Ultrasonic assisted water quenching of aluminium and steel cylinders

Abstract

Quenching of metallic components during heat treatment is often done in liquid baths, because of its easy realisation and high mean quenching rates. The essential disadvantage of liquid quenching is the inhomogeneity, mainly caused by the heat isolating vapour film of the film boiling stage. The application of ultrasonic fields is one possibility to destabilise the vapour film and hence to lead to an accelerated and more homogeneous quenching step. The matter of this study is the cooling power characterisation of unidirectional ultrasonic assisted compared to conventional water quenching of austenitic steel 304 (X5CrNi18-10) and aluminium 6082 (AlSi1MgMn) cylinders. In this work, the ultrasonic amplitude, the size of the sound emitting surface (sonotrode) and the distance between sonotrode and sample as well as the water temperature were varied. Due to the ultrasound, the film boiling stage is influenced significantly, which leads to an increase in cooling rate in front of the sonotrode with an increasing ultrasonic amplitude, with an increasing size of the sound emitting surface and with a decreasing distance between sonotrode and sample. Unidirectional ultrasound causes a quenching homogenisation in the axial direction, but a dehomogenisation in the circumferential direction. Bidirectional ultrasound will be needed for quenching homogenisation also in circumferential direction.

Keywords:

• Ultrasonic assistance
• Water quenching
• Aluminium alloy
• Austenitic steel
• Heat transfer

The authors gratefully acknowledge funding of this work by Deutsche Forschungsgemeinschaft (grant no. KE616/14-1).