Effect of Gallic Acid Pretreatment on Corrosion Protection Performance of Layered Double Hydroxide Films on AA7075 Aluminum Alloy

WANG Shenao; WANG Jingjing; HUANG Congshu; LIANG Yu; CAO Yanhui; LI Hui

doi:10.16490/j.cnki.issn.1001-3660.2026.07.019

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Surface Technology ›› 2026, Vol. 55 ›› Issue (7) : 238-251. DOI: 10.16490/j.cnki.issn.1001-3660.2026.07.019

Effect of Gallic Acid Pretreatment on Corrosion Protection Performance of Layered Double Hydroxide Films on AA7075 Aluminum Alloy

WANG Shenao^1,2, WANG Jingjing², HUANG Congshu², LIANG Yu², CAO Yanhui^2,*, LI Hui¹

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Abstract

The corrosion of metals induced by chloride ions in marine environments drives the demand for effective protection of lightweight aluminum alloys such as AA7075. In-situ grown layered double hydroxide (LDH) films represent a promising corrosion protection strategy due to their anion exchange capacity, ability to host inhibitors, and strong adhesion to the metal substrate. However, intermetallic compounds (IMCs) on the aluminum alloy surface can lead to micro-galvanic effects, resulting in non-uniform LDH growth with structural defects that compromise long-term corrosion resistance. This study aims to address this challenge through a gallic acid (GA) surface pretreatment method, so as to enhance the corrosion protection performance of LDH films on AA7075.
AA7075 samples are first treated with a 0.01 mol/L GA solution for 30 s. Subsequently, ZnAl-LDH films are grown in-situ via a hydrothermal method in a solution containing 0.05 mol/L Zn(NO₃)₂ and 0.3 mol/L NH₄NO₃ at 60 ℃ for 12 hours. For comparison, LDH films are also prepared on untreated alloy substrates. X-ray photoelectron spectroscopy (XPS) confirms the successful formation of a stable GA-metal layer on the aluminum surface, which is beneficial for uniform LDH growth. The influence of this pretreatment on the resulting LDH films (GA-LDH) is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The long-term corrosion protection performance is evaluated by electrochemical impedance spectroscopy (EIS) in a 3.5wt.% NaCl solution over a 7-day immersion period, complemented by post-immersion structural and morphological analysis.
The results demonstrate that the GA pretreatment significantly improves the quality of the subsequently grown LDH film. The GA-LDH film exhibits significantly enhanced crystallinity, evidenced by stronger (003) and (006) diffraction peaks, along with a more uniform and dense surface morphology and a notable reduction in pit defects caused by IMCs. EIS measurements show that after 1 h of immersion, its total resistance (R_t) reaches 61.25 kΩ·cm², compared with 48.86 kΩ·cm² for the LDH film grown without GA pretreatment and only 7.40 kΩ·cm² for the bare alloy. After 1 d of immersion, the R_t values decrease but follow the same trend, measuring 56.54 kΩ·cm², 39.39 kΩ·cm², and 2.61 kΩ·cm² for the GA-LDH, the untreated LDH, and the bare alloy, respectively. Long-term immersion tests reveal that while the protective properties of both films decline over 7 d, the GA-LDH film consistently maintain higher impedance values. Furthermore, after 7 d of immersion, the GA-LDH film retains identifiable LDH features, whereas the untreated LDH film suffers from severe structural damage with widespread formation of corrosion products (Al(OH)₃ and Al₂O₃) and a drastic decrease in Zn content.
In conclusion, this study successfully demonstrates that a simple GA pretreatment effectively optimizes the surface state of AA7075 aluminum alloy by forming a stable GA-metal layer. This pretreatment mitigates the detrimental micro-galvanic effect of IMCs, thereby promoting the growth of a denser, more crystalline, and less defective ZnAl-LDH film. The resulting LDH film exhibits significantly improved corrosion protection performance and long-term stability in chloride-containing environments. This facile and effective pretreatment strategy provides a valuable new pathway for developing high-performance LDH-based protective coatings on high-strength aluminum alloys.

Key words

aluminum alloy / layered double hydroxides / corrosion protection / intermetallic compounds / pretreatment

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WANG Shenao, WANG Jingjing, HUANG Congshu, LIANG Yu, CAO Yanhui, LI Hui. Effect of Gallic Acid Pretreatment on Corrosion Protection Performance of Layered Double Hydroxide Films on AA7075 Aluminum Alloy[J]. Surface Technology. 2026, 55(7): 238-251

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