Materials Performance

DEC 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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41 MATERIALS PERFORMANCE: VOL. 57, NO. 12 DECEMBER 2018 were removed from the experiment solu- tion, rinsed with acetone, washed with deionized water, and dried in air. The frac- tured appearances and surfaces were then observed by scanning electron microscopy (SEM), model JSM-6510 † . A water bath heating method was used to control the temperature of 3.5 wt% NaCl immersion corrosion solution at 30, 50, and 70 °C (±5 °C), respectively. Electrochemical Test The electrochemical polarization curve was measured by the standard three-elec- trode method, in which the working elec- trode was an AA7003 electrochemical sam- ple, the auxiliary electrode was a platinum electrode, and the reference electrode was a saturated calomel electrode (SCE). The specimens used for the electrochemical tests were mounted with epoxy resin to provide an exposed area of 1 cm 2 and were polished with silicon carbide (SiC) papers with grits up to 1000. The specimens were t h e n r i n s e d w i t h d e i o n i z e d w a t e r, degreased in acetone and dehydrated etha- nol by ultrasound, and dried in air. After the electrodes were immersed in 3.5 wt% NaCl solutions in different temperatures for 30 min, potentiodynamic polarization tests were performed at a scan rate of 1 mV/s in 3.5 wt% NaCl solutions at different temperatures. The potential ranged from −1.4 V vs. SCE to −0.3 V vs. SCE. Electrochemical impedance spectros- copy (EIS) tests were conducted under open circuit potential. EIS was conducted in the frequency range of 100 kHz to 0.04 Hz at 10 points per decade, with a perturba- tion amplitude of 10 mV. Before the experi- ment, the surface of the sample was pol- ished to reduce the inf luence on the test results. The water bath heating method was used to control the temperature of 3.5 wt% NaCl immersion corrosion solution at 30, 50, and 70 °C (±5 °C), respectively. Results and Discussion Electrochemical Corrosion The typical potentiodynamic polariza- tion curves in 3.5 wt% solution at different t e m p e ra tu re s f o r th e D PA t e m p e r of AA7003 are shown Figure 1. The potentio- dynamic curves were fitted using Corrview † software in the mode of Tafel † , and the results are shown in Table 1. Combining the curves with the fitting results, it can be seen that the self-corrosion potential of the † Trade name. TABLE 1. POLARIZATION CURVES FITTING VALUES OF AA7003 IN NaCl SOLUTION AT DIFFERENT TEMPERATURES Aging Temperature (°C) E corr (V) I corr (A·cm 2 ) Corrosion Rate (mm/A) PA 30 –1.0648 5.1670 × 10 –5 0.56389 50 –1.0486 6.1432 × 10 –5 0.67543 70 –1.1288 9.2421 × 10 –5 1.01345 DPA 30 –1.0911 1.9434 × 10 –5 0.21336 50 –1.0134 4.4733 × 10 –5 0.48563 70 –1.0933 5.3662 × 10 –5 0.58124 RRA 30 –0.7434 1.3387 × 10 –6 0.03992 50 –1.0756 3.1125 × 10 –6 0.01457 70 –1.1822 1.2654 × 10 –5 0.13582 FIGURE 1 Typical polarization curves of AA7003 under the temper of DPA in NaCl solution at different temperatures.

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