Combined thermal, solutal and momentum transport. Assume a rigid mold.

1. Surface defects in casting Sub-surface liquation Crack formation Ripple formation Uneven mold surface topography effects Undesirable growth using plain mold Desirable growth using uneven mold Mold Phase change and mushy zone evolution Heat transfer Solute transport Casting domain Fluid flow Deformable or non-deformable mold Heat transfer Contact pressure/ air gap criterion Inelastic deformation Design of mold surface topography during early stage solidification of Al alloys Cornell University College of Engineering Sibley school of Mechanical and Aerospace Engineering PI: Prof. Nicholas Zabaras Participating students: Deep Samanta, Lijian Tan Material Process Design and Control Laboratory Surface tension effects Mold topography Surface energy Gravity Initial contact between mold and liquid The size of micro-gap Heat flux at early stages of solidification Low solid fractions usually accompanied by melt feeding. With increase in solid fraction, there is an increase in strength and bonding ability of dendrites. Surface quality of aluminum casting Macro-scale effects • Combined thermal, solutal • and momentum transport. • Assume a rigid mold. • Imperfect contact and air gap • formation at metal/mold interface Parametric analysis for the following parameters: 1) Wavelength(λ) 2) Concentration (CCu) 3) Superheat (ΔTmelt) λ = 5 mm Modeling effects of uneven mold surface on solidification Equivalent stress (t = 0.1 s) Isotherms (t = 0.1s) Micro-scale effects λ = 3 mm A change of surface tension drastically changes the solidification speed at very early stages of solidification. Gap nucleation time (comparison with analytical study) Selected publications • Heat transfer in the mold, solid shell and melt. • Heat transfer causes deformation (thermal stress). • Gaps or contact pressure affect heat transfer. • Solidification after air-gap nucleation not modeled. D. Samanta and N. Zabaras, “A coupled thermomechanical, thermal transport and segregation analysis of the solidification of Aluminum alloys on molds of uneven topographies ”, Materials Science and Engineering: A, in press. Lijian Tan, Nicholas Zabaras, “A thermomechanical study of the effects of mold topography on the solidification of Aluminum alloys", Materials Science and Engineering: A, Vol. 404, 197-207, 2005. D. Samanta and N. Zabaras, “Numerical study of macrosegregation in Aluminum alloys solidifying on uneven surfaces”, International Journal of Heat and Mass Transfer, Vol. 48, 4541-4556, 2005. L. Tan, D. Samanta and N. Zabaras, “A coupled thermomechanical, thermal transport and segregation analysis of the solidification of aluminum alloys on molds of uneven surface topographies”, Proceedings of the 3rd M.I.T. Conference on Computational Fluid and Solid Mechanics, Massachusetts Institute of Technology, Cambridge, MA, June, 2005 . Al-Cu alloy with 1.8% Cu is most susceptible to hot tearing Wavelength less than 5mm corresponds to an optimum Left: Evolution of pressure at troughwith time at selected wavelengths. Right: Mean shell thickness at gap nucleation time.