Abstract
The magnesium lithium thermal control oxidation is a commonly used conductive anti-corrosion treatment method for aerospace. The corrosion behaviors of thermal control oxidation films for LA103Z alloys were studied in 3.5% NaCl solution. The corrosion characteristics with different immersion time were characterized by using scanning electron microscopy, energy spectroscopy, and electrochemical methods. The results showed that the corrosion of Mg-Li alloy with chemical oxidation film starts from pitting corrosion, gradually expands in depth in the early stage, forms corrosion holes, and then gradually develops into river-like morphology. In the last stage, the increasing corrosion products slow down the corrosion rate and gradually covers the entire sample surface. The corrosion product mainly consists of MgO, LiF, and MgCl2. Combined with the electrochemical characteristics, the corrosion mechanism was investigated.
Highlights
As the lightest metallic structural materials (1.30–1.65 g/cm3), Mg-Li alloys have been widely used in space fields (Wu et al, 2020a; Wu et al, 2020b)
It can be seen that when the specimens are immersed in NaCl solution, the surface forms black pits, which demonstrated that the pitting corrosion happens on the surface for 1 h
The element Mg happens in corrosion, and Li reacts further and dissolves off, which leads to the pits expanding to corrosion holes (b-c), and corrosion rate increasing as the corrosion products accumulate on the surface of the specimen (c-d), the micro-electro-battery and dissolution effect are more obvious, and the corrosion is further intensified, and corrosion develops mainly towards horizontal (d-e)
Summary
As the lightest metallic structural materials (1.30–1.65 g/cm3), Mg-Li alloys have been widely used in space fields (Wu et al, 2020a; Wu et al, 2020b). In order to satisfy the functional requirements and adapt to the space environment, it needs to take out surface treatment such as plating, oxidation, and coatings for Mg-Li alloys (Xia et al, 2019; Zhang et al, 2019; Liu et al, 2021). Many researchers have made efforts to form thin coating with good corrosion resistance (Wang et al, 2007; Chen et al, 2011; Formosa et al, 2012; Fernández et al, 2019). Fernandez et al (Fernández et al, 2019) found that reduced graphene oxide onto magnesium discs by electrochemical and chemical methods can decrease the corrosion rate. The formation of Mo on the surface of Mg alloys after chemical oxidation can significantly improve the corrosion resistance (Shao et al, 2017). Wang et al (Liu et al, 2016) used black chemical oxidation to form a film, which had uniform blackness and dense film
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