Abstract
Abstract Virtually all metals used industrially undergo a solidification process during their production. Depending on the material and its manufacturing process, its physical/mechanical properties are affected to a greater or lesser extent by the microstructure and microsegregation obtained during the phase change. Aluminum casting alloys are good examples of products where this microstructure is vital for obtaining the desired properties. A sequence of experiments to analyze the upward vertical unidirectional solidification with transient heat transfer conditions in Al-Si-Cu ternary alloys was developed in the present work. The experimental results obtained were compared with classical microsegregation models. Discrepancies related to their use for ternary alloys were raised. Since the calculated results by these models do not take into account the influence of one alloying element on the solubility of the other element, disparities were founded between experimental and numerical results. A microsegregation model was proposed based on the solubility limits of the Si in the alloy as a function of the Cu concentration present in the liquid. The model, combined with the concepts of classical microsegregation theory, allows a realistic description of the microsegregation phenomenon. The model showed an excellent agreement between microsegregation profiles of solute experimentally measured and calculated.
Highlights
Aluminum has been commercially produced for about 150 years and in this short time, its industry has expanded and is present in the world’s major poles
Microsegregation model based on the data obtained and its assumptions is proposed and, model predictions versus experimental data are presented and discussed
These cooling curves are similar to those presented by Sales et al.[30], one can see that temperature profiles decrease faster at positions closer to the mold bottom, and gradually dwindles toward completion of local solidification
Summary
Aluminum has been commercially produced for about 150 years and in this short time, its industry has expanded and is present in the world’s major poles. Studies have shown that the significant variables for solidification control are: solidification velocity (VS), thermal gradient ahead of the solid/liquid interface (TG), cooling rate (CR) and concentration and redistribution of solute, which are interconnected through constitutional supercooling[8]. These variables can be correlated with the microstructure obtained with the use of metallography techniques. Brody and Flemings[17] proposed a mathematical model to include the back-diffusion effects This solidification model assumes: 1) complete diffusion in the liquid phase and incomplete back-diffusion, 2) a plate-shaped dendrite geometry, 3) a constant diffusion coefficient, and 4) a linear or a parabolic solidification rate. An increase in Cu concentration in the liquid reduces the solubility of Si in the solid
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