International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 12 Issue: 08 | Aug 2025
p-ISSN: 2395-0072
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Comparative Electrochemical Evaluation of Surface Treatments for Corrosion Protection of Marine Aluminum Kaavya Koteshwar 1Student, IB Diploma Programme, Heritage International Xperiential School, Gurugram, Haryana, India
---------------------------------------------------------------------***--------------------------------------------------------------------Abstract - This study comprehensively investigated the electrochemical corrosion protection performance of different surface treatments applied to marine-grade aluminum under simulated marine conditions. Four surface conditions were evaluated: untreated control, anodized only, painted only, and anodized followed by painting. The specimens, cut to 5 × 5 cm with a thickness of 3 mm, were exposed to half-immersion in a 3.5% NaCl solution for 21 days. Corrosion behavior was characterized using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The combined anodizing and painting treatment demonstrated the highest corrosion resistance, with an 85% reduction in corrosion current density compared to untreated aluminum. It also exhibited the lowest corrosion rate (0.012 mm/year) and the highest polarization resistance (12,450 Ω·cm²). Anodizing alone provided better protection than painting alone, but both were significantly less effective than the combined treatment. The results highlighted the synergistic interaction between anodizing and painting, where the anodized layer improved paint adhesion and offered baseline electrochemical protection, while the paint provided an effective barrier against chloride penetration. This combination offered substantial durability benefits for marine applications
2018b). Painting systems, particularly those using marinegrade epoxy primers and polyurethane topcoats, provide a physical barrier to corrosive agents and improve aesthetics (ISO, 2018a; Standard Norge, 2022). While these treatments are effective individually, the synergistic effects of combining anodizing and painting have not been extensively studied in marine-specific conditions using standardized electrochemical testing methods (ASTM International, 2023b; ISO, 2016). The aim of this work was to quantitatively compare the corrosion performance of untreated, anodized, painted, and anodized-then-painted aluminium specimens in a controlled saline environment, to understand the potential synergy between anodizing and painting, and to provide guidance on the most effective surface treatment strategies for marine applications (ASTM International, 2021; ISO, 2018a; ISO, 2018b)
2. MATERIALS AND METHODS Marine-grade aluminium sheets were sectioned into 5 × 5 cm specimens of 3 mm thickness. Four surface treatment categories were prepared: untreated control (mechanically polished to 1200 grit), anodized only, painted only, and anodized followed by painting. The anodizing process used 15% sulfuric acid at 20°C with a current density of 150 A/m² and voltage of 15–18 V for 45 minutes, followed by hot water sealing at 96°C for 30 minutes (ISO, 2018b). The painting process consisted of a zinc-rich epoxy primer layer with a dry film thickness of 75 μm and a polyurethane topcoat with a thickness of 50 μm (ISO, 2018a; Standard Norge, 2022). The coated specimens were cured for seven days at room temperature before testing.
Keywords: electrochemical corrosion, marine conditions, anodization, anticorrosion paint
1.INTRODUCTION Marine aluminium alloys have been widely adopted in shipbuilding, offshore platforms, and marine equipment due to their high strength-to-weight ratio, good machinability, and relatively low cost (Davis, 1999). Despite the presence of a natural oxide layer that provides some degree of corrosion protection, these alloys are vulnerable to the aggressive chloride ions present in seawater. In marine environments, chloride-induced breakdown of the passive film leads to localized forms of corrosion such as pitting, crevice, and galvanic corrosion (Davis, 1999; Fan et al., 2023). These processes are accelerated by fluctuating temperature, oxygen gradients, and variable pH conditions. The combined effect of these factors reduces the structural integrity and service life of aluminium components (Davis, 1999).
The specimens were half-immersed in 3.5% NaCl solution prepared with distilled water, maintained at 25°C and pH 7.0, for a duration of 21 days (ASTM International, 2021). Electrochemical testing was conducted using a threeelectrode cell, with the specimen as the working electrode, a saturated calomel electrode (SCE) as the reference, and a platinum mesh as the counter electrode. Potentiodynamic polarization scans were performed from −250 to +250 mV vs. OCP at a scan rate of 0.125 mV/s (ASTM International, 2023b; Stern & Geary, 1957). Electrochemical impedance spectroscopy measurements covered frequencies from 100 kHz to 10 mHz with a 10 mV RMS amplitude (ISO, 2016).
To mitigate corrosion, various surface treatments have been developed. Anodizing produces a thicker, denser oxide film through electrochemical oxidation, which can be further enhanced through sealing treatments (Davis, 1999; ISO,
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