature.

2.3. Electrochemical Measurements

Electrochemical polarization experiments were carried out using a conventional three-electrode cell configuration. An Al1070 specimen was employed as the working electrode (WE), a saturated calomel electrode (SCE) as the reference electrode (RE) and a Pt (99.9%) sheet as the counter electrode (CE). Prior to each polarization measurement, the open circuit potential (OCP) of the working electrode was monitored until a stable state was achieved rather than for a fixed duration. OCP stabilization was defined as a potential fluctuation within ±2 mV over 300 s, which typically required approximately 1 h under the present experimental conditions. All polarization experiments were conducted at 50 °C in a 5 wt.% NaCl solution containing acetic acid, with the pH adjusted to 2.8–3.0. Open circuit potential and polarization behavior were measured using a PARSTAT 300 electrochemical workstation (Princeton Applied Research, AMETEK, Berwyn, PA, USA).

2.4. Corrosion Morphology Characterization

After immersion and electrochemical evaluation, the corrosion behavior of the specimens was initially confirmed through visual inspection. Field emission scanning electron microscopy (FE-SEM, Apreo 2S, Thermo Fisher Scientific, Waltham, MA, USA) was used to investigate corrosion morphology and surface changes. Quantitative analysis of the pitting morphology and volume distribution was performed using X-ray computed tomography (XCT, Zeiss Xradia series, Pleasanton, CA, USA). The acquired data underwent 3D reconstruction and quantitative analysis using VGStudio software (version 2025.3, Volume Graphics GmbH, Heidelberg, Germany). Data visualization and inspection were additionally conducted using myVGL 2025.3 Viewer (Volume Graphics GmbH, Heidelberg, Germany), which is provided for data processed by VG software (HEXAGON). By utilizing the XCT analysis results to calculate the number of pores per unit area and volume loss, the localized corrosion behavior under varying NaCl and acetic acid concentrations could be systematically evaluated.

3. Results and Discussion

The SWAAT solution primarily consists of NaCl and acetic acid, where chloride ions (Cl⁻) penetrate the aluminum surface and cause localized corrosion [37,38]. To evaluate the effect of Cl⁻ concentration on the corrosion reaction using an electrochemical method, electrochemical polarization experiments were performed in SWAAT solutions with the change of NaCl concentration from 0 to 10 wt.%. As shown in Figure 1, the corrosion potential (E_corr) progressively shifted toward more negative values with increasing Cl⁻ concentration, while the corrosion current density (i_corr) increased significantly (

Table 1. Potentiodynamic polarization curve parameters of Al1070 in SWAAT solution with different NaCl concentrations at 50 °C.

Concentration [wt.%]	Ecorr (VSCE)	icorr (µA cm−2)
0	−0.65	11.32
1	−0.75	16.00
3.5	−0.91	32.76
5	−0.99	40.21
10	−0.94	43.16

).

To investigate the effect of Cl⁻ concentration on corrosion of the aluminum surface morphology, immersion tests were conducted for 120 h in SWAAT solutions with the NaCl concentrations ranging from 0 to 10 wt.%. Figure 2a–c show partial discoloration and corrosion on surfaces immersed in low-concentration solutions, while Figure 2d,e demonstrate complete surface discoloration and intensified corrosion in high concentration solutions. This indicates that as the Cl⁻ concentration increases during immersion, the discoloration process intensifies, turning the surface white and corrosion products in the form of aluminum oxide or aluminum hydroxide adhere to the surface.

