Effect of the Fe/Cu Relationship Corrosion and low Alloying Elements on Corrosion Behavior of Cast Aluminum Parts
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Effect of the Fe/Cu Relationship Corrosion and low Alloying Elements on Corrosion Behavior of Cast Aluminum Parts C. Rodríguez-Rivera1, J.A. García-Hinojosa1, F.J. Rodríguez-Gómez1 1
Depto. de Metalurgia, Edificio "D", Facultad de Química, UNAM, Ciudad Universitaria, D.F., C.P. 04510, México, D.F. ABSTRACT The aim of this study is to compare the corrosion rate of aluminum alloys for ornamental pieces. Three Fe/Cu relationships were tested in order to improve hardness and brightness in aluminum pieces since these alloys are used in the making of ornamental pieces. The variation on Fe/Cu content could result in modification on corrosion rate, since a metallographic characterization must be carried out identifying the presence of intermetallic phases. The presence of these elements could result in increasing corrosion rate, or even in modification of corrosion morphology, so localized corrosion could be expected. The assessment of corrosion rate was carried out in saline media, since chlorides are ions that promote localized corrosion. Electrochemical techniques (polarization curves and Tafel plots) were used in order to evaluate the attack in aluminum pieces; electrochemical impedance spectroscopy was also employed with voltage amplitude of 10 mV rms, and a frequency range from 10,000 Hz to 0.01 Hz. A typical three electrodes cell was used, exposing an area of one cm2. Before polarization, open circuit potential was monitored for an hour looking for a steady state. All conditions were tested for triplicate. The behavior of open circuit potential vs. time, and polarization curves was analyzed; a corrosion mechanism is proposed according to the electrochemical control. Polarization rate was calculated by using Tafel plots and, an electrochemical impedance spectroscopy analysis by using equivalent electric circuits is shown. Electrochemical impedance will yield information about corrosion morphology that is backed with microscopic inspection. The objective of this study is to compare the corrosion rate of aluminum alloys for ornamental pieces in order to determine the effect of the relationship Fe/Cu on the corrosion mechanism in aluminum parts for ornamental pieces. INTRODUCTION Cast aluminum alloys show very positive characteristics associated with high castability, good filling during casting in thin sections, low melting point compared with other metals, and a fast heat transfer from liquid aluminum to mold. The manufacture of ornamental pieces in aluminum casting green sand molds, generally does not require any heat treatment to obtain a specific microstructure and / or properties because of its final application, but is also relevant their finishing, color and brightness. It is therefore highly recommended their application in plates, canteens, ashtrays, lamps, and so on. With regard to corrosion of aluminum alloys with different Fe / Cu relationship, no data on the corrosion behavior has been found in literature. However, in these alloys, the copper content improves the hardness, in terms of casting and heat trea
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