Development of hard intermetallic coatings on austenitic stainless steel by hot dipping in an Al–Si alloy

The austenitic stainless steel was coated by dipping it into a molten Al–12.4%Si alloy at 765 °C. The effect of immersion times in the range of 60 to 900 s was investigated with respect to the crystalline structure, thickness, and microhardness of the coating. A uniform layer (~ 12 µm) of intermetallic Al12(Fe,Cr)3Si2 with hexagonal crystalline structure is formed, irrespective of the immersion time. Incorporation of Si to the coating changes the growth mode of the coating from inwards to outwards, which favours the development of a flat substrate/coating interface. Microhardness of the coating decreases with increasing dipping time, ranging between 850 and 600 HV for the shortest and longest immersion time, respectively. These hardness values are higher than that for the substrate of about 200 HV, irrespective of the immersion time.