Sequential Solidification Research Articles

Section dimension induced microstructure and mechanical properties variations of sequential solidified sand–cast Mg–10Gd–0.2La–0.1Zn–0.4Zr (wt%) alloy

Casting dimension significantly influences the quality and performance of finished products when employing a sequential solidification process. Tapered cylinder Mg–10Gd–0.2La–0.1Zn–0.4Zr (wt%) castings with variable section dimensions were fabricated by sand–cast process, and the role of section dimension on the solidification behavior, microstructures and mechanical properties under different thermal conditions were systematically investigated. Increasing section dimension from Φ23 mm to Φ32 mm, the average cooling rate during solidification decreases from 1.70 °C/s to 0.86 °C/s, and the actual chemical composition of Gd element descends from 10.39 ± 0.11 wt% to 10.05 ± 0.06 wt%. Meanwhile, the primary α–Mg grains are coarsened in size from 29 ± 2 μm to 39 ± 3 μm, and the area ratio of the secondary phase degrades from 1.87 ± 0.19 % to 1.14 ± 0.31 %. With a solution treatment of 500 °C × 8 h, the area ratio of the residual secondary phase rises from 0.55 ± 0.06 % to 0.75 ± 0.12 %, accompanied by the decrease of Gd solubility with a grand value of 0.33 wt%. The decline of Gd solubility is unfavorable for the precipitation of strengthening phases during the ageing treatment and leads to a reduction of ∼13.5% in the area number density of the β′ precipitates. The strength and ductility at ambient temperature simultaneously worsen with increasing section dimension, in which the yield strength, ultimate tensile strength and elongation respectively descend from 230 ± 7 MPa, 364 ± 7 MPa and 8.5 ± 1.1 % to 219 ± 6 MPa, 336 ± 5 MPa and 5.5 ± 0.9 % in the peak–aged condition. The strength debasement is due to the grain coarsening and lower number density of the β’ precipitates, while the reduced ductility is attributed to the coarser grains and higher content of the residual secondary phase with larger size. Casting dimensions should be meticulously designed when developing high–performance Mg alloys by sequential solidification processes.

Solvent-Exchange Triggered Solidification of Peptide/POM Coacervates for Enhancing the On-Site Underwater Adhesion

Peptide-based biomimetic underwater adhesives are emerging candidates for understanding the adhesion mechanism of natural proteins secreted by sessile organisms. However, there is a grand challenge in the functional recapitulation of the on-site interfacial spreading, adhesion and spontaneous solidification of native proteins in water using peptide adhesives without applied compressing pressure. Here, a solvent-exchange strategy was utilized to exert the underwater injection, on-site spreading, adhesion and sequential solidification of a series of peptide/polyoxometalate coacervates. The coacervates were first prepared in a mixed solution of water and organic solvents by rationally suppressing the non-covalent interactions. After switching to a water environment, the solvent exchange between bulk water and the organic solvent embedded in the matrix of the peptide/polyoxometalate coacervates recovered the hydrophobic effect by increasing the dielectric constant, resulting in a phase transition from soft coacervates to hard solid with enhanced bulk cohesion and thus compelling underwater adhesive performance. The key to this approach is the introduction of suitable organic solvents, which facilitate the control of the intermolecular interactions and the cross-linking density of the peptide/polyoxometalate adhesives in the course of solidification under the water line. The solvent-exchange method displays fascinating universality and compatibility with different peptide segments.

A multimodal data-driven design of low pressure die casting gating system for aluminum alloy cabin

The design of gating systems for large and complex thin-wall castings requires the application of empirical equations and a substantial number of iterative experiments. In this study, a novel machine learning-based design strategy is proposed for the gating system of large and complex thin-walled castings. The gating system of castings was estimated using a multi-input multi-output neural network model, which incorporated visual, textual, and numerical multimodal features. The R2 value of the model accuracy reached 0.981, and the predicted parameters for the gating system were a slot runner width of 27 mm, a slot runner length of 48 mm, a riser runner diameter of 60 mm, and the number of riser runners of 8. The EasyCast and Procast simulation software were utilized for comparison and verification, resulting in a smooth filling and the achievement of sequential solidification. Finally, the mechanism of casting defects is discussed using the solidification phase-field model of EasyPhase system, elucidating how the alloy system can serve as a distinguishing feature in machine learning models that impact gating system parameters. This strategy is anticipated to enhance the efficiency of low pressure die casting process design, thereby serving as a valuable reference for intelligent process design in low pressure die casting.

