Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

LKR Numerical CALPHAD Approach of Aluminium 2024 Alloy in the semi-solid region.(Prediction of Semi-Solid Temperature at a given composition)

When casting alloys in the semi-solid state with the New Rheocasting Process, usually a 50% solid fraction is located. Up to now, for each alloy a special temperature is given, at which the casting will take place, for instance about 580°C for A356, one of the most common alloys. For semi-solid casting it is very important that in the semi-solid range the alloy has a high tolerance in temperature – so that for 1°C change the solid fraction changes just minimally, which is 1% for A356. However, with other alloys, the temperature tolerance is much lower, so that 1°C change produces up to 4% change in solid fraction. The New Rheocasting Process has a stability of about ±1,5 to 2°C, which would mean a change of maximal ±8% of solid. This would still work. However every alloy has a tolerance in its composition. But a change in element content changes also the solidification curve, as can be seen in the technical report. So it would mean that one casts at 65% solid while thinking of 50% solid fraction and therefore produces bad parts.

An awareness of high tolerance intervals in alloys that change semi-solid temperature of given alloy with different composition makes one think of how to know the exact semi-solid temperature in order to ensure secure high-quality casting. There are expensive programs like Thermocalc or JMatPro that can do that, but this takes time and costs money. LKR now made numerical approximations based on the calphad approach for the alloys 2024, 356, 357 (Aluminium) and AM50 to AZ91 (Magnesium with Al, Mn, Zn Elements) in order to provide the cast shop with the necessary information.

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