Corrosion Behavior of Al Modified with Zn in Chloride Solution

• Published in: Materials Vol. 15; no. 12; p. 4229
• Main Authors: Calderón, Jesús Porcayo, Reyes Barragán, José Luis, Barraza Fierro, Jesús Israel, Cruz Mejía, Héctor, Arrieta González, Cinthya Dinorah, Ravelero Vázquez, Víctor, Sánchez, Kevin Piedad, Torres-Mancera, María Teresa, Retes-Mantilla, Rogel Fernando, Rodríguez-Díaz, Roberto Ademar
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 15.06.2022; MDPI
• Subjects: Adsorption; Al alloy; Al-Zn alloy; Alloys; Aluminum base alloys; Aluminum chloride; Aluminum oxide; Anodic protection; Cathodic protection; Charge transfer; Chemical reactions; Chlorides; corrosion; Corrosion potential; Corrosion rate; Efficiency; Electrochemical analysis; Electrochemical corrosion; Electrochemical impedance spectroscopy; electrochemical techniques; Electrode polarization; Electrolytes; Linear polarization; Materials selection; Mathematical models; Microstructure; Rate constants; Sacrificial anodes; Scanning electron microscopy; Solid solutions; Spectrum analysis; Surface chemistry; Uniform attack (corrosion); Zinc
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma15124229

Aluminum-based alloys have been considered candidate materials for cathodic protection anodes. However, the Al-based alloys can form a layer of alumina, which is a drawback in a sacrificial anode. The anodes must exhibit uniform corrosion to achieve better performance. Aluminum can be alloyed with Zn to improve their performance. In this sense, in the present research, the electrochemical corrosion performance of Al-xZn alloys (x = 1.5, 3.5, and 5 at.% Zn) exposed to 3.5 wt.% NaCl for 24 h was evaluated. Polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) were used to identify the electrochemical behavior. The microstructure of the samples before the corrosion assessment was characterized by means of X-ray diffraction analyses (XRD) and scanning electron microscopy (SEM). In addition, microstructures of the corroded surfaces were characterized using X-ray mappings via SEM. Polarization curves indicated that Zn additions changed the pseudo-passivation behavior from what pure Al exhibited in a uniform dissolution regime. Furthermore, the addition of Zn shifted the corrosion potential to the active side and increased the corrosion rate. This behavior was consistent with the proportional decrease in polarization resistance (Rp) and charge transfer resistance (Rct) in the EIS. The analysis of EIS was done using a mathematical model related to an adsorption electrochemical mechanism. The adsorption of chloride at the Al-Zn alloy surface formed aluminum chloride intermediates, which controlled the rate of the process. The rate constants of the reactions of a proposed chemical mechanism were evaluated.