Process optimization of A356 aluminum alloy wheel hub fabricated by low-pressure die casting with simulation and experimental coupling methods

The aluminum alloy wheel hub is mainly produced by low-pressure die casting process (LPDC), in which casting quality is closely related to the process parameters. In this paper, the LPDC process of the A356 alloy wheel hub was numerically simulated by ProCAST software, and the forming quality of the wheel hub under different cooling processes has been studied. The result indicated that the liquid aluminum exhibited different solidification characteristics under three cooling processes of 300 L/h for 150 s, 400 L/h for 140 s and 500 L/h for 130 s. A sequential solidification state was obtained under the condition of 400 L/h for 140 s. By comparing the tensile properties of the rim under different cooling processes, it was found that the wheel hub casted under 400 L/h for 140 s had higher tensile strength and elongation, which were 178.9 MPa and 6.6%, respectively. The reduction of casting defects, microstructure refinement, and uniform distribution of eutectic Si particles in the wheel hub are the main reasons for the improvement of mechanical properties.

Sequential Solidification of Metal Powder by a Scanning Microwave Applicator.

This study examines the fundamental feasibility of sequential metal-powder solidification by localized microwave-heating (LMH) provided by a scanning, all-solid-state microwave applicator. This continuous process is considered for the additive manufacturing (AM) and 3D printing (3DP) applications of metal parts. In previous studies, we employed LMH for the incremental solidification of small batches of metal powder in a stepwise vertical manner. Here, we study a continuous lateral LMH process, layer by layer, in a fashion similar to laser scanning in powder beds, as performed in common laser-based AM systems. LMH solidification at scanning rates of ~1 mm3/s is obtained in bronze powder using ~0.25-kW microwave power. The effect is studied here by LMH scanning in one lateral dimension (~20-mm long) in layers, each of ~1-4 mm thickness and ~2-4 mm width (mechanically confined). Imperfect solid bars of ~20×4×5 mm3 are obtained with rough surfaces. Their joining in an L shape is also demonstrated. The experimental solidified products are tested, and their hardness and density properties are found to be comparable to laser-based AM products. The capabilities and limitations of the LMH scanning concept for metal-powder solidification are evaluated. The potential feasibility of a solid-state LMH-AM technology is discussed.

Optimizing Ni-rich intermetallic and mechanical properties at room and elevated temperatures for Al-Cu-Ni alloys by coupling travelling magnetic fields with sequential solidification

Nickel can enhance the elevated temperature property of Al alloys, but blocky and aggregated Ni-rich intermetallic induced by high Ni content can seriously reduce the properties at room and elevated temperatures. Accordingly, finding ways to optimize Ni-rich intermetallic and performance at room and elevated temperatures is of great significance. In this regard, we couple travelling magnetic fields (TMF) with sequential solidification to alter the content, morphology, distribution and growth of Ni-rich intermetallic in Al-Cu-based alloys with high Ni content, further to increase the related performance. Moreover, simulations are combined with experiments to comprehensively reveal the mechanisms on these optimizations during each stage of solidification process. Current findings indicate that Ni-rich intermetallic and matrix phase α-Al are effectively refined, modified and diffusely distributed, and growing in random directions by TMF process. Hence, the performance at both room and elevated temperatures are greatly improve. Specifically, Down-TMF increases the UTS, YS, elongation and hardness at 298 K from 147.8 MPa, 90.8 MPa, 6.0 % and 75.6 kg·mm−2 without TMF to 186.7 MPa, 102.7 MPa, 10.4 % and 85.2 kg·mm−2. While, Up-TMF raises them to 179.2 MPa, 95.1 MPa, 8.5 % and 83.2 kg·mm−2. Additionally, Dwon-TMF improves the UTS, YS and elongation at 473 K from 99.0 MPa, 77.6 MPa and 17.3 % without TMF to 153.7 MPa, 86.1 MPa and 18.2 %, and from 74.7 MPa, 65.6 MPa and 18.5 % at 573 K to 84.4 MPa, 75.8 MPa and 25.7 %. While, Up-TMF promotes their elevated performance to 162.9 MPa, 88.9 MPa and 17.6 % at 473 K, and to 87.2 MPa, 77.0 MPa and 22.5 % at 573 K, respectively. Noteworthily, Down-TMF generates more overall positive effects than Up-TMF.

