Effect of Mg on Intergranular Corrosion of Al-Cu Alloy

Abstract

Due to high strength and light weight, 2000 series Al alloys (Al-Cu-Mg) are widely utilized in several applications such as aircrafts and automobiles. However, 2000 series alloys have limitations to use for some applications because corrosion resistance of these alloys is relatively low in commercial Al alloys. The localized corrosion is sometimes initiated at intermetallic particles. Kakinuma et.al. studied the pitting corrosion initiation at Al-Fe-Si intermetallic particles using a micro-scale electrochemical method. They clarified the effect of pH on pitting initiation 1. Also, they found that open circuit potential was changed by pit initiation and propagation 2. In addition to pitting, intergranular corrosion (IGC) should be concerned in the case of 2000 series alloys. It has been known that compositional heterogeneity related to precipitations at grain boundaries affects the occurrence of IGC.It has been known that Mg in 2000 series alloys improves IGC resistance. However, it is not clear whether Mg inhibits the initiation of IGC or the propagation of IGC. In this study, the comparison of IGC on Al-Cu and Al-Cu-Mg alloys was performed.To clarify the effect of Mg on corrosion behavior Al-Cu alloy, open circuit potential of Al-Cu and Al-Cu-Mg alloys in 0.1 M NaCl (pH 6.0) were measured for 1 h. After that, the total number of IGC and length of IGC at each site in electrode area (ca. 1 cm × 1 cm) was measured using an optical microscope. Total number of IGC on Al-Cu-Mg alloy was almost same as that on Al-Cu alloy. On the other hands, total length of IGC on Al-Cu-Mg alloy was two times shorter than that on Al-Cu alloy. It was suggested that Mg effectively suppresses propagation of IGC.Reference Kakinuma, I. Muto, Y. Oya, Y. Kyo, Y. Sugawara, N. Hara: J. Electrochem. Soc., 166(2) (2019), C19-C32Kakinuma, I. Muto, Y. Oya, T. Momii, Y. Sugawara, N. Hara: J. Electrochem. Soc., 168 021504 (2021)