目的 解决AA7075铝合金表面金属间化合物（IMCs）导致层状双金属氢氧化物（LDH）膜层生长不均匀、存在缺陷的问题,提高AA7075铝合金表面LDH膜层的腐蚀防护性能。方法 采用没食子酸（GA）对AA7075铝合金表面进行预处理,再通过水浴加热法在AA7075铝合金表面原位生长LDH膜层。通过X射线光电子能谱（XPS）分析GA预处理对AA7075铝合金表面状态的影响,并通过X射线衍射（XRD）、扫描电子显微镜（SEM）、能量色散X射线光谱（EDS）及电化学阻抗谱（EIS）,系统研究了GA预处理对LDH膜层结构、形貌、组成及防腐性能的影响。结果 经GA预处理后,AA7075铝合金表面成功形成一层GA-金属络合层,为LDH的均匀生长提供了有利条件。与未进行预处理得到的LDH膜层相比,GA预处理后表面所制备的LDH膜层结晶度显著提高,表面形貌更加均匀致密,膜层表面缺陷数明显减少,且膜层化学组成未发生明显改变,EIS测试进一步证实,膜层具备更强的防腐性能,浸泡1 h和1 d后的总电阻Rt值分别由48.86 kΩ·cm2和39.39 kΩ·cm2增加到61.25 kΩ·cm2和56.54 kΩ·cm2,浸泡7 d后仍能较好地保持LDH结构的完整性。结论 本研究证实了通过GA预处理调控表面状态以制备高性能LDH膜层的有效性,为AA7075铝合金表面高性能LDH防护膜层的制备提供了新途径。
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 (Rt) 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 Rt 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.
关键词
铝合金 /
层状双金属氢氧化物 /
腐蚀防护 /
金属间化合物 /
前处理
Key words
aluminum alloy /
layered double hydroxides /
corrosion protection /
intermetallic compounds /
pretreatment
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基金
国家自然科学基金项目（52301108）; 第十届中国科协青年人才托举工程项目
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