This corrosion morphology is also confirmed by the SEM presented in Figure 3, which provide a more detailed view of the degree of oxide adhesion to the surface. Under low Cl⁻ concentration conditions (Figure 3a–c), oxide formation was minimized and partial microcracks occurred, whereas under high Cl⁻ concentration conditions (Figure 3d,e), oxides formed across the entire surface and cracks were observed to have spread extensively. Notably, the adhesion of the oxide film within the crack regions suggests that chloride ions penetrated these defects, causing localized aluminum dissolution and accelerating corrosion progression [39,40,41]. When correlating these surface morphological changes with the electrochemical results presented in Figure 1, it becomes evident that increasing Cl⁻ concentration intensifies surface corrosion. Consequently, the corrosion potential shifts negatively and the corrosion current density increases significantly. Collectively, these results clearly demonstrate that Cl⁻ acts as a key factor in destroying natural oxide film of aluminum, enabling aggressive penetration into the substrate and thereby reducing local corrosion resistance [42,43].

Aluminum surfaces exposed to SWAAT conditions exhibited progressive pitting corrosion over time. Localized surface detachment was further observed, which originated from pit propagation and the accumulation of corrosion products. Under 0 wt.% NaCl (Figure 3a), the Al1070 substrate is initially protected by a bilayer passive film consisting of a compact amorphous Al₂O₃ inner layer and a hydrated AlOOH/Al(OH)₃ outer layer. This film forms spontaneously according to Reaction (1):

$$\mathrm{Al} + 3{\mathrm{H}}_2\mathrm{O} \to \mathrm{Al}(\mathrm{OH}{)}_3 + {\displaystyle \frac{3}{2}}{\mathrm{H}}_2$$

(1)

In the SWAAT environment (pH 2.8–3.0), the outer hydrated layer becomes increasingly soluble, reducing barrier protection and increasing susceptibility to chloride-induced breakdown [44]. Their adsorption locally suppresses repassivation and initiates selective breakdown, exposing the underlying metal to the electrolyte [45].

$${\displaystyle \frac{3}{2}}{\mathrm{O}}_2 + 3{\mathrm{H}}_2\mathrm{O} +6{\mathrm{e}}^{-} \to 6\mathrm{O}{\mathrm{H}}^{-}$$

(2)

Although oxygen reduction typically promotes repassivation, high Cl⁻ activity facilitates the formation of soluble aluminum–chloride complexes, as shown in Reaction (3), thereby maintaining dissolution rather than film repair [45]:

Al + 4Cl⁻ → AlCl₄⁻ + 3e⁻

(3)

Dissolved Al³⁺ ions subsequently undergo hydrolysis, producing Al(OH)₃ precipitates and further acidifying the pit interior [46]:

Al³⁺ + 3H₂O → Al(OH)₃ + 3H⁺

(4)

Rather than directly accelerating hydrogen evolution, acetic acid primarily affects corrosion by (i) suppressing repassivation through passive film dissolution, (ii) stabilizing localized acidity via acetate buffering and (iii) forming aluminum–acetate complexes that increase Al³⁺ solubility. These processes result in sustained pit activity and hinder film repair rather than functioning as a dominant driver of the hydrogen evolution reaction (HER) [46].

$$3{\mathrm{H}}^{+}+3{\mathrm{e}}^{-} \to {\displaystyle \frac{3}{2}}{\mathrm{H}}_2$$

(5)

As shown in Reaction (5) (3H⁺ + 3e⁻ → 3/2H₂), the corrosion process ultimately leads to hydrogen evolution through proton reduction, resulting in H₂ gas formation [47]. In the SWAAT environment, acetic acid functions as a proton source, increasing the concentration of available H⁺ ions and consequently accelerating the hydrogen evolution reaction. This enhancement of cathodic kinetics is presumed to intensify localized corrosion by promoting faster pit growth and repeated pit reactivation under mildly acidic conditions [48]. When these reactions are considered collectively, mechanism becomes evident: Cl⁻ ions act as the primary initiators of pitting corrosion by destabilizing the passive oxide layer and facilitating localized anodic dissolution. Simultaneously, acetic acid accelerates the cathodic reaction rate and hydrogen generation, altering the balance between anodic dissolution and film repair [49]. This combined effect explains the observed cyclic behavior of pit nucleation, propagation and corrosion product accumulation presented in Figure 4.

