Combined Effect of Ag and Mg Additions on Localized Corrosion Behavior of Al-Cu Alloys with High Cu Content

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JMEPEG https://doi.org/10.1007/s11665-020-05072-6

Combined Effect of Ag and Mg Additions on Localized Corrosion Behavior of Al-Cu Alloys with High Cu Content Jian Wang, Zhiyi Liu, Song Bai, Jing Cao, Juangang Zhao, and Diping Zeng (Submitted March 25, 2020; in revised form July 20, 2020) The localized corrosion behavior of Al-Cu and Al-Cu-Mg-Ag alloys was investigated in a naturally aerated 0.6 M NaCl solution by in situ observations and electrochemical techniques. The combined roles of Ag and Mg in affecting the corrosion resistance of Al-Cu alloys were observed using electron probe microanalysis and scanning Kelvin probe force microscopy. Results prove that Al-Cu-Mg-Ag alloy exhibits a weaker susceptibility to pitting attack than Al-Cu alloy. Such difference is ascribed to Ag and Mg atoms dissolved in Al matrix that increase the potential of the Al matrix, resulting in a smaller potential difference between the Al2Cu particles and Al matrix, that is, a weaker galvanic corrosion couple. Keywords

Al-Cu-Mg-Ag alloy, Al2Cu particle, corrosion couple, localized corrosion, difference

galvanic potential

1. Introduction 2xxx series aluminum alloys are widely used in aerospace industry due to their high strength-to-weight ratio and toughness. 2219 alloy is a traditional high-strength binary Al-Cu alloy with superior weldability, resistance to stress corrosion cracking and cryogenic properties (Ref 1, 2). These make it applicable as a structural material in the construction of liquid cryogenic rocket fuel tanks (Ref 2). 2219 alloy with 5.86.8 wt.% Cu is a high Cu-containing aluminum alloy. The microstructures of such alloy are mainly composed of the platelike h¢ precipitates and abundant Al2Cu second-phase in Al matrix, conferring high strength (Ref 2, 3). Al-Cu-Mg-Ag alloy is a novel quaternary alloy with high mechanical strength and excellent thermal stability and can be used as skins for superspeed aircrafts (Ref 4, 5). It has been well documented that Mg and Ag are indispensable for the precipitation of X strengthening phase and produce a synergistic effect on the mechanical properties of Al-Cu-Mg-Ag alloys (Ref 6-9). In general, Al-Cu-Mg-Ag alloy usually contains high Cu content

Jian Wang, Jing Cao, Juangang Zhao, and Diping Zeng, School of Material Science and Engineering, Central South University, Changsha 410083, PeopleÕs Republic of China; and Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083, PeopleÕs Republic of China; and Zhiyi Liu and Song Bai, School of Material Science and Engineering, Central South University, Changsha 410083, PeopleÕs Republic of China; Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083, PeopleÕs Republic of China; and National Key Laboratory of Science and Technology for National Defense on High-strength Structural Materials, Central South University, Changsha 410083, PeopleÕs Republic of China. Contact e-mail: liuzhi