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Fig. 5. Peak yield strength of the cylinder head was achieved after about one hour and did not change significantly after 140 minutes of aging.


3


Results and Conclusions


Simulation numbers


for the concentration of magnesium in a cylin-


der head after solution treatment at 936F (530C) for 240 minutes cor- related with previously established research (Fig. 4). Quench rates of the part exposed to a 150F (60C)


water quench bath were around 122F/second (50C/second) for its outer areas and 50F/second (10C/ second) for the inner areas. Accord- ing to the authors, due to the ideal test conditions, the maximum value is considerably higher than what could be achieved in a production environment, when many castings are quenched together in a basket.


Measurements for yield strength after


aging found values around 260 MPa in the outer areas, which were in good correlation with the simulation. However, the simulated values for the interior of the part were about 25MPa below the measured values. Te peak yield strength of the part


was achieved at approximately the same time as simulated—about one hour— and did not change much after 140 minutes of aging (Fig. 5). Te research- ers found the simulated distribution of the yield strength shows the quench- ing process has the biggest impact on this value, and casting geometry and its orientation during quenching are the most important parameters. Te measurements show a smaller variation in the yield strength as a function of its location than was simulated. Overall, the results of the cylin-


der head tests showed the as-cast microstructure, including phase and porosity distribution and mechanical properties after heat treatment, can be predicted. Te models can be used to evaluate and optimize alloy compo- sition and process parameters with metallurgical relevance. By predicting local mechanical


properties, designers and metalcast- ers can optimize the casting and heat treatment processes and part geometry. The simulation results can be used in lifetime optimization tools to evaluate thermomechani- cal fatigue in areas exposed to high thermal load conditions. 


Te paper (12-028) on which this article is based was first presented at the 2012 American Foundry Society Metalcasting Congress in Columbus, Ohio.


48 | METAL CASTING DESIGN & PURCHASING | Sept/Oct 2012


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