To evaluate the effect of acetic acid concentration on the electrochemical behavior of aluminum, potentiodynamic polarization experiments were conducted in SWAAT solutions containing 0 to 2000 μL L⁻¹ acetic acid. The solution pH showed a gradual decreasing trend with increasing acetic acid concentration (

Table 2. Potentiodynamic polarization curve parameters of Al1070 in SWAAT solution with different acetic acid concentrations at 50 °C.

Concentration [µL L−1]	pH	Ecorr [VSCE]	Epit [VSCE]	∆E [VSCE]	icorr [µA cm−2]
0	5.75	−1.10	−0.82	0.28	4.64
10	3.78	−1.06	−0.82	0.24	11.21
100	3.49	−1.05	−0.85	0.20	16.10
300	3.00	−1.05	−0.85	0.20	17.08
1000	2.47	−0.99	−0.84	0.15	21.55
2000	1.15	−0.95	−0.84	0.11	26.66

), reflecting the increase in H⁺ ion concentration due to acetic acid dissociation. This change in proton activity could indirectly affect the stability of the aluminum passive film [50]. The overall reaction between aluminum and acetic acid can be expressed as follows [51].

2Al(s) + 6CH₃COOH(aq) → 2Al(CH₃COO)₃(aq) + 3H₂(g)

(6)

The electrochemical parameter analysis results indicated that E_corr shifted slightly in the positive direction with increasing acetic acid concentration, suggesting a slight increase in the corrosion resistance. Although E_pit remained nearly unchanged across all concentrations, the increase in acetic acid led to a continuous shift of E_corr toward more positive values. As a result, ΔE (E_pit − E_corr) decreased substantially from 0.28 V at 0 μL L⁻¹ to 0.11 V at 2000 μL L⁻¹ (Figure 5b). This narrowing of the pitting potential window demonstrates an increased susceptibility to localized corrosion with rising acetic acid content. Detailed numerical values can be found in Table 2. This indicates that the probability of localized corrosion increases as the acetic acid concentration rises. Furthermore, i_corr also increased with rising acetic acid concentration, indicating accelerated corrosion rates. This acceleration is primarily interpreted as being due to the enhanced dissolution of the passive film under low pH conditions.

To evaluate the effect of acetic acid concentration on corrosion of aluminum surface, immersion tests were conducted for 96 h in SWAAT solutions with acetic acid concentrations ranging from 0 to 2000 μL L⁻¹. Figure 6 shows that after exposure, the specimen surface exhibited increased pitting formation and oxide precipitation as the acetic acid concentration increased. Particularly at high acetic acid concentrations, corrosion damage significantly intensified, showing a tendency toward accelerated corrosion rates. This intensification stems from the continuous dissolution of the natural oxide film by acetic acid. Once the Al₂O₃ film dissolves, the exposed aluminum metal is subjected to the SWAAT solution, promoting localized corrosion. Furthermore, the combined action with Cl⁻ ions present in the SWAAT environment further accelerates the breakdown of the passivation layer. Cl⁻ ions destabilize the oxide film, while acetic acid maintains an acidic environment that inhibits the film’s repassivation. The effect of these two factors is judged to be the cause of accelerating pitting corrosion [52].

The SEM image analysis was performed on specimens exposed to SWAAT solutions with increasing acetic acid concentrations from 0 to 2000 µL L⁻¹. Figure 7 shows that as the acetic acid concentration increased, the number of localized corrosion patterns and cracked areas increased. Specifically, within the 0–300 µL L⁻¹ range, a gradual increase in corrosion oxides and precipitates on the surface was observed. At 1000 µL L⁻¹, the surface appeared relatively clean, but SEM analysis revealed extensive pitting. The lack of immediately visible corrosion traces to the naked eye was judged to be due to the small pit size and low contrast, suggesting the need for more precise quantitative analysis and improved image contrast. At the highest concentration (2000 µL L⁻¹), both the number and morphology of pits increased markedly. This supports the notion that higher acetic acid concentrations promote the adsorption of corrosion products and precipitates, leading to continuous pitting and gradual growth of pitting corrosion.

