Ionic Liquids for immersion quenching of aluminium alloys

Tuesday, April 19, 2016: 4:50 PM
Ballroom DEF (Hyatt Regency Savannah)
Mr. Martin Beck , University of Rostock, Rostock, Germany
Mrs. Christin Neise , University of Rostock, Rostock, Germany
Dr. Michael Reich , University of Rostock, Rostock, Germany
Dr. Mathias Ahrenberg , University of Rostock, Rostock, Germany
Prof. Christoph Schick , University of Rostock, Rostock, Germany
Prof. Udo Kragl , University of Rostock, Rostock, Germany
Prof. Olaf Keßler , University of Rostock, Rostock, Germany
The manufacturing chain of metallic components consists of many process steps, whereas heat treatment is one of the most complex and important ones. Heat treatment often includes quenching which is commonly performed as immersion quenching in vaporising liquids. Unfortunately, this process is affected by the Leidenfrost-Effect, forming a vapour film at the component surface. The thermal insulation of the component caused by this vapour film lowers the cooling rate at the beginning of the quenching. Subsequently, the vapour film collapses locally at different times, leading to different cooling rates, which can generate residual stresses and distortion.

It’s common knowledge, that baths of molten salts and molten metals provide a quenching without any Leidenfrost-Effect. Nevertheless, they need to be operated at elevated bath temperatures combined with a considerable effort for cleaning the quenched components. In this work Ionic Liquids ,a new class of liquid quenching media, are investigated, showing nearly no Leidenfrost-Effect and can be used in baths at room temperature. These quenching media are salts with melting temperatures below 100 °C (often below room temperature). Therefore, these Ionic Liquids should be able to provide a fast and homogeneous cooling.

Aluminium and steel cylinders have been quenched in baths of different Ionic liquids with varying compositions and bath temperatures. The time-temperature curves have been recorded and the heat transfer coefficients were determined and compared to quenching in water. Some selected quenching experiments were recorded with a high speed video camera. It was shown, that the cooling power of Ionic Liquids could be significantly increased by water addition without any Leidenfrost-Effect. The results indicate a huge potential to homogenise immersion quenching.

Additional investigations on distortion of complex aluminium profiles quenched in ionic liquid and water have been carried out. The distortion measurements were compared to quenching simulations. Short time and long time thermal stability, costs, work safety and component cleaning of the new quenching media were also considered.

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