The variation of free corrosion potential of several metallic materials in natural seawaters off the coast of Qingdao and Zhoushan for 120 d was monitored by means of a home-made multi-channel potential data acquisition device. The variation of corrosion potential versus immersion time and the steady corrosion potential for every test material were peculiarly assessed. Results showed that the free corrosion potential of metallic materials in natural seawater changed quickly in the initial corrosion stage. While different kind of metallic materials presents diversified variations of corrosion potential versus immersion time. The steady corrosion potentials of tested metallic materials in natural seawater can be ranked as a series from low to high as: magnesium anode, aluminum alloys, iron castings, carbon and low alloy steels, copper alloys and stainless steels.

Keywords： metal ; natural seawater ; corrosion potential ; change rule