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A cellular automaton-finite difference-lattice Boltzmann (CA-FD-LB) model, coupled with the calculation of ternary alloy thermodynamics, has been applied for the simulations of welding porosity formation and dendritic solidification during welding of 6xxx aluminum alloys (Al-Mg-Si). It is revealed that the nucleation and growth of the welding pores occur in the interdendritic space, and that the pores are squeezed into irregular shapes by the growing dendrites. During the solidification of the weld pool, the porosity percentage and welding pore number continuously increase. The effects of the heat input on the welding pore formation and dendrite growth have been investigated. The results indicate that, with the heat input decreasing, the dendrite arms become finer, while the percentage of porosity decreases and the gas pore numbers increase. This work not only reproduces the welding porosity formation of 6xxx aluminum alloys but also guides the prediction of the microstructure of the welded joints.

The interdependence between structural mechanics and microstructure solidification is an inherently three-dimensional phenomenon, where the complex physical processes and mechanical interactions can lead to dendrites growing at orientations influenced by twisting and out of plane bending. These effects can have a significant impact on the formation of defects and the overall macroscopic material properties of the structure. However, all attempts to numerically model this process so far have been limited to two-dimensional representations of the problem, which necessitates ignoring any potential behaviour that may arise from these more complex deformation events. For this reason, the two-dimensional numerical methods presented in previous papers, which couple a Finite Volume Structural Mechanics Solver to a Cellular Automata solidification solver, have been expanded so that problems may now be simulated in three dimensions. Results are presented which do not aim to predict any specific mechanism but rather highlight the new capabilities of this improved three-dimensional modelling framework.

In this paper, an analytical method previously proposed for one-phase and two-phases transient mass/heat diffusion with reaction is now applied to derive closed-form solutions for the inward transient solidification of cylinders and spheres, considering a global metal/mold heat transfer coefficient. Furthermore, temperature profiles are derived for mold, solid, and liquid phases. The analytical model developed proved to be general, thus permitting to derive closed-form exact analytical solutions for pure metals and eutectics.

Additive manufacturing, often known as three-dimensional (3D) printing, is a process in which a part is built layer-by-layer and is a promising approach for creating components close to their final (net) shape. This process is challenging the dominance of conventional manufacturing processes for products with high complexity and low material waste 1 . Titanium alloys made by additive manufacturing have been used in applications in various industries. However, the intrinsic high cooling rates and high thermal gradient of the fusion-based metal additive manufacturing process often leads to a very fine microstructure and a tendency towards almost exclusively columnar grains, particularly in titanium-based alloys 1 . (Columnar grains in additively manufactured titanium components can result in anisotropic mechanical properties and are therefore undesirable 2 .) Attempts to optimize the processing parameters of additive manufacturing have shown that it is difficult to alter the conditions to promote equiaxed growth of titanium grains 3 . In contrast with other common engineering alloys such as aluminium, there is no commercial grain refiner for titanium that is able to effectively refine the microstructure. To address this challenge, here we report on the development of titanium–copper alloys that have a high constitutional supercooling capacity as a result of partitioning of the alloying element during solidification, which can override the negative effect of a high thermal gradient in the laser-melted region during additive manufacturing. Without any special process control or additional treatment, our as-printed titanium–copper alloy specimens have a fully equiaxed fine-grained microstructure. They also display promising mechanical properties, such as high yield strength and uniform elongation, compared to conventional alloys under similar processing conditions, owing to the formation of an ultrafine eutectoid microstructure that appears as a result of exploiting the high cooling rates and multiple thermal cycles of the manufacturing process. We anticipate that this approach will be applicable to other eutectoid-forming alloy systems, and that it will have applications in the aerospace and biomedical industries. Titanium–copper alloys with fully equiaxed grains and a fine microstructure are realized via an additive manufacturing process that exploits high cooling rates and multiple thermal cycles.

The nascent field of nanotechnology-enabled metallurgy has great potential. However, the role of eutectic alloys and the nature of alloy solidification in this field are still largely unknown. To demonstrate one of the promises of liquid metals in the field, we explore a model system of catalytically active Bi-Sn nano-alloys produced using a liquid-phase ultrasonication technique and investigate their phase separation, surface oxidation, and nucleation. The Bi-Sn ratio determines the grain boundary properties and the emergence of dislocations within the nano-alloys. The eutectic system gives rise to the smallest grain dimensions among all Bi-Sn ratios along with more pronounced dislocation formation within the nano-alloys. Using electrochemical CO 2 reduction and photocatalysis, we demonstrate that the structural peculiarity of the eutectic nano-alloys offers the highest catalytic activity in comparison with their non-eutectic counterparts. The fundamentals of nano-alloy formation revealed here may establish the groundwork for creating bimetallic and multimetallic nano-alloys. The combination of metallurgy concepts and nanotechnology with liquid metal processing has been largely unexplored. Here the authors use liquid-phase ultrasonication to produce a model system of catalytically active nano-alloys, demonstrating electrocatalysis and photocatalysis.

