A Thermodynamic Study on the Effect of Solute on the Nucleation Driving Force, Solid–Liquid Interfacial Energy, and Grain Refinement of Al Alloys

Abstract

Chemical composition is known to have significant effects on the grain refinement behavior of inoculated Al alloys during solidification. In this study, the influences of solute contents on the thermodynamic nucleation driving force and solid-liquid interfacial energy of binary Al alloys have been studied by CALPHAD method. The solute effect on the nucleation barrier and nucleation rate, thus on the grain refinement of Al alloys both with and without high potency nucleation particles, was analyzed based on the classical heterogeneous nucleation theory and free growth concept. Based on the classical heterogeneous nucleation theory, the calculation results reveal that Si has the effect of increasing the nucleation barrier of heterogeneous nucleation of grains and thus reduce the nucleation rate significantly. Alloying elements Cu and Mg have the effect of promoting heterogeneous nucleation and grain refinement. However, peritectic forming elements, e.g., Ti, Zr, V, have only negligible effects on the nucleation barrier. For solidification of Al alloys inoculated with high potency nucleation particles, the effect of nucleation driving force caused by different solute elements on the grain size of inoculated aluminum alloys has been quantitatively studied by a grain size prediction model for isothermal melt solidification. It is revealed that the solute dependent Gibbs-Thompson coefficients of Al-Cu, Al-Mg and Al-Si alloys have the influence of promoting the grain refinement by reducing the free growth undercooling.

Microstructures and tensile properties of as-cast Mg-5Sn-1Si magnesium alloy modified with trace elements of Y, Bi, Sb and Sr

“…It is now generally accepted that solute undercooling (ΔT) during solidification process and solute segregation [(quantified by the growth restriction factor (GRF)] [34] are critical in determining the final grain size and distribution of the second phase of as-cast magnesium alloys. In order to describe the impact of ΔT on as-cast grain size, a correlative growth restriction factor (GRF) or Q value is widely used.…”

Ultrasound cavitation induced nucleation in metal solidification: An analytical model and validation by real-time experiments

“…I nuc is calculated by [28] , [29] : where k is the Boltzmann constant; I 0 = nkT/h ; n is the atom number per unit volume, h is Plank constant; ΔG*(T) is the energy barrier for the formation of a critical nucleus, given by: where T m is the melting temperature; ΔH is the enthalpy of phase change; V mol is the molar volume of the solid phase; σ sl is the solid–liquid interfacial energy. These parameters are normally constants at atmospheric pressure but considered as pressure-dependent in this research.…”

“…The θ is influenced by many factors, such as substrate type and property, solid–liquid interfacial energy. Generally, the value is treated as a constant, independent of solute content as did in the work of [29] , [33] , [34] . In the present work, the wetting angle is simply considered as an angle between alumina and aluminum melt It is a relatively constant value of 86° at different temperatures for the polycrystalline aluminum with a surface roughness of 720 Å [35] .…”

Understanding the refinement of grains in laser surface remelted Al–Cu alloys

“…The well-studied Al-Cu system [25][26][27][28] is used in conjunction with a commonly used Al-Ti-B grain refiner addition to study the effect of solute and potency of grain refiner particles on the grain size. Al-Ti-B provides 1) a strong thermodynamic driving force for solidification due to the high solute partitioning of Ti which rapidly produces constitutional supercooling [29] and 2) TiB2 particles, which are very effective substrates for nucleating the α-Al phase due to the very good lattice matching between the substrates and pure Al [30] probably with an intermediate layer [31,32].…”