Pitting corrosion of aa5005 sheets produced by DC casting and twin-roll casting techniques

In this study, the pitting corrosion susceptibilities of AA5005 alloy sheets produced by the direct chill casting (DCC) technique and hot-rolling and the twin-roll casting (TRC) technique were investigated and compared. In order to compare the pitting corrosion resistances of the sheets, immersion tests, cyclic potential polarization (CPP) measurements, potentiostatic tests for the repassivation potential (Erepass), galvano–staircase cyclic polarization (GSCP) measurements, metastable pitting measurements under potentiostatic conditions and electrochemical noise measurements were performed in NaCl solutions at various concentrations. Depending on the microstructure studies, larger intermetallics were found in the DCC alloy. On the other hand, the number of intermetallics were higher in the alloy produced by the TRC technique. The immersion tests have shown that the DCC alloy have larger pits than the TRC alloy. From the CPP experiments, generally pitting potentials (Epit) of the DCC alloys were higher than TRC alloys, but the differences between the two alloy sheets were below 20 mV. Potentiostatic tests for the repassivation potential results have shown that, in general, Erepass potentials were more positive for the DCC alloys. From the GSCP measurements, breakdown (Eb) potentials and protection potentials (Eprot) of the DCC and the TRC alloy sheets were found to be close to each other. At 0.001 M concentration, the formation rate of metastable pits in the AA5005 sheet produced by the DCC technique was found to be higher than that of the TRC technique. The total charge of metastable pits in DCC alloys were generally higher. Depending on the electrochemical noise measurement, differences were found in the localized corrosion activity of the alloys of the two production techniques.