In addition, in comparison between SEH and SE samples, although the corrosion area of SE specimens was higher than that of SEH sample, they are all rated as 5 in terms of corrosion area level. On the other hand, in terms of the number of corrosion pits, SE is less than SEH. It showed that the SEH sample might have higher potential to suffer direct corrosive attack and arise pitting corrosion than the SE sample. This is consistent with the result of EIS measurement, where SE sample shows higher corrosion resistance than SEH sample did, and it may be related to the fact that SEH has more large pores in the microstructure.