Modeling the Behavior of a Type-319 Aluminum Alloy During Quenching

131 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2002.Desired weight savings in automobiles has led to an increase in the use of cast aluminum parts in engine applications. To achieve the strength required in these applications, parts must be heat treated prior to service. This heat treatment involves a severe quench that can cause large thermal gradients, leading to undesirable residual stresses and strains. The ability to predict accurately residual stress and strain development during the quench would allow the design of aluminum engine parts with increased fatigue resistance and higher geometric tolerances. In this work, the behavior of a type-319 cast aluminum alloy (W319) is studied, from the equilibrium solid-solution state, to the end of the quench. A mechanical threshold stress model is used to predict the onset of plastic deformation in quenched parts due to effects of temperature and strain rate. The evolution of this mechanical threshold follows a Voce Law formulation. Parameters of the model are derived from rapid, uniaxial tension tests conducted on samples cast in green sand. The model is used in a one-dimensional, semi-analytical solution to predict the deformation and residual stress of side-quenched aluminum beams of uniform cross section. The model is also applied in full three-dimensional form to predict the behavior of beams of a non-uniform cross section. Model results are compared to results of quenching experiments performed on cast aluminum beams, including both transient deformation measurements and residual stress measurements obtained by a layer-removal technique. It is found that residual stress is predicted reasonably well by the model and that the model converges acceptably quickly to a solution when applied in a three-dimensional finite-element analysis. Transient and residual deformation are found to be more difficult to predict than residual stress.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD