Effects of a new pre-milling coating process on the formation and properties of an Fe–Al intermetallic coating

In this study, a new coating process was developed using mechanical milling. The new coating technique was named the pre-milling coating process and was used for the formation of Fe–Al intermetallic coating on low-carbon steel substrates. In this new coating process, AA7075 aluminum-alloy powders were milled for various periods (4 h, 8 h, 12 h, 16 h, 20 h, and 24 h) in a vial and then milled onto low-carbon steel for another 4 h to form a coating on the steel substrate. Local intermetallic formation was analyzed with scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The XRD and SEM observations indicated the presence of compounds such as FeAl, Fe2Al5 and FeAl3 at distances of 6 μm, 16 μm and 25 μm from the substrate surface, respectively. The results revealed that the best coating thickness distribution, pore content and microhardness values were produced by the formation of Fe–Al intermetallics after 16 h of pre-milling and 4 h of coating (for a total of 20 h milling time).