The Corrosion Behavior of Carburized Aluminum Using DC Plasma

Because of the outstanding properties of aluminum, it is widely used in today's advanced technological world. However, its insufficient wear resistance limits its use for commercial and industrial applications. In this study, we performed DC diode plasma carburizing of aluminum in the gas composition of CH4–H2 (20–80%) and at a temperature of about 350°C for 4 and 8 hours. The corrosion properties of the untreated and plasma-carburized samples were evaluated using anodic polarization tests in 3？N HCl solution according to ASTM: G5-94. The metallurgical characteristics were then investigated using XRD and SEM. The results showed that the carburizing process improves the corrosion resistance of treated specimens at low temperature. 1. Introduction Though aluminum is a thermodynamically reactive metal, it has an excellent corrosion resistance. This is due to the formation of a compact and adherent oxide film on the surface. Because of this, it is used in many applications such as buildings, power lines, transportation field, and food and chemical industry. The oxide film is passive in the pH rage of about 4 to 8.5, but it easily dissolves in highly acidic or alkaline corrodents [1]. Moreover, it is not homogeneous and contains weak points at which localized corrosion may occur in environments containing halide ions such as seawater and offshore [2, 3]. Hence, there are some restrictions in application of aluminum and its alloys in modern industries. The danger of localized carrion attack can be decreased by surface modification, which will decrease the number of possible localized attacks to minimum. It has been shown that the surface properties of Al can be improved by the formation of a carbide surface layer [4, 5]. The Al4C3 compound provides strength to the composite materials and alloys like Al-Al4C3, Al-SiC-Al4C3, and Al-Al3Ti-Al4C3 [6]. For this purpose, various processing technologies have been developed such as carburizing by plasma which takes place in a glow discharge region. In this process, the aluminum samples are bombarded by positive carbon ions. These ions penetrate into the surface of aluminum and form the Al4C3 compound which is resistant to chemical corrosion. Aluminum has low melting point of about 660°C, and the carburized layer is formed in temperatures not more than 350°C. Different methods have been used for the formation of a carbide layer such as ion implantation, carburizing in a plasma environment and in a plasma spot which is used for aluminum carburizing, using energetic carbon ions emitted from a low-energy (1.5？kJ) Mather