Corrosão em pistões automotivos através de técnicas eletroquímicas em solução de cloreto de sódio com diferentes concentrações

Abstract

Aluminum alloys have been widely used in the manufacture of automotive parts, due to their strength, low density and due to the formulation of different types of alloys. The objective of this research was to identify the corrosion resistance capacity of an automobile piston made. with an aluminum alloy when subjected to cyclic polarization test with different concentrations of a NaCl solution. In this work, the identification of the existing phases on the surface of the material was carried out through the EDXS energy dispersive spectroscopy technique and the microstructural characterization, through the images obtained by the MO optical microscopy and SEM scanning electron microscopy methods. In the OM analysis with 500X magnification, the presence of 4 distinct regions on the surface was observed, due to the different coloration. Subsequently, the surface was imaged with SEM to identify the chemical composition of these phases with EDXS. The measurements were made in triplicate and through its chemical composition the phases were verified based on the approximate data of the technique with the literature. Therefore, the data obtained in regions 1, 2, 3 and 4 approximated the phases Al-α, β of silica, Al9FeNi, π-Al8Si6Mg3Fe respectively. During the electrochemical measurements, the results showed that, for the most concentrated solutions of chloride (0.6 and 0.1 molL-1 of NaCl), there was a greater tendency to corrosion in open circuit potential. Due to this aggressiveness, the PCA test was carried out in a milder solution of (NaCl 0.001 molL-1 + 0.1 molL-1 of a2SO4). The sulfate solution was added to avoid the ohmic drop effects, which provided better results, being used in the cyclic polarization technique. Despite the resistance in the PCA technique, the material proved to be fragile in polarization tests due to pitting, in addition to the positive hysteresis effect observed during the trajectories of the polarization curves. In the chemical composition analysis by X-ray fluorescence, the presence of the following elements was identified: Al, Si, Mg, Cu, Fe, P Ni, which are associated with the material formulation, where their compositions must be strictly controlled to avoid the formation of corrosion piles.