Special Die Casting Processes

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PGF 2019
Taschenbuch der GIESSEREI PRAXIS
Die Casting

Thixocasting

Special die casting process that utilises the thixotropic properties of partially liquid metal alloys. Suitable for aluminium and magnesium alloys with a large solidification interval:
GD-AlSi7Mg 19 °C temperature interval
MC-MgAl9Zn1 25 °C temperature interval

A prerequisite for the thixotropic behaviour of these alloys is the equiaxed formation of the a mixed crystals. In order to accomplish this, the solidifying melt is electromagnetically agitated during the external production of raw material for thixocasting, which breaks off the dendrite arms to create the equiaxed microstructure.

Prior to the casting process, such an externally produced extruded blank, corresponding to the mass of the casting, is inductively heated to the solidus – liquidus range with a melt proportion of about 30 to 40 %. Then the partially melted blank, which still acts like a solid, is transferred to the die casting machine’s shot sleeve and “cast” without turbulences trough the application of pressure by the plunger at a slow plunger speed. The effect of gravity significantly reduces the viscosity and the blank behaves like a highly viscous liquid. Reducing the speed of solidification makes thixocasting components highly dimensionally stable with a lower porosity than die-cast parts. These components also have a homogeneous microstructure with good mechanical properties.

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4 Pages

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