Corrosion Characterization of Silicon Carbide and Fly Ash Particulates Dispersion Strengthened Aluminium 5083 Composites

Abstract

Corrosion behavior of aluminium metal matrix composites is a major study aimed at evaluating the potential of using the materials for aerospace components. Aluminium 5083 is a specific class of alloy which is known for its corrosion resistance in extreme environments and is used in aerospace components. However, the studies on effect of reinforcements such as silicon carbide and fly ash on corrosion behavior of aluminium 5083 alloy has not yet been carried out; even though there are sufficient literature available to give an overview of the mechanical and tribological characteristics, the corrosion characteristics of the composites are not yet studied. The present work involves the fabrication of aluminium-silicon carbide-fly ash composites and study of the corrosion behavior of these composites. The composites are prepared by stir casting technique, with the composition of the silicon carbide particulates varying in the range of 3 to 9 wt% at an interval of 2% each for every addition. The percentage of fly ash is taken constant at 5% for limiting the scope of our study after successive trials and errors. The composite specimens thus prepared are evaluated for corrosion by different test methods namely, weight loss test, open circuit potential test, potentiodynamic test. The weight loss technique involved the process of preparation of cylindrical specimens of standard size (20 mm diameter and 20 mm length), and suspending them in hydrochloric acid (HCl) and sodium hydroxide (NaOH) medium for a duration of 120 h (5 days), taking note of the weight loss for every 24 h, and corrosion rates are henceforth computed using an empirical relation discussed further in the paper. There is a reduction in the corrosion rate with the increase in percentage of silicon carbide from 24 to 120 h and it almost reached a constant state at the end of 120 h. The open circuit potential test is carried out using a circuit consisting of a multimeter, the specimen of 1.5 cm length, 1.5 cm width and 2 mm thickness (one of the electrode) held by an aluminium wire with teflon tape wound around it, calomel electrode. The DC voltage developed after dipping them in NaOH and HCl solutions (electrolytic medium) is measured using the multimeter and it shows a decrease in the potential with the increase in the percentage of silicon carbide from 3 to 9%. Furthermore, the potentiodynamic test is conducted using a test setup consisting of five mouth flask with calomel electrode and a working electrode (i.e., the specimen connected to a copper holder and covered with Teflon tape barring an area of one square centimeter exposed to the electrolyte). The anodic and cathodic potentiodynamic polarization measurements are obtained in the form of tafel plots in the computer that is interfaced with the test setup. The results reveal that the corrosion current (Icorr) increases with the increase in the percentage of silicon carbide in the matrix. The electrolyte chosen for potentiodynamic test is NaOH and HCl. The concentrations of both the acid and alkaline solution in present work are taken at 1.0 M.

Keywords: Corrosion, aluminium, metal, matrix, composite, potentiodynamic, open circuit, potential