Papers by Keyword: Zener Drag

Abstract: Microstructural evolution during D.C. casting and subsequent homogenization of non-heat-treatable aluminium alloys involves complex phenomena, including micro-segregation of alloying elements and intermetallic phase selection during solidification as well as phase transformations of both primary (constituents - intergranular) and secondary (dispersoids - intragranular) intermetallic phases. In this study, we simulated the microstructural evolution of AA3003 using a CALPHAD-based modelling framework implemented in ThermoCalc®. The framework integrates a Scheil-Gulliver solidification model coupled with a 1-D micro-segregation alleviation and diffusional phase transformation model (DICTRA®) and a Kampmann-Wagner Numerical (KWN) model for dispersoid precipitation (TC-PRISMA®). According to this approach, the development of a robust computational methodology is aimed at accurately predicting the influence of homogenization cycles on dispersoid precipitation, which in turn affects recrystallization behaviour via the well-known Smith-Zener drag phenomenon. Additionally, these CALPHAD-based simulations facilitate the assessment of impurity content effects on dispersoid precipitation, considering the increasing use of scrap in the fabrication of non-heat-treatable aluminium alloys. Furthermore, they provide precise estimates of Smith-Zener pinning forces as inputs for downstream mesoscale full-field process models, contributing to a holistic through-process modelling approach.

Abstract: Recrystallization is a major means for controlling the grain size of steel during hot deformation. Usually, small grain sizes deliver superior mechanical properties. To aid the grain size controlling effect of recrystallization, small precipitates of carbo-nitride particles can be utilized to hinder the movement of grain boundaries. Interestingly, these particles are not only effective during grain growth, but also during recrystallization. In the present work, a recently developed state-parameter based model is introduced that is capable of describing both, the individual processes of static recrystallization, dynamic and static recovery and precipitation as well as the mutual interaction of these mechanisms in the course of elevated temperature processing. The evolution of state parameters within the model is discussed and the simulation results are compared to experimental information. Within our approach, a vast amount of experimental data for microalloyed steel is reproduced on basis of a single set of input parameters

Abstract: During reversible break-down hot rolling, recrystallization can take place during inter-pass annealing and even after the final pass, because the material is kept at high temperature throughout the process. A partially recrystallized microstructure is quite often obtained during inter-pass annealing and is the starting state for the subsequent rolling pass. This is in particular the case when fine particles are already present or have just precipitated in the microstructure. The particles can pin the moving grain boundaries in the hot deformed material with low energy stored during deformation. To transfer the partly recrystallized microstructure from the recrystallization model to the deformation model for simulation of the subsequent pass, a new link method has been developed for multi-pass through-process modeling. This method allows a direct data flow between the deformation model GIA-3IVM+ and the recrystallization model CORe. This new model framework was used to simulate the microstructure evolution during break-down hot rolling of precipitates containing alloy AA6016. The predicted microstructure agrees well with experimental observations.

Abstract: The physical basis and a mathematical formulation of a softening model nicknamed Alsoft, accounting for the combined effect of recovery and recrystallization during annealing of heavily deformed aluminium alloys have been presented. The prediction power of the model is tested against experiments in terms of softening kinetics and final grain structure of selected Al-Mn-Fe-Si-model alloys with different as homogenized microchemistries in terms solid solution levels of Mn (potential of concurrent precipitation) and different constituent particle and dispersoid structures. It is demonstrated that good model predictions may be obtained for alloys and conditions which are not or too a limited extent influenced by particle drag effects and concurrent precipitation while conditions strongly affected by these effects are increasingly difficult to model and in the most extreme cases impossible with reasonable input model parameters.

Abstract: Grain growth processes in real polycrystalline materials are mostly characterized by the presence of restraining forces, originating, among others, from second phase particles dispersion (Zener drag) or solute atoms segregating at the grain boundaries (solute drag). Both the restraining mechanisms were introduced in the framework of the statistical theory of grain growth, showing their peculiar effects on kinetics and on grain size distribution evolution [1,2,. The present work moves from the previous results and gives a further clarification of pseudo-steady state kinetics occurring under particular solute drag inhibition intensity and will discuss it in comparison with grain growth stagnation conditions produced by Zener drag. In case of second phase particle inhibiting grain growth, the normal case in real systems is the time and temperature dependence of the inhibition intensity due to the evolution of precipitates (e.g. Ostwald ripening. Such evolutions of inhibition, which typically drops with increasing temperature, can cause microstructure instabilities like abnormal grain growth or secondary recrystallization. It is thus introduced in the model a time-temperature depending inhibition drop, which influences both kinetics and grain size distribution evolution. Conditions for the onset of particular effects like abnormal grain growth are assessed and discussed.

Abstract: Control of grain size during recrystallization of aluminum alloys is critical when tailoring material properties for structural applications. Most commonly the grain size is controlled by adding alloying elements which form second phases during homogenization heat treatments small enough to impose a Zener drag on the grain boundary mobility. These phases are known as dispersoids and are in the 10 to 200 nm in diameter range. In Al-Zn alloys, zirconium has been successfully used in controlling the degree of recrystallization after solution heat treatments. It is commonly understood that the Al3Zr dispersoids of about 20 nm in diameter present in the microstructure are the key features affecting grain boundary mobility. With the success of controlling recrystallization in Al- Zn alloys, zirconium has been added to other alloy systems, such as Al-Cu-Mn, and a similar retarding effect in recrystallization kinetics has been observed as seen in the Al-Zn systems. However, in Al-Cu-Mn alloys, zirconium bearing dispersoids are not observable in the microstructure. Consequently, additional microstructural effects such as solute drag need to be considered to explain the experimental observations. In this paper, the role of zirconium additions in aluminum alloys will be summarized.