Influence of Al11Ce3 Size and Distribution on the Electrochemical Properties of Sonoprocessed Al-10 wt.% Ce Alloy

Abstract

Solidification of Al–Ce alloys under ultrasonic vibrations (Sonoprocessing) has a significant effect on the refining of Al11Ce3 intermetallic, which plays a key role in controlling the properties of this group of high-performance characteristics. In the current research, a group of as-received Al-10 wt% Ce alloys that were sonoprocessed under different temperatures was characterized. The influence of Al11Ce3 intermetallic size and distribution on the electrochemical properties of these alloys was investigated. Polarization tests in 3.5% NaCl solution were carried out and the recorded Tafel and impedance curves were studied. The corrosion test results were related to the microstructure characteristics as affected by sonoprocessing. Investigation of the as-received samples showed that ultrasonic vibrations broke the long lath-shaped particles of Al11Ce3 and obviously decreased their size and increased their surface area fraction. Sonoprocessing at the optimum temperature, 655 °C, reduced the Al11Ce3 particles size by 90% and enhanced their distribution in the matrix. This in its turn resulted in significant effects on their electrochemical behavior. Polarization tests showed that the corrosion rate of the un-sonoprocessed specimen decreased from ~ 0.00068 to 0.00006 mm/year after processing at the optimum condition (655 °C), and the polarization resistance increased from ~ 71 to 343 kΩ. By increasing the temperature of ultrasonic treatment beyond 655 °C, and the corresponding coarsening of the intermetallic particles, the corrosion rate slowly increased again, and concurrently, the polarization resistance decreased. The size and distribution of the intermetallic particles also influenced the formation of the corrosion pits, where the optimum sample showed shallow pits compared to those observed in the unprocessed specimen. This emphasizes the role of sonoprocessing in controlling the microstructure features and hence the electrochemical properties of Al-10 wt% Ce alloys.

Solidification Processing of Al-Ce Alloys for High-Temperature Applications

“…The first mechanism is that ultrasonic-generated bubbles grow and explode, producing strong shock waves and increasing the local pressure, thus reducing the solidification temperature, which encourages nucleation in the cavitation melt volume (Le Chatelier principle) [29]. The second mechanism assumes that when bubbles grow, and the liquid inside of them evaporates, the bubbles' temperature decreases, which causes the undercooling of the melt at the bubbles' surface, which triggers nuclei and then disperses these nuclei in the melt upon explosion (Kapustina concept) [30]. The last heterogeneous nucleation mechanism considers the cracks on substrate surfaces and the inclusions that either exist in the melt or formed upon cooling to be wetted by the melt upon bubble explosions and act as effective nucleation sites (Eskin) [23].…”

“…In the works of El-Hadad et al [17,30], solidification under ultrasonic vibration was carried out for the first time on Al-Ce alloys. An Al-10 wt% Ce alloy was processed at different pouring temperatures (645-665 • C) relative to the alloy liquidus (~644 • C).…”

“…The mechanical properties were correspondingly affected, as the specimens processed at the optimum temperature showed the best wear resistance at room and high temperatures. In [30], the corrosion behavior of the Al-10 wt% Ce alloy prepared in [30] was studied in 3.5% NaCl solution. It was found that the corrosion resistance was significantly affected by the intermetallic particle size.…”

“…Moreover, increasing the processing temperature beyond the optimum coarsened the intermetallic phase and encouraged the pitting corrosion, as observed in the microstructure in Figure 6, of the corroded samples under different processing conditions. In [30], the corrosion behavior of the Al-10 wt% Ce alloy prepared in [30] was studied in 3.5% NaCl solution. It was found that the corrosion resistance was significantly affected by the intermetallic particle size.…”

A Review on Tribocorrosion Behavior of Aluminum Alloys: From Fundamental Mechanisms to Alloy Design Strategies

“…For dilute Al-based alloys, several alloy systems have been reported with good mechanical and corrosion properties, such as Al-Mg-Bi [160], Al-Ce-X (X = Sc, Y, etc.) [161][162][163], and Al-Mg-Sc-based alloys such as Scalmalloy [164,165]. For Al-based concentrated alloys, Al0.7FeCoCrNiCux HEAs [166] and AlNiZr amorphous alloys [167] are found to be outstanding corrosion-and wear-resistant structural materials in salty environments.…”