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 into a molten Al-12.4%Si alloy at 765oC. The effect of immersion times in the range of 60 to 900 s was investigated with respect to the phase nature, thickness, and microhardness. An uniform layer (~12 m) of Al12(Fe,Cr)3Si2 intermetallic with hexagonal crystalline structure is formed, irrespectively the immersion time. 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 of about 200 HV for the substrate, which was not affected for the investigated periods of immersion.