Corrosion & Adhesion Analysis of Hot-Dip Aluminized SAE 1025 and 1045 Steel

Date : Jan 2014 - Jun 2014

In Hot-Dip-Aluminized steels, the morphology and the profile of the interface between the aluminum coating and the substrate are affected both by the composition of the molten aluminum as well as by the composition and even the microstructure, of the steel substrate. This effect has been investigated using optical and X-ray diffraction. The reaction between the steel and the molten aluminum leads to the formation of Fe-Al intermetallic compounds on the steel surface. In hot-dip-aluminizing with pure aluminum, the interlayer is ‘thick’ and exhibits a finger-like growth into the steel. With an increase in the carbon-content of the substrate steel the growth of the interlayer into the steel is impeded by the pearlite phase, whereas the ferrite phase appears to dissolve more readily. SAE 1025 and 1045 grades were coated with commercially pure aluminium by Hot-Dip Aluminizing method for the purpose of increasing its corrosion resistance in marine environments. The specimens were coated in commercially pure aluminum, at a temperature of 730º C for 20 sec, 30 sec, 40 sec, 50 sec and 60 seconds. The thickness of the coating gradually increased with the increase in the dipping time and the thickness of the inter layer compound also increased with the increase in dipping time for both SAE 1025 steel and SAE 1045 steel but the development of inter layer in 1045 steel strips was less in thickness as compared to 1025 steel strips. A maximum coating thickness of 113.812 μm was achieved for 1025 steel substrates those were dipped for 60 seconds into the molten aluminium bath and for the same dipping time, the coating thickness obtained in 1045 steel substrates was 85.24μm. The X-ray diffraction analysis was also carried out on both type of steel grades for the identification of intermetallic compound. The results of XRD shows the formation of Fe2Al5 layer beneath the Al layer.