The Interdependence model is now widely used to analyze the results of grain refinement studies. Although the model was developed to predict the grain size of an alloy cast under the assumptions of near equilibrium solidification and the presence of potent nucleant particles, it has been found to be applicable to a wide variety of alloys, casting methods, and cooling conditions. However, the strength of the Interdependence model is when it is used as a diagnostic tool that can reveal the mechanisms influencing the refinement of alloys under particular solidification conditions. This paper presents an introduction to the Interdependence model, its recent validation by experiment, and examples of how it can be applied to the solidification of alloys during additive manufacturing. For example, the model explains the difficulties in promoting a transition from columnar to equiaxed grains during additive manufacturing while also providing insights into how a fully equiaxed grain structure can be achieved.

The L ↔ Al + Al11Ce3 technologically important eutectic transformation in Al–Ce binary alloys, containing from 5 to 20 wt.% Ce and ranging from hypo- to hypereutectic compositions, was examined along with the microstructure and properties of its solidified product. A combination of thermal analysis and metallography determined the coordinates of the eutectic point at 644.5 ± 0.6 °C and 10.6 wt.% Ce, clarifying the existing literature ambiguity. Despite the high entropy of melting of the Al11Ce3 phase, in hypoeutectic alloys the eutectic was dominated by the regular morphology of periodically arranged lamellae, typical for non-faceted systems. In the lamellar eutectic, however, the faceting of Al11Ce3 was identified at the atomic scale. In contrast, for hypereutectic compositions, the Al11Ce3 eutectic phase exhibited complex morphology, influenced by the proeutectic Al11Ce3 phase. The Al11Ce3 eutectic phase lost its coherency with Al; it was deduced that a partial coherency was present only at early stages of lamellae growth. The orientation relationships between the Al11Ce3 and Al in the eutectic structure, leading to partial coherency, were determined to be [0 0 1]Al ║ [1¯ 1 1]Al11Ce3 with (0 4 4¯)Al ║ (2¯ 0 0)Al11Ce3 and [0 1 1]Al ║ [3¯ 0 1]Al11Ce3 with (2¯ 0 0)Al ║ (0 6 0)Al11Ce3. The Al11Ce3 phase with a hardness of 350 HV and Al matrix having 35 HV in their eutectic arrangement formed in situ composite, with the former playing a role of reinforcement. However, the coarse and mostly incoherent Al11Ce3 eutectic phase provided limited strengthening and the Al–Ce alloy consisting of 100% eutectic reached at room temperature a yield stress of just about 70 MPa.

Rapid movement of the melt pool (at a speed around 1 m/s) in selective laser melting of metal powder directly implies rapid solidification. In this work, the length scale of the as-built microstructure of parts built with the alloy AlSi10Mg was measured and compared with the well-known relationship between cell size and cooling rate. Cooling rates during solidification were estimated using the Rosenthal equation. It was found that the solidification structure is the expected cellular combination of silicon with α-aluminum. The dependence of measured cell spacing on calculated cooling rate follows the well-established relationship for aluminum alloys. The implication is that cell spacing can be manipulated by changing the heat input. Microscopy of polished sections through particles of the metal powder used to build the parts showed that the particles have a dendritic-eutectic structure; the dendrite arm spacings in metal powder particles of different diameters were measured and also agree with literature correlations, showing the expected increase in secondary dendrite arm spacing with increasing particle diameter.

Rare earth elements and transition elements are widely used in aluminum alloys, magnesium alloys and copper alloys due to their unique microalloying effects. With regard to in-depth research on the grain refinement characteristics of rare earth elements and transition elements, the combination of grain refinement and microalloying in the master alloys has a great impact on the theories and technical research of refinement, and the broadening of the application field of master alloys. This paper first summarizes the grain refinement mechanisms and analyzes the effects of rare earth elements and transition elements on the grain refinement of aluminum and aluminum alloys, and summarizes the elements suitable for the preparation of Al-M master alloys and their refinement mechanism.

Experiments were carried out onboard the International Space Station using the electromagnetic levitation (EML) facility on dendritic growth in Al-35 at%Ni under primary solidification of the NiAl(B2)-phase. The “velocity versus undercooling” relationship shows an anomalous behavior. At low undercoolings, Δ T < 250 K, the velocity unexpectedly decreases with increasing undercooling. For higher undercoolings, Δ T > 250 K, the crystal velocity increases with increasing undercooling following a thermodynamically consistent trend. For such anomalous behavior, a special mechanism was identified through the different crystals having scales and dendritic morphology. The scaled front consists of numerous nuclei ahead of the crystal–liquid interface that occurs in the undercooling range featuring the negative slope for the crystal growth velocity at Δ T < 250 K. This unusual behavior is confirmed experimentally and explained theoretically using analytical solutions for the crystal growth front with the polydisperse ensemble of crystals nucleating ahead of it.