**1. Introduction**

Metallic coatings have been applied widely to steel substrates used in the automotive industry, because of their anti-corrosion performance [1–3]. In general, coating materials are more electrochemically active than protected substrates, meaning they offer sacrificial protection. A recent technical issue in a coating system is the formation of suitable corrosion products and new phases that are effective in delaying the coating consumption and reducing the overall corrosion rate [4–6]. Regarding Al-based coatings for steel sheets, a passive film (Al2O3) forms on the coating surface, providing superior barrier protection [7–9]. In the case of AlSi-based coatings, the addition of Si decreases the thickness of the intermetallic phase at the inter-diffusion layer close to the steel substrates [10,11], which also provide good anti-corrosion performance [12]. On the other hand, Al2O3 films are unstable when exposed to environments containing chloride ions (Cl−), which can decrease the stability of the film, leading to a decrease in coating efficiency by localized corrosion [13,14]. To overcome these drawbacks, other alloying elements, such as Zn and Mg, which can modify the coating potential, are added to the Al-based coating, so that they can provide a supplementary self-healing effect by the sacrificial dissolution of alloying elements [4,5]. At the same time, several corrosion products acting as a protective barrier can be formed on the outer surface [15,16]. Hence, AlSi-based coatings with Zn and Mg are promising candidates for metallic coatings on hot-stamping steels used for auto-parts [17]. Recently, Nicard et al. [18] examined the anti-corrosion mechanism of AlSi-based coatings with Zn (2~30 wt %) and Mg (1~10 wt %). They reported that the addition of Zn and Mg to AlSi-based coatings increases the corrosion resistance in chloride-containing environments. From a practical and an industrial point of view, however, lower concentrations of Zn and Mg, which have low melting temperatures, are favored to avoid the liquid metal embrittlement (LME) phenomenon [19] and localized corrosion attack caused by the selective dissolution of these alloying elements [6,20].

Furthermore, considering the applicability of the coating to hot-stamped, high strength steel sheets used for auto-body parts, an evaluation of the corrosion resistance should proceed after the electropainting process on the metallic coating. In this regard, this study examined on the corrosion behaviors not only of AlSi-based metallic coating with 10 wt % Zn and 0.5 wt % Mg (refer to AlSiZnMg-MC, here-in-after), but also of electropainted AlSiZnMg-MC. Field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and potentiostat measurements were used to analyze the corrosion behaviors of metallic coated steels. Moreover, an accelerated corrosion test [12] was conducted on electropainted samples that had been damaged by scratching the coating with an "×" incision, and by colliding the coating surface with fine stone.
