Sacrificial Anode Cathodic Protection of Aluminum-Coated Steel for Automotive Mufflers

To apply a sacrificial anode cathodic protection system to automotive muffler materials, the reliability of various sacrificial anode materials and their protective ability were evaluated by conducting laboratory tests in synthetic condensed water. Three kinds of sacrificial anodes were selected for the anode performance evaluations: Al, Zn, and Mg. The muffler materials were Al-coated steel and uncoated steel. The corrosion behavior of the muffler materials and sacrificial anodes in synthetic condensed water was investigated by conducting potentiodynamic tests. The cathodic protection ability was evaluated using the weight-loss test. The results of the potentiodynamic test indicated that Al was less suitable for the sacrificial anode because it became passive. Mg was also disqualified due to its high dissolution rate. However, Zn was found to be suitable for the sacrificial anode because of its low dissolution rate, high stability, and satisfactory potential difference. The results of the weight-loss test demonstrated that the corrosion rate of Al-coated steel was reduced from 0.03 mm/y to 0.002 mm/y, and that of uncoated steel from 2.39 mm/y to 0.02 mm/y by the coupling with the Zn anode. In addition, the proper area ratio of the cathode-to-anode was 10:1. From these results, it can be concluded that the Zn anode can protect both the Al coating with passivation and the steel substrate with a low dissolution rate.