The Influence of Mg and Cr Addition on the Anodizing and Electrochemical Behaviors of 5xxx Al Alloy

摘要

The influence of Mg and Cr content on color of anodized films on 5xxx Al alloys was analyzed. Furthermore, measurements of potentiodynamic polarization curves (PDS), electrochemical impendence spectroscopy (EIS) and scanning electron microscopy (SEM) were utilized to investigate the effects of Mg and Cr addition on the corrosion and electrochemical behavior of 5xxx Al alloy in H_2SO_4 or NaCl aqueous solution. The results of the anodizing treatment showed that with Cr addition, the color space b*-value of anodized film increases and the color of the film becomes yellower. However, the b*-value of anodized film decreased with increasing Mg content. The results of electrochemical tests showed that 5xxx Al alloy was more susceptible to corrosion with Mg addition due to a decrease of corrosion potential and impedance, and more resistant to corrosion with Cr addition. During the corrosion process, the initial corrosion attack took place on interfaces with a potential drop, such as interfaces between matrix and Mg-Si or Al-Fe particles. In the chloride solution, the increase of chloride concentration promotes the formation and propagation of pitting, and thus the corrosion resistance of 5xxx Al alloy dropped.