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The effects of samarium (Sm) on the microstructure and corrosion behavior of AZ91 magnesium alloy treated by ultrasonic vibration were investigated by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and electrochemical measurements. The results showed that the addition of Sm resulted in the formation of Al2Sm, which reduced the volume fraction of the β-Mg17Al12 phase and changed its morphology to fine granular. The AZ91–Sm alloys treated by ultrasonic vibration revealed relatively lower weight loss, hydrogen evolution, and corrosion current density values compared to the ultrasonic-treated AZ91 alloy prepared without Sm. Locally, a coarse β phase in the ultrasonic-treated AZ91 alloy accelerated the possibility of micro-galvanic corrosion growing into the matrix. In the prepared AZ91–Sm alloys treated by ultrasonic vibration, the fine β and Al2Sm phases reduced the probability of micro-galvanic corrosion growth and, therefore, formed a uniform corrosion layer on the surface of the alloys.

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