High drug-loaded microspheres enabled by controlled in-droplet precipitation promote functional recovery after spinal cord injury

Drug delivery systems with high content of drug can minimize excipients administration, reduce side effects, improve therapeutic efficacy and/or promote patient compliance. However, engineering such systems is extremely challenging, as their loading capacity is inherently limited by the compatibility between drug molecules and carrier materials. To mitigate the drug-carrier compatibility limitation towards therapeutics encapsulation, we developed a sequential solidification strategy. In this strategy, the precisely controlled diffusion of solvents from droplets ensures the fast in-droplet precipitation of drug molecules prior to the solidification of polymer materials. After polymer solidification, a mass of drug nanoparticles is embedded in the polymer matrix, forming a nano-in-micro structured microsphere. All the obtained microspheres exhibit long-term storage stability, controlled release of drug molecules, and most importantly, high mass fraction of therapeutics (21.8–63.1 wt%). Benefiting from their high drug loading degree, the nano-in-micro structured acetalated dextran microspheres deliver a high dose of methylprednisolone (400 μg) within the limited administration volume (10 μL) by one single intrathecal injection. The amount of acetalated dextran used was 1/433 of that of low drug-loaded microspheres. Moreover, the controlled release of methylprednisolone from high drug-loaded microspheres contributes to improved therapeutic efficacy and reduced side effects than low drug-loaded microspheres and free drug in spinal cord injury therapy.

Mesoscopic numerical simulation and experimental investigation of laser powder bed fusion AlCu5MnCdVA alloys

AlCu5MnCdVA alloys had high specific strength, good machining and fatigue properties, outstanding electroplating and excellent corrosion resistance. However, due to wide crystallization temperature range, it is hard to realize sequential solidification for AlCu5MnCdVA alloy by traditional casting process. Laser Powder Bed Fusion (L-PBF) has become one of the most promising technology in Metal Additive Manufacturing (MAM). In this study, L-PBF was employed to fabricate AlCu5MnCdVA parts, and both mesoscopic numerical element model and experimental printing were applied to study the feasibility of L-PBF Additive Manufacturing AlCu5MnCdVA alloy. Relative densities, phase analysis and micromorphology were investigated systematically by SEM, EDS and XRD. The laser process parameters window for AlCu5MnCdVA were obtained: volumetric energy density 41–51 J mm−3, laser power 230–240W, laser scanning speed 1200–1325 mm s−1. And the relative density of parts fabricated by L-PBF reached 96.1%. Besides, AlCu5MnCdVA alloy fabricated by L-PBF was mainly consist of α-Al, little other phase such as Al2Cu or Al2Mn3 was detected.

Eliminating shrinkage defects and improving mechanical performance of large thin-walled ZL205A alloy castings by coupling travelling magnetic fields with sequential solidification

Abstract ZL205A alloys with large thin-walled shape were continuously processed by coupling travelling magnetic fields (TMF) with sequential solidification, to eliminate the shrinkage defects and optimize the mechanical performance. Through experiments and simulations, the parameter optimization of TMF and the influence on feeding behavior, microstructure and properties were systematically studied. The results indicate that the magnetic force maximizes at the excitation current of 20 A and frequency of 200 Hz under the experimental conditions of this study, and increases from center to side-walls, which is more convenient to process thin-walled castings. TMF can break secondary dendritic arm and dendrites overlaps, widen feeding channels, prolong the feeding time, optimize the feeding paths, eliminate shrinkage defects and improve properties. Specifically, for as-cast state, TMF with excitation current of 20 A increases ultimate tensile strength, elongation and micro-hardness from 186 MPa, 7.3% and 82.1 kg/mm2 to 221 MPa, 11.7% and 100.5 kg/mm2, decreases porosity from 1.71% to 0.22%, and alters brittle fracture to ductile fracture.

