Abstract: Microstructure of hot dipping aluminized layer on X80 steel was improved by adding Cu element to the hot dipping aluminizing bath. Diffusion annealing experiments were carried out at different temperatures to investigate the affecting mechanisms of annealing temperature and copper element on microstructure of the aluminized layer by means of scanning electron microscope and X-ray diffractometer. Smile View software was used to measure the thickness of aluminized layer. The results show that during hot dipping aluminizing, the addition of Cu reduces the tongue-and-groove morphology between the alloy layer/X80 steel substrate interface to make the interfacial reaction more uniform. The thickness of the brittle Fe₂Al₅ alloy layer is minimum when the Cu content is 1% (mass fraction). With the increase of diffusion annealing temperature, the interface uniformity of the specimen with 1%Cu addition increases. When the diffusion annealing temperature is ≥600 ℃, a very thin FeAl phase layer begins to appear in the diffusion layer. When the diffusion annealing temperature is ≥650 ℃, the free layer disappears, the uniform FeAl layer appears in the diffusion layer and the holes appear outside the diffusion layer. When the diffusion annealing temperature is 700 ℃, the middle of the FeAl layer has a hole zone, and the outside of the diffusion layer has large holes. The addition of 1%Cu to the hot dipping aluminizing bath reduces the difference of migration velocities between Al and Fe atoms during diffusion annealing, thereby reducing the concentration gradient between Al and Fe atoms, which results in a more homogeneous interfacial reaction, thus avoiding the appearance of holes in the infiltrated layer.

Key words: hot dipping aluminizing, X80 steel, Cu, microstructure, interfacial reaction