To quantitatively elucidate the effect of acetic acid concentration on localized corrosion behavior, XCT analysis was conducted, as presented in Figure 8a–f. The color-coded regions indicate the volume where corrosion has progressed, allowing direct visualization of the pitting nucleation and growth process. The transition from red to blue indicates increasing pit depth. Figure 8a–c shows that at low acetic acid concentrations (0–100 µL L⁻¹), the number of pits was low. Figure 8c reveals that some pits grew larger, indicating that the initial micro-pits expanded in volume as they grew. According to the pit formation statistics per unit area presented in Figure 8g, increasing the acetic acid concentration from 0 to 300 µL L⁻¹ caused the number of pits to increase sharply from approximately <10 to about 650. This indicates that the local dissolution reaction rate is significantly accelerated within this concentration range, maximizing the frequency of pit initiation. Conversely, at 1000 µL L⁻¹, the number of pits temporarily decreased to approximately 300, then increased again to over 550 at 2000 µL L⁻¹. Furthermore, the corrosion loss analysis in Figure 8h showed that the corrosion loss started at a level of 0.00–0.02 mm³ (0–10 µL L⁻¹) as the acetic acid concentration increased, then increased to approximately 0.12 mm³ at 300 µL L⁻¹, approximately 0.17 mm³ at 1000 µL L⁻¹ and approximately 0.18 mm³ at 2000 µL L⁻¹. These quantitative changes directly demonstrate that fitting growth and dissolution rates accelerate overall as acetic acid concentration increases. This phenomenon is interpreted as a result of grown pits merging with each other, reducing the apparent number, as seen in Figure 8e–f. Furthermore, the corrosion loss per unit area shown in Figure 8h increased linearly with higher acetic acid concentrations. This suggests that as acidity increased from pH 5.75 to 1.15, the passive film dissolved, accelerating localized corrosion. These results collectively suggest that acetic acid acts as a primary factor in promoting localized corrosion by disrupting the protective oxide film and facilitating the formation, growth and coalescence of pits. To quantitatively validate this coalescence mechanism, the maximum pit volume distributions were analyzed as shown in Figure 8i. Compared to the control sample (0 µL L⁻¹), which exhibited a maximum pit volume of approximately 2100 µm³, the specimens immersed in acetic acid solutions showed a drastic increase in pit size. Specifically, the maximum pit volume surged to 25,200 µm³ (a 12-fold increase) at 10 µL L⁻¹ and escalated further to 209,100 µm³ (99.6-fold) at 300 µL L⁻¹. Most notably, despite the apparent decrease in pit count at 1000 µL L⁻¹ observed earlier, the maximum pit volume continued to expand significantly to 408,700 µm³ (194.6-fold), eventually reaching 567,000 µm³ (270-fold) at 2000 µL L⁻¹. This continuous volumetric growth, occurring inversely to the pit count reduction in high-concentration regions, strongly corroborates that individual pits are merging to form larger, more severe corrosion cavities. Taken together, the nonlinear relationship between pit number and pit volume, especially the simultaneous decrease in pit density and steep rise in maximum pit size at ≥1000 µL L⁻¹, supports a coalescence-driven pit evolution mechanism rather than simple individual pit growth or repassivation. This interpretation is further corroborated by the monotonic increase in total corrosion loss, indicating that localized dissolution continues even when new nucleation events decline. Therefore, at high acetic acid concentrations, pit propagation transitions from multiple isolated nucleation sites to fewer, deeper and merged cavities, representing a shift in localized corrosion mode driven by aggressive film breakdown and accelerated dissolution kinetics.

