Temperature effects in aluminium melts due to cavitation induced by high power ultrasound

Abstract

Extensive research has been carried out previously in ultrasonic (cavitation) melt treatment. Such treatment can reduce grain size and improve material homogeneity. However, it is still not well understood which of the mechanisms is responsible for cavitation aided grain refinement. For better understanding of the processes which take place during solidification under the influence of ultrasonic vibrations, it is very important to consider the change in the cooling conditions during such treatment and thermal effects which are generated in the cavitation zone and in the bulk of liquid. The current paper presents the results of an experimental work on temperature effects in aluminium alloys and their impact on resultant microstructures. The results are discussed based on heat flow, nucleation and fragmentation during solidification.

Criteria of Grain Refinement Induced by Ultrasonic Melt Treatment of Aluminum Alloys Containing Zr and Ti

“…In (Figures 1 and 2). [20] Similar effects were observed by other researchers in a wide range of materials: foundry and wrought alloys based on aluminum and magnesium, pure zinc, ferritic, austenitic, carbon, and high-boron steels, nickel-based superalloys, and stainless steels, etc. [2,7] This effect is explained by active melt movement along with the introduction of ultrasonic energy by cavitation, [2] which creates the conditions when dendrites continuously simultaneously grow and fragment so that the solid phase is formed more uniformly through the solidification range.…”

“…[2,7] This effect is explained by active melt movement along with the introduction of ultrasonic energy by cavitation, [2] which creates the conditions when dendrites continuously simultaneously grow and fragment so that the solid phase is formed more uniformly through the solidification range. [20] Experiments in situ with sonocrystallization of ice in sucrose solutions demonstrated dendrite fragmentation caused by ultrasonic streaming. [21] Another possible reason for structure refinement is the formation of a solidified shell on the surface of a vibrating ultrasonic horn.…”

“…[2] However, the investigations on the influence of cavitation treatment in aluminum alloys with high amount of Zr demonstrate that Zr alone does not increase the efficiency of UST. [22] Only when Zr was added together with small amounts of Ti was the grain size decreased significantly. [22] Further investigations showed that already small additions of Ti, i.e., 0.015 mass pct Ti, can dramatically change the grain structure of Al-Zr alloys solidified in the presence of ultrasonic field ( Figure 5).…”

“…[22] Only when Zr was added together with small amounts of Ti was the grain size decreased significantly. [22] Further investigations showed that already small additions of Ti, i.e., 0.015 mass pct Ti, can dramatically change the grain structure of Al-Zr alloys solidified in the presence of ultrasonic field ( Figure 5). The grain size decreases as the concentration of Ti rises.…”

Ultrasonic Treatment of the 304 Stainless Steel Melt

“…Nowadays, the application of ultrasonic treatment on metal solidification is becoming more and more common, and substantive research results have been achieved about refining the solidification microstructure. Osawa et al 12) applied ultrasonic treatment in the solidification of AZ91 alloy, as a result, fine and uniform microstructure was obtained, meanwhile, the yield strength and tensile strength were both improved significantly as well; Atamanenko et al 13) carried out experiments to investigate the process of aluminum melt treatment using ultrasound, and determined the effect of cooling temperature on the refinement of microstructure during solidification. However, the melt with high temperature would corrode the booster which plays a very important role in introducing ultrasound into molten metal, for this sake, the research of refining microstructure with ultrasound mainly focused on low-melting-point metal, [14][15][16][17][18][19][20] there is relatively less research about the effect of ultrasonic treatment on the highmelting-point metals, such as steels.…”