Sensitivity of Thermophysical Material Properties on Solidification Simulation of Al-Si Binary Alloys
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l) alloys are finding newer applications everyday due to their attractively high strength to weight ratio, which enables production of low weight parts with high mechanical strength. An increased demand of the use of Al alloys in a variety of applications ranging from common household products to the technologically challenging automotive and aerospace components has warranted a more thorough understanding of their solidification characteristics.[4] In our earlier work,[4] we presented a new numerical algorithm that enables the inclusion of the undercooling of liquidus temperature prior to the solidification event, DT, in the solidification simulation. Further, this algorithm also enables a more robust formulation for the evaluation of the liquid fraction in the mushy zone (region where liquid and solid phases coexist during solidification of binary alloys) and further saves nearly half the computing cost. The numerical algorithm forms an important component in the success of the solidification simulation. Another critical component is the data for material properties applied for the liquid and solid phases used in the simulation. All solidification simulations carried out thus far have not paid much attention to the sensitivity HONGDA WANG, Postdoctoral Candidate, and SUMANTH SHANKAR, Associate Professor, are with the Department of Mechanical Engineering, McMaster University, Hamilton, ON L8S 4L7, Canada. MOHAMED S. HAMED, Associate Professor, is with Thermal Processing Laboratory (TPL), McMaster University. Contact e-mail: [email protected] Manuscript submitted July 6, 2010. Article published online February 25, 2011 2346—VOLUME 42A, AUGUST 2011
of the numerical results of solidification simulations such as transient G, R, cooling rate (GÆR), and solidification start time on the thermophysical material properties assumed in the model. Specifically, there was no study to analyze the effectiveness of assuming material properties such as thermal conductivity, specific heat capacity, density, and solute diffusivity for both the solid and liquid phases as constants in the numerical model. A major hurdle to such study is the availability of a numerical model that is validated by experimental results. This hurdle was successfully scaled in this study by obtaining a valid numerical model mainly due to the development of a new algorithm, which included the effect of DT,[4] a critical phenomenon during solidification. In this study, simulations were carried out to evaluate the effect of considering these material properties as constants on the resultant solidification parameters such as transient temperature distribution during solidification and solidification start times (location of the liquidmushy zone interface (dendrite tip) during solidification). The simulation was set up to duplicate the experimental conditions of Reference 5 wherein upward solidification (velocity of liquid/mushy zone interface is against the direction of the gravity vector) of Al-3 wt pct Si alloy was carried out. The fluid flow in this case was entirely caused by sol
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