Effects of Ultrasonic Treatment on Grain Refinement and Gas Removal in Magnesium Alloys

Abstract

The effects of ultrasonic treatment on grain refinement and hydrogen removal in three kinds of magnesium alloys—Mg-3Ca, Mg-6Zn-1Ca, and AZ80 alloys—were investigated in this study. After ultrasonic treatment, the grains of the magnesium alloys were refined to varying degrees. The degassing effect was characterized by measuring the densities and hydrogen content of ingots. The results indicated that the application of ultrasonic treatment in these magnesium alloys was able to remove hydrogen and obviously refine the microstructure. In this experiment, both the measurement of the density of the ingots and the solid-state hydrogen measurement reflected the degree of degassing. The highest degassing efficiencies were 53.8%, 67.5%, and 34.9% for the Mg-3Ca, Mg-6Zn-1Ca, and AZ80 alloys, respectively. The lowest hydrogen content of the AZ80 alloy reached 8.2 cm3/100 g, and the corresponding tensile strengths were 174 Mpa, 79 Mpa, and 6.2%, which represented increases of 41.5%, 38.6%, and 87.9%, respectively. The cavitation effect and acoustic streaming effect with an appropriate ultrasonic treatment duration resulted in grain refinement, degassing, and the uniform dispersion of second phases. This can significantly improve mechanical properties and provide a basis for industrial production.

Investigation on the Duration of Action of Mg3N2 as a Grain Refiner for AZ80 Alloy

“…However, the grain refinement approach with zirconium [4], which is commonly used for non-Al-containing Mg alloys, does not work for this AZ Metals 2024, 14, 485 2 of 11 alloy family due to the formation of an AlZr intermetallic phase, which is ineffective for the grain refinement of Mg alloys [1]. Other grain refinement methodologies (i.e., rapid cooling, melt superheating, carbon inoculation [5][6][7], the addition of Al-Ti-C [8], B [9], Al-V-B master alloy [10], CaO [11], MgO [12,13], SiC [14], VN [15], Mg 3 N 2 [16][17][18], AlN [19], TiB 2 [20], Ca [21], the application of ultrasonic treatment [22]) have therefore been widely investigated, with a focus on the effect of particles on the grain restriction factor [23][24][25][26] and dendritic grain growth [27] as well as phase growth [28,29]. However, rapid cooling may not be a viable option for particular castings, while superheating uses extra energy and increases the oxidation of the melt.…”