13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- correspond to the corrosion region, except for the AZ61 specimen under the cathodic potential of -1.4 V. Fig. 7 shows the relationship between the crack growth rate, da/dt, and the stress intensity factor, KI. Crack growth rates of AZ31 are much faster than those of AZ61 and AZ61-T5, and those of AZ61-T5 are faster than those of AZ61 under the same cathodic potentials. The crack growth rate of AZ31 is not sensitive to the change of KI values especially under the cathodic potential of -3.0 V. The relationship between the threshold stress intensity factor for the SCC propagation, KISCC, and the cathodic potential, E, is summarized and shown in Fig. 8. In AZ31, KISCC under the cathodic potential of -2.5 V is higher than those under the cathodic potentials of -1.4 V and -3.0 V. This tendency is the same in AZ61, i.e., KISCC of AZ61 under the cathodic potential of -2.5 V is higher than those under the other cathodic potentials. In AZ61, KISCC under the cathodic potential of 0 V is the same as that under the cathodic potential of -1.4 V. In all materials, KISCC under the cathodic potential of -1.4 V is lower than that under the cathodic potentials of -3.0 V and -4.0 V. 0 50000 100000 0 0.01 0.02 –1.4V –3.0V Time t (s) Crack length a (m) Magnesium Alloy –2.5V 3% NaCl solution Semi–solid: AZ61–T5 Double: AZ61 Open: AZ31 0V –4.0V Figure 6. Relationship between crack length, a, and testing time, t 7 10 20 10–8 10–7 10–6 10–5 10–4 Stress intensity factor KI (MPam 1/2) Crack growth rate da/dt (m/s) 40 –1.4V –3.0V –2.5V Open: AZ31 Double: AZ61 –4.0V Magnesium alloy 0V Semi–solid: AZ61–T5 3% NaCl solution Figure 7. Relationship between crack growth rate, da/dt and stress intensity factor, KI
RkJQdWJsaXNoZXIy MjM0NDE=