The corrosion mechanism of aluminum under SWAAT conditions can be summarized as follows. Referring to the Pourbaix diagram in Figure 9a, aluminum is located in the corrosion region at pH values below 4. Considering that the ASTM standard SWAAT environment in this study has a pH of 2.8–3.0, it is evident that continuous corrosion occurs. These acidic conditions compromise the stability of the aluminum oxide layer while simultaneously promoting the HER at the metal surface, accelerating aluminum dissolution. Previous electrochemical analysis showed that as acetic acid concentration increased, E_corr shifted in the positive (+) direction and i_corr tended to increase (Figure 6). This occurs because acetic acid, as a weak acid, partially ionizes in solution, increasing H⁺ concentration and thereby accelerating the cathodic hydrogen evolution reaction [53]. The activation of the cathodic reaction reduces the electrochemical polarization resistance, governing the overall corrosion rate and promoting metal dissolution. Simultaneously, the accelerated cathodic reaction also activates the anodic oxygen absorption reaction, increasing the anodic reaction. This results in effect that nonlinearly accelerates aluminum corrosion [54,55].

Cathodic reactions:

Al + H₃O⁺ ⇌ AlH⁺ + H₂O

(7)

AlH⁺ + e⁻ ⇌ AlH

(8)

Anodic reactions:

Al + H₂O ⇌ (AlOH)_ad + H⁺ + e⁻

(9)

Al → Al³⁺ + 3e⁻

(10)

AlOH²⁺ + 2H⁺ ⇌ Al³⁺ + 2H₂O

(11)

As the acetic acid concentration increases, the concentration of ionized H⁺ in the solution rises, thereby promoting the formation of AlH complexes, accelerating aluminum corrosion, and reducing overall corrosion resistance [56]. Meanwhile, chloride ions present in the SWAAT solution penetrate the oxide layer at active sites, locally destroying the passive layer and promoting pitting corrosion. When Cl⁻ ions pass through the oxide layer and reach the aluminum substrate, an anodic region forms, causing localized metal dissolution and internal stress accumulation. Repeated pitting and oxide jacking accelerate oxide layer delamination, deepening corrosion penetration and worsening surface damage. Simultaneously, acetic acid continuously dissolves the oxide film, chemically amplifying the physical damage caused by Cl⁻. It forms a thin liquid film that provides a continuous supply pathway for Cl⁻. Thus, Cl⁻ and acetic acid induce physical oxide film damage and chemical dissolution, respectively. The effect of these two factors accelerates corrosion nonlinearly (Figure 9a). Aluminum exposed to SWAAT environments risks a sharp decline in reliability due to severe breakdown of the surface protective layer and the spread of localized corrosion. The chemical basis for this corrosion mechanism is illustrated in Figure 9b, showing aluminum reacting with acetic acid to produce aluminum acetate and hydrogen.

2Al(s) + 6CH₃COOH(aq) → 2Al(CH₃COO)₃(aq) + 3H₂(g)

(12)

4. Conclusions

This study quantitatively analyzed the effects of chloride ions and acetic acid on the corrosion behavior of aluminum in a SWAAT environment. In polarization experiments, E_corr consistently shifted negatively and i_corr values increased as Cl⁻ concentration rose. Furthermore, immersion tests and SEM analysis confirmed that under high chloride ion-concentration conditions, the discoloration area and crack area increased, accelerating localized corrosion. Increasing acetic acid concentration lowered the solution pH, leading to an increase in i_corr and a decrease in ΔE, which accelerated localized corrosion. Additionally, 3D XCT analysis showed that both pit density and corrosion loss increased with rising acetic acid concentration. Cl⁻ induces electrochemical vulnerability through localized destruction of the aluminum oxide layer, while acetic acid increases aluminum surface dissolution via chemical dissolution of the oxide layer and HER promotion. The SWAAT environment is inherently very harsh for aluminum and increasing Cl⁻ and acetic acid concentrations increase the corrosion rate and localized corrosion. The NaCl concentration and acetic acid content were tested independently, the observed trends indicate a likely interaction between Cl⁻ induced pitting initiation and acetic acid driven modification of cathodic kinetics.