In situ synchrotron diffraction and modeling of non-equilibrium solidification of a MnFeCoNiCu alloy

The solidification mechanism and segregation behavior of laser-melted Mn35Fe5Co20Ni20Cu20 was firstly investigated via in situ synchrotron x-ray diffraction at millisecond temporal resolution. The transient composition evolution of the random solid solution during sequential solidification of dendritic and interdendritic regions complicates the analysis of synchrotron diffraction data via any single conventional tool, such as Rietveld refinement. Therefore, a novel approach combining a hard-sphere approximation model, thermodynamic simulation, thermal expansion measurement and microstructural characterization was developed to assist in a fundamental understanding of the evolution of local composition, lattice parameter, and dendrite volume fraction corresponding to the diffraction data. This methodology yields self-consistent results across different methods. Via this approach, four distinct stages were identified, including: (I) FCC dendrite solidification, (II) solidification of FCC interdendritic region, (III) solid-state interdiffusion and (IV) final cooling with marginal diffusion. It was found out that in Stage I, Cu and Mn were rejected into liquid as Mn35Fe5Co20Ni20Cu20 solidified dendritically. During Stage II, the lattice parameter disparity between dendrite and interdendritic region escalated as Cu and Mn continued segregating into the interdendritic region. After complete solidification, during Stage III, the lattice parameter disparity gradually decreases, demonstrating a degree of composition homogenization. The volume fraction of dendrites slightly grew from 58.3 to 65.5%, based on the evolving composition profile across a dendrite/interdendritic interface in diffusion calculations. Postmortem metallography further confirmed that dendrites have a volume fraction of 64.7% ± 5.3% in the final microstructure.

Reducing porosity and optimizing performance for Al-Cu-based alloys with large solidification intervals by coupling travelling magnetic fields with sequential solidification

Porosity is a major casting defect in alloys with large solidification intervals due to the disordered microstructure and broad mushy zones, which decreases badly the mechanical performance. Hence, finding ways to effectively reduce the porosity, further to optimize microstructure and mechanical performance is of great significance. In this regard, the Al-Cu-based alloys with large solidification intervals are continuously processed by coupling the travelling magnetic fields (TMF) with sequential solidification. Additionally, experiments combined with simulations are utilized to comprehensively analyze the mechanism of TMF on the reduction in porosity, including shrinkage porosity and gas porosity, from different perspectives. Current findings determine that downward TMF can effectually optimize together the porosity, microstructure and performance, by inducing the strong long-range directional melt flows, stabilizing the mushy zones, and optimizing the feeding channels and exhaust paths, as well as increasing the driving force of degassing process. Eventually, downward TMF can increase the ultimate tensile strength, yield strength, elongation and hardness from 175.2 MPa, 87.5 MPa, 13.3 % and 80.2 kg mm−2 without TMF to 218.6 MPa, 109.3 MPa, 15.6 % and 95.5 kg mm-2, while reduce the total porosity from 0.95 % to 0.18 %. However, Up-TMF exerts negative effects on the optimization of porosity, microstructure and performance due to the opposite strong directional magnetic force and melt flows. Overall, our study provides an effective way to optimize together the porosity, microstructure and mechanical performance, and reveals their relationship, as well as details the relevant mechanisms of TMF on the porosity reduction from different perspectives.

Optimizing the microstructures and mechanical properties of Al-Cu-based alloys with large solidification intervals by coupling travelling magnetic fields with sequential solidification

