Interfacial Microstructure and Corrosion Behaviour of Mild Steel Coated with Alumina Nanoparticles Doped Tin Composite via Direct Tinning Route

The improvement of the surface properties of ferrous metallic materials has become a crucial criterion for advanced engineering applications. The interfacial microstructure and corrosion behaviour of mild steel coated with alumina nanoparticles doped in tin composite using the direct tinning technique were investigated. A coating layer of tin composite containing different loads of Al2O3 nanoparticles (0.25 wt.%, 0.50 wt.%, 1.00 wt.% and 1.5 wt.%) was prepared and directly deposited on a mild steel substrate. This type of a direct tinning process is considered to be a simple and low-cost route for protecting metallic materials from corrosion. It was found that the thickness of both the composite layer and Fe-Sn intermetallic layer at the coated interfaces was highly affected by the presence of alumina nanoparticles that effectively inhibit the diffusion of Sn atoms into the Fe substrate. For the samples coated with lower content of alumina nanoparticles (0.25 wt.% and 0.50 wt.%), the thickness of the Fe-Sn intermetallic coating (IMC) layer is decreased due to Fe-Sn IMC suppression. Otherwise, for the addition of more alumina nanoparticles (1.00 wt.% and 1.50 wt.%), the thickness of the Fe-Sn IMC layer is slightly increased because of nanoparticle’s agglomeration and flotation. It can be reported that the presence of alumina nanoparticles in the coating layer improves, to a great extent, the corrosion resistance of Sn-composites surface on mild steel substrates. Although the tin composite coating layer with a high quantity of alumina nanoparticles (1.0 wt.%) exhibited better corrosion resistance than the other tested samples, such nanoparticle additions have become increasingly difficult to obtain. It was observed that the Al2O3 nanoparticles agglomeration and flotation that were detected in the coating surface may be related to high fraction nanoparticles loading and to the difference in the gravity for Sn and Al2O3 nanoparticles. However, based on our investigation, a coating layer that contains 0.50 wt.% alumina nanoparticles is highly recommended for achieving long lasting and high-performance corrosion resistance for coated mild steel with minimal coating layer defects.