where d is the aluminized layer thickness, t is the aluminizing duration, [D.sub.[infinity]] is the effective diffusion coefficient at infinite temperature, E is the activation energy, k is the Boltzmann constant, and T is the temperature.
Although SMAT can significantly reduce the aluminizing temperature, the aluminized layer formed by a single aluminizing treatment at a low temperature is still not uniform enough from place to place by a large-scale observation (Fig.
Considering the negative effect caused by the high temperature treatment and the fact that the activator is still not active enough at 400[degrees]C, a successive aluminizing process at 500[degrees]C for 120 min and then at 700[degrees]C for 60 min is employed to aluminize the SMAT Fe sample.
Figures 9a and 9b show the cross-sectional SEM morphologies of the SMAT sample after a successive aluminizing process (sample D).
Relative to the corrosion potential of the samples without the aluminizing treatment, it is decreased after the aluminizing treatment, e.g., reaching about -0.66 V for sample C and -0.68 V for sample D.
Figure 11 shows the SEM images of corroded surfaces of the original SMAT sample (sample B), and the SMAT sample treated by a single lower temperature aluminizing (sample C) and by a successive aluminizing process (sample D), respectively.
The maximum Al-diffusion depth into the SMAT sample is about 10 [micro]m after a single aluminizing treatment at 400[degrees]C.
It is anticipated that the process of the SMAT followed by a successive aluminizing treatment might be developed to significantly modify conventional aluminizing technologies to lower the treatment temperature and to greatly improve the corrosion resistance of some materials, whose corrosion resistance deteriorates after SMAT.