“…The underlying reason behind such difference can be understood by comparing the atomic interaction between the solvent and solute, as indicated by the enthalpy of mixing, (Δ H ). 41 The predicted growth tendency of the α-Mg dendrite according to eq 9 in terms of the anisotropic parameters was in agreement with previous experimental findings. 13,22…”
Because of the existence of anisotropic surface energy with respect to the
hexagonal close-packed (hcp) lattice structure, magnesium alloy dendrite
prefers to grow along certain crystallographic directions and exhibits
a complex growth pattern. To disclose the underlying mechanism behind
the three-dimensional (3-D) growth pattern of magnesium alloy dendrite,
an anisotropy function was developed in light of the spherical harmonics
and experimental findings. Relevant atomistic simulations based on
density functional theory were then performed to determine the anisotropic
surface energy along different crystallographic directions, and the
corresponding anisotropic strength was quantified via the least-square
regression. Results of phase field simulations showed that the proposed
anisotropy function could satisfactorily describe the 3-D growth pattern
of the α-Mg dendrite observed in the experiments. Our investigations
shed great insight into understanding the pattern formation of the
hcp magnesium alloy dendrite at an atomic level.
“…The underlying reason behind such difference can be understood by comparing the atomic interaction between the solvent and solute, as indicated by the enthalpy of mixing, (Δ H ). 41 The predicted growth tendency of the α-Mg dendrite according to eq 9 in terms of the anisotropic parameters was in agreement with previous experimental findings. 13,22…”
Because of the existence of anisotropic surface energy with respect to the
hexagonal close-packed (hcp) lattice structure, magnesium alloy dendrite
prefers to grow along certain crystallographic directions and exhibits
a complex growth pattern. To disclose the underlying mechanism behind
the three-dimensional (3-D) growth pattern of magnesium alloy dendrite,
an anisotropy function was developed in light of the spherical harmonics
and experimental findings. Relevant atomistic simulations based on
density functional theory were then performed to determine the anisotropic
surface energy along different crystallographic directions, and the
corresponding anisotropic strength was quantified via the least-square
regression. Results of phase field simulations showed that the proposed
anisotropy function could satisfactorily describe the 3-D growth pattern
of the α-Mg dendrite observed in the experiments. Our investigations
shed great insight into understanding the pattern formation of the
hcp magnesium alloy dendrite at an atomic level.
“…Here, we employed and compared the anisotropy of surface energy, which is referred to the basal plane, to understand the dendritic orientation selection of different magnesium alloys 22 , 47 . Since the dendritic growth tendency or orientation selection is primarily determined by the thermodynamic factor related anisotropic surface energy in light of the underlying lattice structure 40 , 44 , 46 – 48 , in our atomistic model, instead of simulating the real solid/liquid phase transition in relation to growth kinetics during solidification, we assume a solid-vacuum interface and focus on equilibrium energy condition where the anisotropy of solid-liquid interface can be reflected by the solid-vapor interface based on the fundamental hcp lattice structure 28 , 39 , 49 . Figure 4 Schematic illustration for the correlation between the surface energy and the growth tendency or orientation selection of dendrite ( a ), the atomic structure of bulk magnesium with hexagonal symmetry ( b ), the ideal growth pattern of the α-Mg dendrite on the basal plane and non-basal planes, respectively ( c ), and the outer contour shape of the α-Mg dendrite at the stable state ( d ).…”
Section: Dendritic Morphology and Orientation Selection Of Binary Mg-mentioning
confidence: 99%
“…As revealed by the ab-initio calculations, the presence of the additional elements would cause lattice distortion of the magnesium matrix, degree of which can be evaluated by the c/a -ratio (see Fig. 5 ), based on the atomic size of both solvent and solute, and the atomic interactions reflected by the enthalpy of mixing (Δ H ) 48 , 50 . In theory, a large negative Δ H value implies a stronger atomic interaction between solvent and solute, and vice versa 51 .…”
Section: Surface Energy and Related Anisotropy Of Binary Mg-zn Alloysmentioning
Both synchrotron X-ray tomography and EBSD characterization revealed that the preferred growth directions of magnesium alloy dendrite change as the type and amount of solute elements. Such growth behavior was further investigated by evaluating the orientation-dependent surface energy and the subsequent crystallographic anisotropy via ab-initio calculations based on density functional theory and hcp lattice structure. It was found that for most binary magnesium alloys, the preferred growth direction of the α-Mg dendrite in the basal plane is always , and independent on either the type or concentration of the additional elements. In non-basal planes, however, the preferred growth direction is highly dependent on the solute concentration. In particular, for Mg-Al alloys, this direction changes from to as the Al-concentration increased, and for Mg-Zn alloys, this direction changes from to or as the Zn-content varied. Our results provide a better understanding on the dendritic orientation selection and morphology transition of magnesium alloys at the atomic level.
“…It is well known that the quality of cast products made of aluminum alloys is largely determined by their structure. In particular, the mechanical and operational properties of aluminum alloys significantly depend on such structural factors like morphology, size, and distribution of structural components, including grains of an aluminum α-solid solution and various primary crystallizing phases [1][2][3]. In this regard, the formation of a finegrained structure in castings is one of the ways to increase their properties and improve the quality of products from aluminum alloys [4][5][6].…”
The paper discusses the complex effect of melt overheating with subsequent fast cooling down to the pouring temperature on the crystallization process, microstructure and mechanical properties of Al-Mg-Si aluminum alloy. The results obtained facilitated the establishment of rational modes of melt overheating, leading to a significant change in the dispersion and morphology of structural components. In particular, with an increase in the melt overheating temperature to 900 °C with holding and subsequent rapid cooling to the casting temperature, a decrease in the average size of dendritic cells of the aluminum solid solution from 39 μm to 13 μm was observed. We also noticed the refinement of eutectic inclusions of the Mg2Si phase with compact morphology. An increased level of mechanical properties was noted; the maximum values of tensile strength and elongation reached 228 MPa and 5.24%, respectively, which exceeded the initial values by 22.5% and 52.3%, correspondingly. The microhardness of the aluminum solid solution sequentially increased from 38.21 to 56.5 HV with an increase in the temperature during melt overheating. According to the EDS linear scanning, an increase in the superheat temperature of the melt is accompanied by an increase in the degree of saturation of the solid solution with magnesium.
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