Alloys with large solidification intervals are prone to issues from the disordered growth and defect formation; accordingly, finding ways to effectively optimize the microstructure, further to improve the mechanical properties is of great importance. To this end, we couple travelling magnetic fields with sequential solidification to continuously regulate the mushy zones of Al-Cu-based alloys with large solidification intervals. Moreover, we combine experiments with simulations to comprehensively analyze the mechanisms on the optimization of microstructure and properties. Our results indicate that only downward travelling magnetic fields coupled with sequential solidification can obtain the refined and uniform microstructure, and promote the growth of matrix phase α-Al along the direction of temperature gradient. Additionally, the secondary dendrites and precipitates are reduced, while the solute partition coefficient and solute solid-solubility are raised. Ultimately, downward travelling magnetic fields can increase the ultimate tensile strength, yield strength, elongation and hardness from 196.2 MPa, 101.2 MPa, 14.5 % and 85.1 kg mm−2 without travelling magnetic fields to 224.1 MPa, 114.5 MPa, 17.1 % and 102.1 kg mm−2, and improve the ductility of alloys. However, upward travelling magnetic fields have the adverse effects on microstructural evolution, and lead to a reduction in the performance and ductility. Our findings demonstrate that long-range directional circular flows generated by travelling magnetic fields directionally alter the transformation and redistribution of solutes and temperature, which finally influences the solidification behavior and performance. Overall, our research present not only an innovative method to optimize the microstructures and mechanical properties for alloys with large solidification intervals, but also a detailed mechanism of travelling magnetic fields on this optimization during the sequential solidification.

Effects of Process Parameters on Shrinkage Porosity in 357 Semi-Solid Die Casting Parts

The shrinkage porosity that was caused by the insufficient feeding during solidification, was a common defect in the semi-solid die casting process. This defect decreased significantly the mechanical properties of the casting. In order to avoid the shrinkage porosity in casting, the die design, slug preparation and die casting process were carefully considered. In this study, a designed mold was used to make the sequential solidification of the slug. The process parameters, including intensification pressure, die temperature and biscuit thickness of the casting, were studied to show their influence on shrinkage porosity defects. The experimental results show that the high intensification pressure, high die temperature and long biscuit can be beneficial to obtain castings with no shrinkage porosity.

Numerical study of the effect of progressive solidification on residual stress in single-bead-on-plate additive manufacturing

The additive manufacturing of metals and ceramics generally uses a concentrated laser heat source to form a local melt pool that moves quickly during the process. The material is deposited by fast cooling and progressive solidification. In this study, the effects of temperature gradient and progressive solidification on residual stress were analyzed using numerical finite-element models for a single rapidly solidifying bead during the deposition process. Conceptual two- and three-dimensional finite element models are proposed, considering the solidification effect. Based on the numerical results, a reduced-order modeling strategy was proposed to efficiently reproduce the final residual stress state of single-bead deposition processes in additive manufacturing, i.e. sequential solidification.

Fabrication of functionally radial graded metallic foam

Radial graded structures in biological materials, e.g. bones, are lightweight and exhibit good mechanical properties. This paper developed a novel method to fabricate a functionally radial graded aluminum foam. In this method, a sequential solidification was applied from the periphery to the inner on the foaming aluminum melt to obtain a radial gradient. The graded foams were then served as fillers for thin-walled tubes. Quasi-static compressive tests were conducted on the foams and foam-filled tubes. The results indicated that the graded foam-filled tubes exhibited improved crushing resistance and specific energy absorption, compared to the uniform foam-filled tube with similar weight.

Effects of radiative local heating on metal solidification during selective laser melting for additive manufacturing

Selective laser melting (SLM) is a promising additive manufacturing technique arising from glassy metal characteristics of treated medium. When creating novel compositions of materials and intricate workpieces, reliable thermal designs should be implemented based on well-understood heat transfer characteristics on matierlas to be used. Herein, we investigate local and overall heat transfer characteristics of SLM processes and investigate the principal parameters related to the magnituge of a radiative heating power and its exposure time. We present how to exert their influence upon local melting and sequential solidification of copper powder bed. The local solid media reach a quasi-equilibrium state in even 1 ms with the incident powers of 50, 100, and 200 W. The anisotropic expansion of the molten pool is governed by a thermally-induced Marangoni flow. As the power is increased, the Marangoni factor increases linearly up to 853.7%. Consequential heat transfer characteristics tell us that unconditional input power should be avoided to prohibit the detrimental effect; the radiative heating power should be confined for thermalization of a target domain and for that preventing the evaporation of a material. These approaches from material science to heat transfer can be used to develop a platform for SLM processes guaranteeing its feasibility and applicability.

