Structure and High Temperature Oxidation Resistance of Aluminizing Coating on Cast Iron

The effects of aluminum bath temperature, immersion time, and silicon content on the structure and performance of hot dip aluminum on cast iron HT200 were studied. The high temperature oxidation resistance of non aluminized, aluminized, and aluminized plus diffusion annealed samples was compared using a weight method. The structure of the aluminizing coating was analyzed using metallurgical microscopy and Xray diffraction. The results showed that the thickness of the aluminizing coating increased with increasing melt temperature and immersion time. The optimized bath temperature and immersion time were 740～810 ℃ and 5～10 min. Silicon contributed to restrain the growth of the aluminizing coating, and the coatings prepared from the baths containing 2% (mass fraction) or 6% and 9% Si had a thickness of 384 μm, 200 μm, and 121 μm, respectively. The asdeposited aluminizing coating consisted of top layer and intermediate diffusion layer (Fe_3Al majority), while the diffusionannealed coating was mainly composed of Fe_2Al_5. Moreover, the oxidation resistance of the aluminized and aluminized plus annealed cast irons was increased by a factor of 2～8 than the nonaluminized one, and the former ones had significantly increased corrosion resistance as well.