to 644F (340C) show distinc- tively lower values than for the mold preheated to 626F (330C). Tis is in acceptable agreement with prior experimental results in which hot tearing did not occur in molds preheated above 635F (335C). Tis is a good indication that
3
the strain rate can be used in simulations of real castings from AZ 91 magnesium alloy to predict possible hot tearing and in finding a solution as early as in the design phase. One can make a conjec- ture that the strain rate can be used as a predictor of hot tearing in magnesium alloys in general. Further work is required to prove this assertion. Te RDG criterion was used in
its differential form and viscos- ity was calculated to obtain the critical strain rate. Tis procedure needs further justification to be more rigorous. Nevertheless, the calculated limiting strain rate falls with the range that separates strain rates in the mold preheated to 626F and 644F (330C and 340C). Because the critical strain does not show physically realistic behavior near the solidus, its value should be determined at lower values of solid fraction. In conclusion, it is recom- mended that the critical strain rate is determined by combin- ing the “harp” casting tests, the simulation of the same tests and the set of Equations used in this study. Tis result can be used in
Results and Conclusions
Simulated strain rates
in the “harp” type casting with the mold preheated
simulations of real castings from that alloy to optimize process parameters to decrease the risk of hot tearing, or completely avoid it.
For more details, see the original version of this paper, 13-1340, published in the proceedings of the 2013 AFS Metalcast- ing Congress, at
www.afsinc.org.
ONLINE RESOURCE
Find the original research paper at
www.moderncasting.com
October 2014 MODERN CASTING | 41
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