COMPARISON OF PITTING CORROSION TENDENCY FOR CASTINGS MADE OF AL6CA, AL1FE, AL6CA1FE EXPERIMENTAL ALLOYS AND AK12M2 INDUSTRIAL ALLOY

The study covers the electrochemical and corrosion behavior of 4 alloys (wt.%): Al–6Ca (Al6Ca), Al–6Ca–1Fe (Al6Ca1Fe), Al–1Fe (Al1Fe), AK12M2. High Fe content (up to 1 %) in the alloys is required for high productivity of die-casting processes. Electrochemical tests were conducted in the 3 % NaCl aqueous solution at 26±0,5 °С using the IPC-Pro 3A (IPC-2000) digital potensiostat. Potentiodynamic anodic polarization was performed at a scan rate of 1 mV/s. The initial polarization potential was –800 mV (SHE). The potential scanning direction was reversed at a «critical» current density icr = 10 mA/cm2 with the same scan rate of polarization. The tendency of the alloy for pitting formation was determined by the Qdir/Qrev ratio (the amounts of electricity passed through the electrode before pits occur and before repassivation) and the bases of pitting resistance: difference between the pitting potential (Epit) and the equilibrium potential (Eeq); difference between the repassivation potential (Erep) and the equilibrium potential (Eeq). Corrosion tests of cast aluminum alloys were carried out by holding the samples in a salt spray chamber and in the 3 % NaCl aqueous solution for 700 h. The Olympus GX51 optical microscope was used to assess the morphology of sample surfaces after their holding. It is found that the Al6Ca1Fe and Al6Ca experimental alloys placed in the 3 % NaCl aqueous solution are not susceptible to pitting corrosion as opposed to the AK12M2 industrial alloy and Al1Fe. It is assumed that the higher corrosion resistance of Al6Ca1Fe is due to the entry of Fe into the Al10CaFe2 intermetallide. The intermetallide is not an effective cathode with respect to Fe due to significant negative potentials of Al and Ca. Al6Ca1Fe is a promising alloy for industrial use due to its high casting and mechanical properties that are not inferior to the eutectic silumin alloy and even surpass it in terms of corrosion resistance.

experimental aluminum casting alloy, intermetallides, tendency for pitting corrosion, anodic polarization

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