## 1 Introduction  
Due to its favorable mechanical and physical properties, low-carbon steel is widely used in a variety of applications. Its excellent weldability and machinability, and relatively low cost, make it a first-choice material in several applications, such as making pipes and structural components in the construction industry; and producing various components, such as beams, frames and supports in the automotive industry [1; 2; 3; 4; 5]. Coatings are a widely used corrosion protection method for many metals and alloys [6; 7; 4]. Coatings have several advantages and features that make them a better choice to protect metal from corrosion. Coatings can form a physical barrier that separates the metal from its environment, thus limiting the access to the metal surface of corrosive particles, such as oxygen, chlorides, and other corrosive species [8; 9]. Moreover, conversely to other methods, coatings can be applied to a wide range of metallic substrates, such as steels, aluminum, copper, and alloys, and can be customized to meet specific requirements, providing long-term corrosion protection even in highly corrosive environments [8; 9; 10; 11]. Furthermore, coatings have the advantage of being cost-effective, particularly when compared to expensive methods, such as material replacement and the repairing of corroded metallic substrates. Alkyd paints are one of the most used corrosion protection coatings, due to their excellent durability and low-cost. These oil-based paints can be applied to a variety of surfaces using several methods, such as spray, roller, or brush [12]. However, alkyld paint suffers from a low corrosion protection performance, especially when exposed to sunlight and humidity [8; 13]. One practical solution to improve the corrosion protection performance of alkyld paints is to incorporate organic or inorganic compounds into the coating formulation [14; 15]. Such a practice can significantly improve the barrier properties of the coating, making it more effective in preventing corrosive particles from reaching the metallic substrate. Additives such as nanoparticles can remarkably improve the hardness, adhesion, and durability of the alkyld paint, granting it an excellent resistance to abrasion and scratching, and reduced cracking. Many researchers have reported smart coatings that show response to a stimulant [16; 17; 18]. Smart paint can include different responses, such as self-healing, self-cleaning, corrosion-sensing, and anti-fouling, among others [19]. Among smart-coating technologies, the concept of self-healing coating was introduced as a new approach to achieving corrosion protection function. The automatic corrosion response can be designed according to various factors, such as abrasions, pH change, surface tension, and temperature. Self-repairing organic and inorganic coatings can increase the functional life of the resulting coating structure. The self-healing function can be transported, due to the presence of nano/microcontainers of polymers and inorganic particles in paint structures [20]. Magnetic nanoparticles are of great importance to researchers because of their wide range of applications, which cover many research fields, including catalysts, biotechnology, biomedicine, and data storage [14; 21; 22]. They possess excellent characteristics, such as a small size, high surface area-to volume ratio, and biocompatibility, making them the best option for many applications. The successful application of these particles depends on the stability of molecules under different conditions. For instance, the performance of magnetic nanoparticles is better when the particle size is less than the critical value. Because of the significant losses that result from the high corrosion rate of metals and alloys in corrosive acidic environments, the mechanism of corrosion protection in alloys and metals has gained a high importance, due to its durability in these environments [23].