GROWTH BEHAVIOR OF INTERMETALLIC LAYER ON STAINLESS STEEL IN ALUMINUM HOT-DIPPING PROCESS

A set of stainless steel plates were treated by hot-dipping into molten pure aluminum (Al) at 700 degrees C, 760 degrees C and 820 degrees C with different immersion time from 10 s to 1800 s. The growth behavior of the intermetallic compound layers between the substrate and Al coating is investigated. The intermetallic compounds showed a bi-layer structure consisting of FeAl3 close to Al coating and Fe2Al5 close to the substrate. The thickness of the intermetallic layers is closely related to the immersion time. Crack occurred with increasing immersion time and thickening Fe2Al5 layer. The thickness of the Fe2Al5 layers increases linearly with the square root of immersion time. Phase's identification of each layer was confirmed using X-ray difrraction (XRD) analysis by grinding the specimens to expose different layers. The Fe2Al5 layer exhibited a single intensive peak attributable to (002) plane. The full width half maximum (Delta omega) of Fe2Al5 on stainless steel substrate is 11.99 degrees by X-ray rocking curve measurement, suggesting that the Fe2Al5 grains have a strong orientation texture but not a single crystal. For comparison, Delta omega of Fe2Al5 formed on mild steel by hot-dipping is 14.12 degrees. The relationship between the Delta omega of Fe2Al5 layers and the growth mechanisms of crystals is discussed for the two steel substrates.