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Fig. 3. The shorter the solidification time, the more refined the secondary dendrite arm spacing.


ture of automotive components in lightweight alloys, a cylinder head was poured using several melt compositions, cooling conditions and degrees of porosity (Fig. 2). The castings then were exposed to a T6 or T7 heat treatment. Tempera- ture instruments placed at several locations on the castings recorded temperature profiles during filling, solidification and heat treatment. Additionally, sensors documented the stress profile during heat treat- ment. Researchers performed micro- structure analysis in the area of the


2


Procedure Within the European


research project NADIA, which aims to promote the design and manufac-


firing deck of the cylinder head. The measured temperature


profiles were used to calibrate the boundary conditions in the simula- tion software for all process steps, partially by using inverse optimiza- tion technology to correctly deter- mine the conditions for air and water quenching. Secondary dendrite arm spacing is an important microstructure com- ponent after solidification, accord- ing to the authors. The shorter the solidification time, the more refined the microstructure (Fig. 3). The sim- ulated values matched the measured ones well. The simulated fraction of


the Mg2Si phase had a relatively constant value of approximately


0.4% evenly distributed throughout the part with some small, cooling condition-dependent variations. The pore volume was in the range of 0.04% to 0.57% and at a hydrogen content in the melt (prior to pour- ing) of 0.15ml/100g. Measurements on the firing deck in


areas impacted by the effect of cooling channels found values around 0.12% pore volume. The simulation of the heat treat-


ment provides the degree of dissolu- tion as a result of the solution treat- ment, which can be used to evaluate whether its duration and tempera- ture were sufficient to dissolve the copper and magnesium. Addition- ally, the concentrations of copper and magnesium were predicted.


Fig. 4. The predicted magnesium concentration after solution treatment (left) and local quenching rate correlated with actual measurements. 36 | MODERN CASTING September 2012


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