Potency of high-intensity ultrasonic treatment for grain refinement of magnesium alloys

An approach to assessing ultrasonic attenuation in molten magnesium alloys

“…Assuming the radiating face is fully wetted by the melt, the nominal maximum ultrasonic intensity at the radiator-melt interface is about 1700 W cm −2 at A max =30 m, where for molten magnesium = 1590 kg m −3 and c = 1500 m s −1 . 13 In general, high-intensity UT of light metals and alloys requires I Ն 80-100 W cm −2 , 2 above which fully developed cavitation occurs 2 leading to significant structural modification or refinement. Three benchmark magnesium alloys were studied: AZ91 ͑Mg-9%Al-1%Zn, hereafter all in weight percent͒ for high pressure die casting ͑HPDC͒ alloys; AZ31 ͑Mg-3%Al-1%Zn͒ for wrought alloys; and AJ62 ͑Mg-6%Al-2%Sr͒ for HPDC creep-resistant alloys.…”

“…One is cavitationenhanced nucleation and the other is cavitation-induced ͑shock waves͒ dendrite fragmentation. 2,24,25 Experimental observations obtained from ultrasonicating graphite cast iron, 2 hypereutectic Al-Si alloys, 2 aluminum alloys, 5 and magnesium alloys 13 indicate that the structural refinement is more likely due to cavitation-enhanced nucleation than dendrite fragmentation. For instance, the number density of the nondendritic primary silicon particles in hypereutectic Al-Si alloys increased dramatically after ultrasonication 2 versus without ultrasonication.…”

“…31 Recent work has shown that the model applies to ultrasonic structural refinement as well. 13,14,32 Figure 4͑a͒ plots the data of the average grain size d obtained at 15 mm below the radiating face versus 1 / Q for each alloy with respect to different amplitudes. A linear relationship was observed for each amplitude applied, in line with previous observations that Eq.…”

“…As a result, along with the rapidly growing magnesium industry in recent years, there has been an increased interest in use of UT for structural refinement of magnesium alloys. [8][9][10][11][12][13][14] However, its industrial application has been hindered by a fundamental concern, i.e., the lack of understanding and control of ultrasonic attenuation in an alloy melt.…”

Effect of Ultrasonic Melt Treatment on Microstructure and Mechanical Properties of 35CrMo Steel Casting

“…Ultrasonic energy is used to control the grain shape, grain orientation and precipitate state in the solidification process of light alloy. According to the literature [1] and literature [2], scientists found that the solidification process of AZ91 magnesium alloy could be refined obviously by introducing ultrasonic wave in the casting processing. The microstructure of 7050 and 7085 aluminum alloy could be refined and the second phase could be ameliorated by ultrasonic treatment.…”