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Fig. 3. The shorter the solidification time, the more refined the secondary dendrite arm spacing. 2 @


Procedure Within the Euro-


pean research project NADIA, which aims to promote the design


and manufacture 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 ex- posed to a T6 or T7 heat treatment. Temperature instruments placed at several locations on the castings


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recorded temperature profiles during filling, solidification and heat treat- ment. Additionally, sensors docu- mented the stress profile during heat treatment. Researchers performed microstructure analysis in the area of the 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 de- termine the conditions for air and water quenching. Secondary dendrite arm spac- ing is an important microstructure component after solidification, ac- cording to the authors. The shorter the solidification time, the more refined the microstructure (Fig. 3). The simulated values matched the measured ones well.


The simulated fraction of the


Si phase had a relatively con- stant value of approximately 0.4% evenly distributed throughout the part with some small, cooling condi- tion-dependent variations. The pore volume was in the range of 0.04% to 0.57% and at a 0.15mL/100g hydrogen content in the melt (prior to pouring). Measurements on the firing deck in


Mg2


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. Sept/Oct 2012 | METAL CASTING DESIGN & PURCHASING | 47


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