Abstract
The contact corrosion of couples of aluminum and mild steel was studied by electrochemical means such as corrosion current and potential measurement, rapid polarization method and electromagnetic oscillograph as well as by weight loss measurement and chemical analysis of the corrosion products.
The inorganic corrosive media used were 0.42M NaCl, 0.001M CaCl2, 0.06M MgCl2, 0.03M Na2⋅SO4, 0.0008M SrCl2, 0.42M NaCl+0.06M Mg⋅Cl2, 0.42M NaCl+0.001M CaCl2, 0.42M NaCl+0.0008M SrCl2 and the artificial sea water.
Under the experimental conditions, aluminum was generally less noble than mild steel except in alkaline MgCl2 solution.
In the artificial sea water, however, aluminum was generally less noble than mild steel and then became more noble than the mild steel in a few days, when the aluminum surface was covered with corrosion products containing iron and it was protected against further corrosion while corrosion of the mild steel proceeded spontaneously.
In most experimental conditions, aluminum sacrificially protected mild steel from corrosion, while in the alkaline MgCl2 solution aluminum was at first anodic against mild steel and the corrosion current became negligible within 2hrs due to the formation of Mg⋅(OH)2 on mild steel cathode.
