Electrochemical Behavior of Brazed Aluminum Alloys Used in Automotive Heater Cores 2006-01-0981

The aim of the present paper was to discuss, on the basis of electrochemical results and microscope observations, the representativeness of the Nissan OY water test (acidic solution containing chloride) used to evaluate the internal corrosion resistance of heat exchangers from the cooling loop. The corrosion behavior of brazed aluminum alloys (AA4343/AA3003*/ AA4343) was investigated in neutral and acidic solutions with and without chloride by electrochemical measurements. For the three layers present in the brazed material, i.e. the residual cladding, the band of dense precipitates (BDP) and the core material unspoiled by silicon diffusion, the polarization curves were obtained in the different media. It was observed that the core material presented good corrosion resistance in neutral solutions. As a consequence and as indicated by the comparison of the corrosion potentials, the failures of the brazed material is probably linked to coupling between the different layers leading to cavernous corrosion. Conversely, in acidic solution, the polarization curves obtained for the three layers of the brazed material were characteristic of homogeneous dissolution or pitting corrosion. Consequently, although the chloride content used in the Nissan OY water appears acceptable, this study has revealed that the choice of the pH of the Nissan OY solution must be re-examined.