Microstructural evolution and oxidation resistance of hot dip aluminized layer on 20 steel were investigated during oxidization at 800 ℃ with different diffusion treatment. The results indicate that the oxidized rate at 800 ℃ is increased with extending time in the range of 2 to 6 hours when diffusion temperature is 750 ℃

while the oxidized rate is decreased with extending diffusion time in the range of 2 to 4 hours

and the minimum oxidized rate can be observed at 4 hours

then it is gradually increased with the diffusion time more than 4 hours when the diffusion temperature is 850 ℃. The desirable oxidation resistance of the hot dip aluminized layer can be obtained with the diffusion temperature of 900 ℃ for two hours. In addition

SEM observation reveals that the void in diffusion treated aluminized layer/substrate aggregates gradually into the linear crack parallel to surface

in which the internal oxidation occurs

during high temperature oxidation

which will evidently affects the oxidation resistance of hot dip aluminizing steel.