The Microstructure Refinement and Strength Enhancement of Mg–Al–Si Alloy Subjected by Alternating-Frequency Ultrasonic Melt Treatment

A novel alternating-frequency ultrasonic melt treatment (AUMT) technology is used to refine the grain and improve the strength of AS41 magnesium alloy. The AUMT exhibits better grain refinement efficiency than the traditional 20 kHz single-frequency ultrasonic melt treatment method, showing the grain refinement efficiency up to 82.7%. The improvement of cavitation is suspected to be the reason for better grain refinement. The faster alternating time is beneficial to improve grain refinement efficiency. The AUMT also refines the Mg17Al12 and eliminates the agglomeration of Mg2Si. Such microstructure evolution helps improve the tensile strength and elongation of AS41.