Control of MnS Inclusions in High- and Low-Sulfur Steel by Tellurium Treatment.

Manganese sulfide (MnS) inclusion in steel is related to the machinability of steel. Controlling the type and shape of MnS inclusion has been a problem for the steelmaking process for a long time. The effect of tellurium (Te) treatment on the control of MnS inclusion is studied with experiments and discussion of sequential solidification. The result shows that Te addition to the high- and low-sulfur steel dominantly changes the size and shape of MnS inclusions in steel. The aspect ratio of inclusions in cast steel changes with Te/S ranges from 0 to 1.9, which offers an effective way to control the MnS type and thus to improve the machinability and mechanical properties of steel. With an excessive Te addition, no further improvement could be observed by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS).

Selective laser melting of nano-TiB2 decorated AlSi10Mg alloy with high fracture strength and ductility

An in-situ nano-TiB2 decorated AlSi10Mg composite (NTD-Al) powder was fabricated by gas-atomisation for selective laser melting (SLM). Fully dense and crack-free NTD-Al samples were produced using SLM. In contrast to the NTD-Al powder without cell-like microstructure, the SLMed NTD-Al had a textureless microstructure, consisting of fine grains and cells, with well dispersed nano-TiB2 particles inside the grains and rod-like nano-Si precipitates inside the cells. Both nano-TiB2 particles and nano-Si precipitates exhibited a highly coherent interface with the Al matrix, indicative of a strong interfacial bonding. The formation of this microstructure was attributed to the sequential solidification of non-equilibrium and eutectic Al-Si upon rapid cooling during SLM. As a result, the SLMed NTD-Al showed a very high ultimate tensile strength ∼530 MPa, excellent ductility ∼15.5% and high microhardness ∼191 HV0.3, which were higher than most conventionally fabricated wrought and tempered Al alloys, previously SLMed Al-Si alloys and nano-grained 7075 Al. The underlying mechanisms for this strength and ductility enhancement were discussed and a correlation between this novel microstructure and the superior mechanical properties was established. This study provides new and deep insights into the fabrication of metal matrix nanocomposites by SLM from in-situ pre-decorated composite powder.

Numerical Simulation of Filling and Solidification in Sand Casting by Procast

At present, pulley produced in China has been able to meet the demand of domestic and international markets. But there are many problem of the pulley industry in our country, such as too many production enterprises and the low level of export products. And as components of drive system are light weight and raw material price of pulley casting are rising, manufacturing requirements of the pulley are also more and more high. Aiming at the casting defects of pulley that enterprise current product, pulley casting blank model of common material HT250 be made by three-dimension software, numerical simulation of filling and solidification process for pulley sand casting by the casting simulation software Procast, the size and location of the various casting defects were forecasted and analyzed, reflecting the pulley filling and solidification process of the actual situation, due to the thicker pulley rim and less heat dissipation, position of shrinkage is close to the middle of rim [, a method of eliminating defects is proposed to realize sequential solidification, and thus to minimize porosity shrinkage and improve casting performance and reduce casting time and reduce production costs.

Effects and Mechanism of Titanium on Cast Fluidity of ZG45

The effects of titanium modification, which was added along with the pouring liquid in ladles, on the shrinkage porosity and cavity of cast steel ZG45 smelted in intermediate frequency induction furnace were studied. The metal liquid fluidity was measured by casting spiral samples. 0.2 wt.% titanium modification achieved the highest fluidity for steel liquid. Proper content of titanium could effectively increase the volume of concentrated shrinkage cavity, and restrain the forming of shrinkage porosity. By scanning electron microscope (SEM) and energy disperse spectroscope (EDS) analysis, it was found that TiC, acting as heterogeneous nuclei, could refine the structure grains, diminish the strong dendrite, and increase the fluidity and feeding capacity of steel liquid. However, overdoes titanium modification easily caused mass oxide TiO2, which kept solid phases with high meting point in metal liquid to increase its viscosity and decrease the fluidity. Meanwhile, these solid state titanium compounds enlarged the composition supercooling, so the metal liquid changed from sequential solidification to simultaneous solidification, resulting in inadequate metal liquid feeding, less oncentrated shrinkage cavity and serious shrinkage porosity.