Sulfosalicylic/oxalic acid anodizing process of 5854 aluminum-magnesium alloy: Influence of sealing time and corrosion tendency

Abstract

In this paper, anodizing process of 5854 aluminum-magnesium alloy (5854Al-Mg) in oxalic acid (OXA) was investigated in the absence and presence of 5-sulfosalicylic acid (SSA). Electrochemical and surface morphological techniques were used to study the corrosion resistance and film characterizations. Furthermore, the influence of sealing time on corrosion rate was addressed. It was observed that the corrosion current density decreased with the addition of SSA and increasing with sealing time. Maximum coating efficiency was 90.72% in the presence of 0.09 M SSA at 50 min of sealing period. The open circuit potential (OCP) was shifted to a more positive direction indicating the formation of passive film. While, the values of polarization resistance (Rp) of aluminum alloy were higher in the presence of SSA. Scanning electron microscopy (SEM) showed that the addition of SSA improved the surface properties. The anodizing of 5854 Al alloy in the presence of SSA resulted in the formation of anodic films of higher hardness, less roughness, and high film thickness as compared with OXA alone. Reaction kinetics models were proposed. The best fitting was obtained with zero-order reaction kinetics. Half-life time was increased from 9.05 to 123.3 min in case of OXA/SSA anodizing process. In addition, four mathematical equations were suggested to represent the corrosion current density as a function of time. Power model was the most significant one as compared with linear, second order, and exponential models.