The hot corrosion resistance of hot-dip aluminized low carbon steel with nickel interlayer under static load

The failure mechanism of hot-dip aluminized (HDA) low carbon steel with nickel interlayer under static loading was studied. The nickel interlayer was plated using electric method with a current density of 1.8 A/cm(2) for 10 min in Watts bath, followed by hot-dipped in molten pure aluminum (> 99.5%) for 10 s at 700 degrees C. The specimens were smoothly deposited with 2 mg/cm(2) of NaCl/Na2SO4 salt mixture, with a portion of 50/50 wt% ratio. The tensile test in hot corrosion, induced by salt mixture, was carried out by applying a static load at 750 degrees C. The results show that the intermetallic layer of Ni/Al exhibits high adhesion and formability while the elongation of gauge length rising to 7%. Owing to the inter-diffusion between Ni/Al, the intermetallic layer gradually changes to laminar structure with higher nickel content which also contributes to enhance the performance. However, hot corrosion induced by salt mixture reduces the amount of aluminum on the outer layer lowering the thickness of Ni/Al intermetallic layer. As the perpendicular cracks formed, the salt mixture penetrates to the interface between substrate and coating layer causing the oxidation of the carbide and accelerating the phenomenon of break away. Overall, the HDA with nickel interlayer on low carbon steel improved the lifetime to about 5 times compared to bare material.