A COUPLED THERMOMECHANICAL, THERMAL TRANSPORT AND SEGREGATION ANALYSIS OF THE SOLIDIFICATION OF ALUMINUM ALLOYS ON MOLDS OF UNEVEN TOPOGRAPHIES

摘要

A coupled thermomechanical, thermal transport and segregation analysis of aluminum alloys solidifying on uneven surfaces is presented. The uneven surfaces are modelled as sinusoids with different wavelengths and amplitudes. Phenomena occurring during early stages of solidification play an important role in the formation of surface defects. At the mold-metal interface, formation of air-gaps leads to variations in heat flux from the solidifying shell to the mold. The heat flux is either determined from the contact pressure during perfect contact or through air-gap sizes during imperfect contact (air-gap nucleation). The effects of inverse segregation, arising from shrinkage driven flow in the melt, on nucleation of air-gaps and evolution of stresses in the solidifying shell are examined. The present finite element based numerical model consists of a volume-averaged solidification model coupled with an elasto-viscoplastic deformation model in the solidifying shell with air-gap nucleation and imperfect contact at the metal-mold interface. For different sinusoidal topographies, a particular wavelength that leads to reduction in equivalent stresses and growth front morphology unevenness, in the evolving solid shell, is sought for different aluminum alloys. The current analysis will be extended to include the effects of mold coatings and surface roughness of molds on air-gap formation and stress development.