Texture and corrosion mechanisms in aluminized steel sheet

Texture changes of aluminized coatings on steel sheet having Cr ranging from 0.0% to 1.0% in the coated layer were investigated, and corrosion mechanisms of aluminized coatings with the Cr content change in the coating layer were deduced. The aluminized coating layer without Cr consisted of two phases. The surface layer was Al and the interfacial layer between the steel substrate and the coating layer was Al5Fe2. The aluminized coating layer containing 1.0% Cr consisted of three phases. The surface layer was Al, the middle layer was Al13Cr2, and the interfacial layer was Al13Fe4 and Al5Fe2. The texture of the aluminized coating without Cr was characterized as a {001} fiber texture. As the Cr content in the aluminized layer was increased to 1.0%, the texture of the aluminized coating was not changed but the intensity of the {001} fiber texture was increased. The major orientation in the {001] fiber texture was changed from the rotated cube orientation of the 0.1% Cr contained aluminized coating to the cube orientation of the 1.0% Cr contained aluminized coating. The polarization curve indicates that the corrosion resistance was increased as the Cr content in the aluminized layer was increased For the aluminized coating without Cr, a porosity in the aluminum oxide film on the surface layer leads to preferential corrosion. After the aluminized coating layer was completely removed, the Al5Fe2 layer was selectively corroded and then the steel substrate was exposed to the electrolyte. The corrosion resistance of the aluminized coating without Cr depends on the thickness of the aluminum layer of the aluminized coating. For the aluminized coating with 1.0% Cr, the corrosion mechanism was different. After the aluminum layer was removed, the Al13Cr2 layer, which was known to be high corrosion resistant intermetallic compound, became a barrier against further corrosion. In this case, corrosion was not continued even though the same current density at which the substrate was corroded in the aluminized coating without Cr was applied. The high corrosion resistance of the aluminized coating containing 1.0% Cr was due to the existence of the Al13Cr2 layer.