13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Stress Corrosion Cracking Behavior of Wrought Magnesium Alloy AZ31 and AZ61 under Controlled Cathodic Potentials Toshifumi Kakiuchi1,*, Yoshihiko Uematsu1 Masaki Nakajima2, Yuki Nakamura2, Kosuke Miyagi3 1 Department of Mechanical and Systems Engineering, Gifu University, Gifu, 501-1193, Japan 2 Department of Mechanical Engineering, Toyota National College of Technology, Toyota, 471-8525, Japan 3 Howa Machinery Ltd., Kiyosu, 462-8601, Japan * Corresponding author: kakiuchi@gifu-u.ac.jp Abstract The stress corrosion cracking (SCC) tests were performed using the wrought magnesium alloys, AZ31, AZ61 and T5 heat treated AZ61 (AZ61-T5) in a NaCl solution under the controlled cathodic potential in order to investigate the effects of the anodic dissolution and the hydrogen embrittlement on the SCC behavior. The crack growth rate (da/dt) of AZ31 was faster than those of AZ61 and AZ61-T5 under the same cathodic potential. The threshold stress intensity factor for SCC propagation (KISCC) of AZ31 was lower than those of AZ61 and AZ61-T5, and KISCC of AZ61-T5 was lower than that of AZ61, which is attributed to the difference of resistance to anodic dissolution. In AZ31 and AZ61, KISCC under the cathodic potential of -2.5 V was higher than those under the other cathodic potentials. In all materials, KISCC under the cathodic potential of -1.4 V was lower than those under the cathodic potentials of -3.0 V and -4.0 V. By the observations on the fracture surfaces after the SCC tests, less corrosion products were observed on the fracture surfaces under the cathodic potentials of -3.0 V and -4.0 V than on the fracture surfaces under the cathodic potential of -1.4 V. Keywords Stress corrosion cracking, Magnesium alloy, Hydrogen embrittlement, Anodic dissolution 1. Introduction In the recent years, light materials have been promoted to be applied in a wide variety of applications, especially in structural components of transportation machines such as airplanes and ground vehicles to reduce fuel consumption. Magnesium (Mg) alloys are the lightest among all available metals in practical use and have high specific strengths. So Mg alloys are expected as structural materials for transportation machines. However Mg alloys are sensitive to corrosion and exhibit the poor corrosion resistance compared with the other light metals such as aluminum and titanium alloys. Thus it is important to understand the corrosion properties of Mg alloys. Especially, the stress corrosion cracking (SCC) behavior is important since it could cause sudden and fatal failures. The SCC could be attributed to the combined effects of the anodic dissolution and the hydrogen embrittlement. Especially the hydrogen embrittlement plays an important role in the SCC of Mg alloys. Previously the present authors have performed the SCC tests using the wrought Mg alloy AZ31 in a NaCl solution under the controlled cathodic potential to decouple the effects of anodic dissolution and hydrogen embrittlement and have investigated the SCC behavior [1]. In the present study, the similar SCC tests were performed using the wrought Mg alloys AZ31, AZ61 and T5 heat treated AZ61 to investigate the effects of the anodic dissolution and the hydrogen embrittlement on the SCC behavior of Mg alloys. 2. Experimental details 2.1. Material and specimen The materials used were the wrought Mg alloys AZ31 and AZ61. The chemical compositions and
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