Wear Resistance of Hot Dip Aluminum Coating on a Carbon Steel

Abstract

Influence of post annealing on the microstructure of hot dip aluminum coating on 45 steel was investigated. The wear properties of HDA steel after diffusion annealing at 1000℃ was also examined. Results show that HDA coating consisted of brittle phase Fe2Al5 as the diffusion annealing temperature was below 900℃, however which tranformed to ductile phase FeAl and Fe3 Al at 1000℃ and the coating exhibited a structural integrity and good bond with the substrate. The wear rate of the coating annealed at 1000 oC dropped significantly as the environment temperature increased from room temperature to 200℃ and 400℃, reaching an extremely low level. At room temperature, the wear rate rapidly increased with loads. At 200℃ the wear rate hardly changed with loads; the average wear rate was 4.2×10-6mg/mm.At 400℃ under the loads of 50 –200 N, the wear rate was lower than that at 200℃ under the corresponding loads. HDA steel presented excellent wear resistance at 200–400℃, owing to a 1–2 μm thick tribolayer formed on the worn surface, mainly composed of Al2O3, Fe2O3, and a bit of oxides of W and Mo. In this case the coating suffered mainly from oxidation and slight wear. However, at 400℃ as the load increased to 250 N, the tribo-layer peeled off because of which became unstable, thereby the coating spalled off, and the substate was plastically extruded.