Hot dip aluminising of low carbon steel was done at temperatures 690°C and 750°C for dipping time ranging from 300 to 2400 seconds. During aluminising a mixture of ZnCl2 and NH4Cl was used as flux. During aluminising components of the flux decomposed and zinc formed interacted with the Fe and Al. The aluminised samples were characterised for iron-aluminium intermetallic layer formation, morphology, and local composition. It was observed that intermetallic layer was predominantly Fe2Al5 and FeAl3 at 690°C and at 750°C coating consisted of FeAl3 layer and a layer with Al/Fe ratio greater than 3.26. For both temperatures, coating thickness increased with increase in time. For a given dipping time, deposition was less at higher temperature and this is attributed to changes in the kinetics of growth of individual layers due to dissolved zinc in the aluminium, at 750°C. Also, spalling of intermetallic layers was observed at elevated temperatures and longer dipping times. 1. Introduction Steel remains the material of choice for numerous applications, largely because of its low cost and wide variety of properties available through alloy design, heat treatment, and amenability for forming operations [1]. The oxide layer forming on the steel substrate is a noncompact one and due to this conventional mild steel exhibits poor oxidation and corrosion resistance properties. To improve corrosion properties, the steel can be alloyed with various elements such as chromium and nickel, but this increases material cost and limits width of the processing window [1]. Alternate route is to modify the surface of the steel appropriately, so that it can replace expensive alloy steel material [2]. During surface modification, the surface of the steel material is modified over a relatively shallow depth, using an appropriate method. When a suitable technique is selected and correctly done, the following properties of the steel can be increased: resistance to wear, chemical resistance, mechanical resistance, and oxidation resistance [3, 4]. Among various surface modification methods available for steel, the hot dipping process has drawn much attention because it is an effective and inexpensive process. In this context, use of aluminium as a coating material is highly relevant because, aluminium, when applied to steel provides corrosion resistance layer [5]. Also, aluminium bearing steels can be easily nitrided and nitrided steel has better wear and fatigue properties. Continuous alumina layer is highly resistant to oxidation, sulfidation, and degradation in chloride containing
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