Thermal-Microstructural Analysis of Anodic and Electrolytic Copper Solidification: Simulation and Experimental Validation JORGE SEBASTIA ´ N ROMERO, DIEGO JAVIER CELENTANO, and MARCELA ANDREA CRUCHAGA This work analyzes the solidification process of anodic and electrolytic copper. The aim of this study is to perform an experimental validation of numerical results computed using a proposed thermal formulation including microstructural evolution. To this end, a set of experiments is carried out testing primary and eutectic phase formation in copper. To evaluate the formation of different microstructural phases, anodic copper (99.80 pct purity, approximately) and elec- trolytic copper (99.99 pct purity, approximately) are used. Primary and eutectic phases evolve in anodic copper; meanwhile, only a primary phase is obtained in electrolytic copper. The effect of heat extraction conditions is evaluated using sand, graphite, and steel molds to promote dif- ferent cooling rates. The proposed microstructural model takes into account nucleation and grain growth laws based on thermal undercooling together with microstructural evolution. The primary copper evolution model is based on solute diffusion at the grain scale and on the dendrite top-growing kinetic; meanwhile, the eutectic evolution is assumed proportional to the copper initial composition and eutectic undercooling. The corresponding numerical formulation is solved in the framework of the finite-element method. Finally, the computed temperature histories and final values for the grain density and radius, including primary or dendritic phase and eutectic solid volumetric fractions, are all compared and validated with the experimental measurements. DOI: 10.1007/s11663-011-9483-8 Ó The Minerals, Metals & Materials Society and ASM International 2011 I. INTRODUCTION THE main impurity present in anodic and electrolytic copper is oxygen. In particular, for anodic copper, there are also some traces of sulfur, lead, iron, and noble metals. During electrorefining processes, copper oxides (Cu 2 O) present in anodic copper are dissolved or leached into the electrolyte without using any external driving force, whereas pure copper is dissolved because of the voltage difference and electrical current applied. Moreover, dissolution rates and the energy involved for electrorefining processes, as well as the tendency for passivation, are different for each grain size. Because of the lower electrochemical crystallization overvoltage, dissolution occurs preferentially at the copper grain boundaries and is always more intense around impuri- ties or inclusions. [1] This is the reason why the grain size and impurities distributions have an influence on anodic dissolution, i.e., anodes with finer grains are dissolved more rapidly because of their higher content of grain boundaries. However, anodes with finer grains are more suscep- tible to passivation. Therefore, regarding to a uniform passivation, a relatively coarse and equiaxed structure is desirable. [2,3] For these reasons, it is important to know the microstructural features obtained in the previous castings so that engineers can do an accurate calculus of the electricity needed to dissolve the pure copper and do not overfeed the system unnecessarily, implying a change in currents lines inside the electro- lyte and causing an irregular growing front on the copper cathode. In a copper alloy, as the temperature of the melt decreases below the liquidus temperature, primary copper is formed. Then, eutectic is developed when the eutectic temperature is reached. The primary copper and the eutectic solid volumetric fractions can be obtained through respective evolution models. Although fundamental advances have been made toward a complete theoretical solution of the micro- structural formation in castings, the description of different aspects, such as primary and secondary arm spacings, is still unsatisfactory. An exhaustive and complete review of different approaches describing all the mechanisms involved in the microstructural formation, separately reported for primary and eutectic alloys, can be found in References 4 through 8. Regarding to the modeling of copper solidification processes, most formulations were aimed JORGE SEBASTIA ´ N ROMERO, Postgraduate Student, is with the Departamento de Ingenierı´a Metalu´ rgica, Universidad de Santiago de Chile, 9170022 Santiago, Chile. Contact e-mail: jorgerom_met@ yahoo.com MARCELA ANDREA CRUCHAGA, Professor, is with the Departamento de Ingenierı´a Meca´ nica, Universidad de Santiago de Chile. DIEGO JAVIER CELENTANO, Professor, is with the Departamento de Ingenierı´a Meca´ nica y Metalu´rgica, Pontificia Universidad Cato´lica de Chile, 7820436 Santiago, Chile. Manuscript submitted October 16, 2010. METALLURGICAL AND MATERIALS TRANSACTIONS B