Ultrasonic Degassing of Aluminium Alloy Melts

Aluminium and alloy melts can be efficiently degassed using high-performance ultrasonication. Powerful ultrasound waves promote the coalescence of hydrogen and other unwanted gases so that they can be removed efficiently from the metal melt. Ultrasonic degassers are available for the application at very high temperatures and heavy duty.

Ultrasonic Degasification of Molten Aluminium Alloys

The generation of cavitation in liquid metals is a highly demanding application and there are only very few techniques to produce sufficient and reliable cavitation in metal melts. However, the rate and intensity of cavitation are a crucial factors shaping the degasification results. Effective degasification requires reliable cavitation in order to obtain maximum structural refinement of the metal melt. Intense acoustic cavitation generated by high-performance ultrasound can improve the degassing by 30 to 60%. At the same time, sonication can improve the grain refinement of metal melts significantly.

Advantages of Aluminium Alloy Melt Degassing using Ultrasonics

Since degassing of metal melts such as aluminium alloys is a demanding task, that heavily influences the quality of metals and die casts, degassing using power ultrasound is considered a promising method – especially in regards to its advantages.

  • Effective removal of gas bubbles: Ultrasonic-probe degassing is a very effective method of removing gas bubbles from metal melts. The high-frequency ultrasonic waves cause the bubbles to rise to the surface of the melt and escape, leading to a significant reduction in the gas content of the melt.
  • Improved material properties: The removal of gas bubbles from metal melts can lead to significant improvements in the mechanical and physical properties of the resulting material. This is because gas bubbles can act as stress concentrators, leading to reduced strength and ductility.
  • Improved casting quality: Ultrasonic degassing can also improve casting quality by reducing porosity and other casting defects associated with gas bubbles.
  • Less dross: Ultrasonic degassing results in less dross. Therefore, the ultrasonic degassers make the application of metal degasification more efficient.
  • Grain refinement: Ultrasonication is additionally used to improve the grain structure of metal melts. Thereby, metal quality is further enhanced.


Process Parameters of Ultrasonic Degasification: Ultrasonic probe-type degassers are considered to be one of the most reliable outgassing methods, which have been proven scientifically viable on small and large scale. The generation of intense acoustic cavitation depends on various factors including ultrasonic process parameters, metal composition, surface tension, melt temperature, viscosity, as well as volume and dissolution level of gas inclusions in the metal melt. Ultrasonic process parameters can be precisely tuned to the metal melt composition and the influencing factors so that the right intensity of cavitation is obtained. The exact adjustment of the ultrasonic parameters are the fundamental for the advantages of ultrasonic degasification of metal melts. The main advantages of ultrasonic degassing include high degassing rates and the reduced environmental impact of the process. Since ultrasonic degasification results only in very little dross, ultrasonic metal melt degassing is a green, environmental-friendly technique.

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Ceramic sonotrode BS4D22L3C is a special sonotrode suitable to sonicate high-temperature liquids such as molten aluminium (e.g. for mixing and degassing). Made by Hielscher Ultrasonics

Ceramic sonotrode BS4D22L3C is a special sonotrode suitable to sonicate high-temperature liquids such as molten aluminium (e.g. for mixing and degassing).

Degassing Aluminium and Alloy Melts with Ultrasound

Ultrasonic degassing is a proven method to increase aluminium alloys density and decrease hydrogen contents in aluminium alloys. In comparison to alternative degassing procedures such as outgassing by using a rotary impeller, ultrasonic degassing excels by speed and efficiency. Studies have shown that an ultrasonic probe degassing system was about 3 times faster than impeller-driven gas removal.
As ultrasonic degasification does not involve conventional metal stirring, the protective aluminium oxide on the surface of the melt is not disrupted. Keeping the aluminium oxide layer intact prevents the introduction of aluminium oxide into the aluminium melt so that it maintains it protective effect against atmospheric contaminants. Ultrasonic degassing improves the grain refinement and structure of aluminium alloys. This in addition to the ultrasonically promoted removal of non-metallic gas inclusions from the liquid aluminium, makes ultrasound-driven metal melt treatments a superior technique for the production of high-quality metal castings.

This video demonstrate the efficient degassing of viscous oil (40cP). Ultrasonication removes small suspended gas-bubbles from the liquid and reduces the level of dissolved gas below the natural equilibrium level.

Ultrasonic Inline Degassing & Defoaming of Oil (40cP)

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Ultrasonic booster and probe (cascatrode) mounted to the horn of the ultrasonic transducer UIP2000hdT

Ultrasonicator UIP2000hdT for heavy-duty applications such as metal melt degasification

High-Performance Ultrasonicators for Degassing Metal Melts

The degasification of metal melts such as aluminium alloys requires high-performance, high-power ultrasonic equipment. The ultrasonic probe must be specified for use with high temperatures and high viscosities. The ultrasonicator must be able to deliver and maintain constant amplitudes over long time periods. Hielscher Ultrasonics is specialised in the development, manufacturing and distribution of high-power ultrasound equipment for demanding applications such as the degasification of metal melts at high temperatures and under heavy duty. Supplying high-performance ultrasonicators at any scale and ultrasonic probes developed specifically for the treatment of liquid metals, Hielscher Ultrasonics is your partner for reliable and efficient metal melt processing.

Design, Manufacturing and Consulting – Quality Made in Germany

Hielscher ultrasonicators are well-known for their highest quality and design standards. Robustness and easy operation allow the smooth integration of our ultrasonicators into industrial facilities. Rough conditions and demanding environments are easily handled by Hielscher ultrasonicators.

Hielscher Ultrasonics is an ISO certified company and put special emphasis on high-performance ultrasonicators featuring state-of-the-art technology and user-friendliness. Of course, Hielscher ultrasonicators are CE compliant and meet the requirements of UL, CSA and RoHs.

The table below gives you an indication of the approximate processing capacity of our ultrasonicators:

Batch Volume Flow Rate Recommended Devices
0.5 to 1.5mL n.a. VialTweeter
1 to 500mL 10 to 200mL/min UP100H
10 to 2000mL 20 to 400mL/min UP200Ht, UP400St
0.1 to 20L 0.2 to 4L/min UIP2000hdT
10 to 100L 2 to 10L/min UIP4000hdT
15 to 150L 3 to 15L/min UIP6000hdT
n.a. 10 to 100L/min UIP16000
n.a. larger cluster of UIP16000

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Degassing and defoaming of liquids is an interesting application of ultrasonic devices. In this case the ultrasound removes dissolved CO2 from beer. Using Hielscher ultrasonic equipment you can degas or defoam liquids in beakers, tanks or inline (flow cell reactors).

Rapid Foaming Using Ultrasonics

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Literature / References

High performance ultrasonics! Hielscher's product range covers the full spectrum from the compact lab ultrasonicator over bench-top units to full-industrial ultrasonic systems.

Hielscher Ultrasonics manufactures high-performance ultrasonic homogenizers from lab to industrial size.

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