Al/Ni-plated material, which is produced by electroplating of Ni and Al on a stainless-steel substrate followed by heat-treating at 750 degrees C, has been investigated for the wet-seal material. In order to estimate the lifetime of the material, Type A and Type B were prepared, and immersion test in molten carbonate and heating test in air at various temperatures were carried out. Results of this study are summarized as follows. Two types of Al/Ni-plated material showed a good corrosion resistance against the molten carbonate at 650 degrees C in 70% air/30% CO2 for 14500 h. In the accelerated heating test, Al concentration in the Al-Ni layer kept nearly constant after 10 000 h, but voids were observed at the Al-Ni layer/the substrate interface. It was found that the growth rate of void, which was calculated from the area fraction of voids observed at each temperature, was proportional to temperature. The log k decreased linearly with 1/T, where k was a constant of the growth rate of voids. It was suggested that the lifetime of the Al/Ni-plated material is expected to be more than 40 000 h at 650 degrees C in molten carbonate.