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 concentra-
tion of magnesium in a cylinder head after solution treatment at 936F (530C) for 240 minutes correlated 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 the casting’s 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. The 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). The researchers found the simulated distribution of the yield strength shows the quenching process has the biggest impact on this value, and casting geometry and its orientation during quenching are the most important parameters. The measurements show a smaller variation in the yield strength as a function of its location than was simulated. Overall, the results of the cylinder head tests showed
the as-cast microstructure, including phase and poros- ity distribution and mechanical properties after heat treatment, can be predicted. The models can be used to evaluate and optimize alloy composition and process parameters with metallurgical relevance.
By predicting local mechanical properties, designers and metalcasters can optimize the casting and heat treat- ment processes and part geometry. The simulation results can be used in lifetime optimization tools to evaluate thermomechanical 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.
ONLINE RESOURCE
To read the full paper on which this article was based, visit
www.moderncasting.com.
September 2012 MODERN CASTING | 37
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