Influence of Titanium Additions to Aluminum on the Microhardness Value and Electrochemical Behavior of Synthesized Aluminum-Titanium Alloy in Solutions of HCl and H3PO4

Abstract

The effect of Ti content in various concentrations as an alloying element with Al on both microhardness and crystallization structure of aluminum–titanium alloys was studied, utilizing x-ray diffraction (XRD) and a scanning electron microscope (SEM). To study the electrochemical and corrosion performance of Al and its investigated alloys in 0.5 M solutions of HCl and H3PO4, two different techniques were used: extrapolation of Tafel plot and electrochemical impedance spectroscopy (EIS). Tafel plots and EIS revealed a similar trend. Generally, the rate of corrosion of the alloys was higher than that of Al. This investigation exhibited that the corrosion of Al alloying with Ti increased with an increase in both Ti content and temperature, which is due to reducing the growth of oxide film on the surface. Changes in the standard values of both entropy (ΔS) and enthalpy (ΔH), in addition to apparent activation energy (Ea) of corrosion processes of Al and its alloys in HCl and H3PO4, were evaluated. The evaluated data indicated negative values of ΔS, while the values of ΔH were positive. Besides, the decrease in ΔH value with the increase of Ti content in the alloy revealed that the dissolution of the studied alloys was fast. The positive values of ΔH were accompanied by an endothermic process. On the other hand, the activation energy (Ea) was decreased as a result of Al alloying with Ti in the two mentioned acids. Those results were supported by the corrosion current density (icorr.) and impedance parameters. By comparing the data obtained for both HCl and H3PO4 in all investigated electrodes, the corrosion current density (icorr.) in H3PO4 was lower than that in HCl. Such behavior can be ascribed to the aggressive attack of Cl¯ ions on the surfaces of the investigated electrodes, leading to pits formation.