China Aluminum Industry Network – Hot-dip aluminum coating involves immersing pre-treated metal components into a molten aluminum bath for a specific duration. After removal, a thin layer of aluminum adheres to the surface, offering protection and enhancing corrosion resistance. This process is widely used in various industrial applications, especially for steel substrates. (1) **Mechanism of Hot-Dip Aluminum Coating** The mechanism behind hot-dip aluminum is similar to that of hot-dip galvanizing. When molten aluminum comes into contact with iron-based materials, an initial reaction occurs at the interface, forming FeAl3 compounds. As the process continues, FeAl3 begins to diffuse, leading to the formation of Fe2Al5 micro-regions on its surface. With further diffusion of aluminum, the Fe2Al5 phase expands in a columnar structure, while the FeAl3 layer gradually diminishes. This intermetallic compound formation is crucial in determining the adhesion and quality of the final coating. (2) **Structure of the Aluminum-Coated Layer** The resulting coating can be generally divided into two distinct layers. The outermost layer is rich in aluminum, consisting mostly of pure aluminum or aluminum alloys. Beneath this, there is a sublayer composed primarily of Fe-Al intermetallics, with Fe2Al5 being the dominant phase. A small amount of FeAl3 may also be present. The Fe2Al5 phase tends to grow in a tongue-like manner into the base metal, which can affect the mechanical properties of the coating. Fe2Al5 is known for being hard and brittle, so it's important to limit its thickness to no more than 1/10 of the total penetration depth. Controlling the immersion temperature between 700°C and 730°C helps manage the growth of these intermetallic phases. Additionally, adding 2% to 6% beryllium (Be) to the molten aluminum can significantly reduce the thickness of the Fe2Al5 layer, improving the overall performance and durability of the coated material.
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