Resistance to corrosion of Al-Cu alloy in biodiesel

ABSTRACT The aim of the present work was to evaluate the susceptibility to corrosion in biodiesel of Al-Cu alloys directionally solidified: Al-4.5wt.%Cu and Al-15wt.% Cu, in function of the type of structure (columnar, equiaxed or columnar-to-equiaxed transition - CET) and chemical composition. Working electrodes were prepared with different types of alloy structures and electrochemical studies data were performed. Industrial biodiesel produced from soybean oil is used. Because of its high resistivity, for performing electrochemical tests, an aqueous extraction of biodiesel was performed, in order to obtain the aqueous ionic fraction, which generates the corrosion process. Potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) were carried out. These studies were supplemented by observations of the specimens by optical microscopy (OM). The analysis of potentiodynamic polarization curves allows to conclude that the effect of different grain structures is an evidence of the pitting potential, only in the Al-4.5wt.%Cu alloy. Impedance spectra of all samples show a double capacitive contribution. They were simulated using a R(RQ)(RQ) circuit. It was found that the resistance to charge transfer increased from the columnar zone to the equiaxed zone for the two alloys.