Influence of Extrusion Temperature on the Corrosion Behavior in Sodium Chloride Solution of Solid State Recycled Aluminum Alloy 6061 Chips

Abstract

In the present work, aluminum alloy 6061 (AA6061) device chips were subjected to cold compaction monitored by an extrusion procedure at an extrusion ratio of 5:2 and elevated temperatures of 350, 425, and 500 °C, respectively. The influence of changing temperature on the corrosion of the extruded alloys after 1 h and 24 h in 3.5% NaCl solutions was studied. The polarization (cyclic potentiodynamic polarization, CPP) results indicated that the corrosion decreases with the increase of extrusion temperature of AA6061 from 350 to 500 °C. Impedance (electrochemical impedance spectroscopy, EIS) experiments provided a remarkable increase in the corrosion resistance with rising the extrusion temperature. Potentiostatic current-time (PCT) curves indicated that the current initially increased then decreased for all alloys after 1 h measurements. Prolonging the exposure time to 24 h was observed to decrease the rate of corrosion for all AA6061 alloys as proved by CPP and EIS data. This effect was found to increase the pitting corrosion as indicated by the measured PCT curves and by the scanning electron microscopy (SEM) images for the surface of the alloys. The surface layers formed on AA6061 alloys were mostly composed of aluminum oxide as presented by the spectra of the energy dispersive X-ray analyzer (EDX). All results indicated that the increase of the temperature of extrusion increased the corrosion resistance via decreasing the corrosion current and corrosion rate, and that this effect was found remarkably increased when the immersion time increased from 1 to 24 h exposure to the chloride test solution.