Solidification Pressure Research Articles

Microstructure and strengthening mechanism of Mg—5.88Zn—0.53Cu—0.16Zr alloy solidified under high pressure

Mg—5.88Zn—0.53Cu—0.16Zr (wt.%) alloy was solidified at 2—6 GPa using high-pressure solidification technology. The microstructure, strengthening mechanism and compressive properties at room temperature were studied using SEM and XRD. The results showed that the microstructure was refined and the secondary dendrite spacing changed from 35 μm at atmospheric pressure to 10 μm at 6 GPa gradually. Also, Mg(Zn,Cu)2 and MgZnCu eutectic phases were distributed in the shape of network, while under high pressures the second phases (Mg(Zn,Cu)2 and Mg7Zn3) were mainly granular or strip-like. The solid solubility of Zn and Cu in the matrix built up over increasing solidification pressure and reached 4.12% and 0.32% respectively at 6 GPa. The hardness value was HV 90 and the maximum compression resistance was 430 MPa. Therefore, the grain refinement strengthening, the second phase strengthening and the solid solution strengthening are the principal strengthening mechanisms.

PRODUCTION OF AA7075/B4C COMPOSITE MATERIALS BY SEMI-SOLID STIRRING METHOD

AA7075 aluminum alloy was reinforced with B 4 C particles to produce aluminum composite materials. In the production of AA7075/B 4 C composite materials, semi-solid mixing methods were applied for homogen reinforcement dispersion then low pressure solidification. For the determination of the mechanical properties of the obtained samples; three point bending, compression and hardness tests were performed. In addition, microstructure, reinforcement matrix interface and chemical structure of the composite material produced by SEM, EDS, XRD analysis were examined. As a result, it was observed that; using the semi-solid mixing method the reinforcing powders could be distributed homogeneously into the matrix, both chemical and mechanical bonding could be occurs between the matrix and the reinforcing material and this mixing technique could be easily used in the production of particle reinforced metal composites.

Room temperature compressive properties and strengthening mechanism of Mg96.17Zn3.15Y0.50Zr0.18 alloy solidified under high pressure

The microstructures of Mg96.17Zn3.15Y0.50Zr0.18 alloys solidified under 2–6 GPa high pressure were investigated by employing SEM (EDS) and TEM. The strengthening mechanism of experimental alloy solidified under high pressure is also discussed by analyzing the compressive properties and compression fracture morphology. The results show that the microstructure of experimental alloy becomes significantly fine-grained with increasing GPa level high pressure during solidification process, and the secondary dendrite arm spacing reduces from 40 μm at atmospheric pressure to 10 μm at 6 GPa pressure. The morphology of the second phases changes from the net structure by the lamellar-type eutectic structure at atmospheric pressure to discontinuous thin rods or particles at 6 GPa pressure. Besides, the solid solubility of Zn in the Mg matrix is improved with the increase of the solidification pressure. Compared with atmospheric-pressure solidification, high-pressure solidification can improve the strength of the experimental alloy. The compressive strength is improved from 263 to 437 MPa at 6 GPa. The fracture mechanism of the experimental alloy changes from cleavage fracture at atmospheric pressure to quasi-cleavage fracture at high pressure. The main mechanism of the strength improvement of the experimental alloy includes the grain refinement strengthening caused by the refinement of the solidification microstructure, the second phase strengthening caused by the improvement of the morphology and distribution of the second phases, and solid solution strengthening caused by the increase of the solid solubility of Zn in the Mg matrix.

Raman spectroscopy of solid-phase n-dodecane and methyl oleate under high pressure.

Room-temperature Raman spectra of n-dodecane and methyl oleate were acquired at pressures up to 4 GPa. Both have monoalkyl chains with characteristic Raman rotamer profiles (trans and gauche conformers) along the skeletal CC bonds. The trans conformer was dominant in the high-pressure solid phase of n-dodecane. In solid methyl oleate, most of the gauche conformers transformed to the trans conformers. The all-trans dominated in the high-pressure solid phase and a triclinic subcell structure was indicated on the basis of previous vibrational spectra of n-alkanes and lipids. The solidification pressure of methyl oleate was determined against temperature up to 413 K.

Microstructure evolution of A380 aluminum alloy during rheological process under applied pressure

In squeeze casting process, the essence of mold-filling and feeding is rheological solidification of the alloy melt under pressure. Microstructure evolution is inevitable in this process, which affects the mold-filling and feeding in turn. In this work, the Archimedes spiral sample prepared by indirect squeeze casting was applied to investigate the microstructure evolution during the rheological process under pressure. The results showed that the primary α-Al phase was transformed from fine rosette-like or granular structure to coarse platelet-like structure with the increase of spiral length. However, the primary α-Al grain size of the starting point had a slight growing trend compared with that at the position of 140 mm away from the starting point. The volume fraction of the primary α-Al phase increased from 45.57% to 70.35% along the spiral length direction, demonstrating that the experimental pressure improved the rheological ability of the alloy melt to some extent. Furthermore, the eutectic Si phase was varied from a fine granular or wormlike structure to a coarse platelet-like or needle-like structure, and the dispersion of eutectic Si particles was also varied along the spiral length direction. This microstructure evolution was mainly owing to the comprehensive action of rheological solidification and pressurized solidification. More specifically, the microstructure evolution strongly depended on the pressure and rheological velocity during the rheological process, however, the effect of rheological distance was relatively small.

Effects of Solidification Pressure and Heat Treatment on the Microstructure and Micro-Hardness of AlSi9CuMg Alloy.

The effect of high pressure (135 MPa) and the following heat treatment on the microstructure and micro-hardness of the squeezing cast AlSi9CuMg alloy is investigated, using optical microscopy (OM), Vickers tester, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicate that the application of high pressure can increase under-cooling and the cooling rate during solidification and cause the refinement of the microstructure. The enhanced melt flow resulting from high pressure can also break the dendrite to form the spherical and elliptical primary α (Al) grains during the early stage of solidification. The winter-sweet flower-shaped primary α (Al) phases can also be formed through plastic deformation caused by the flow of the partially solidified melt. The ageing treatment results showed that a maximum (peak) micro-hardness value was obtained for each of the three ageing temperatures at different ageing times, and the highest peak value was achieved at 175 °C for 480 min. The micro-hardness change of the sample under different ageing processes was attributed to the variation of type, density, and size of the precipitates.

Structure of the Al90Y10 Alloy Formed upon Pressure Solidification

The effect of temperature and the melt cooling rate on the structure of an Al90Y10 alloy after high-pressure solidification is comparatively studied by X-ray diffraction analysis, optical microscopy, and electron microscopy. Only the crystalline α-Al and Al3Y phases form in the Al90Y10 alloy under all considered solidification conditions. The effect of the temperature, the cooling rate, and the pressure on the morphology, the size, and the microhardness of the structural alloy constituents, such as primary yttrium aluminide and eutectic crystals, is found.

Effect of synergistic action of ultrasonic vibration and solidification pressure on tensile properties of vacuum counter-pressure casting aluminum alloy

The effect of synergistic action of ultrasonic vibration and solidification pressure on tensile properties of vacuum counter-pressure casting ZL114A alloys was studied systemically through testing and analyzing the tensile strength and elongation subjected to different ultrasonic powers and solidification pressures. The results indicate that the synergistic action of ultrasonic vibration and solidification pressure can result in the refinement of grains and improvement of tensile properties. Both the highest tensile strength and elongation of aluminum alloy were obtained under synergistic action of 600 W ultrasonic power and 350 kPa solidification pressure. Moreover, the tensile fracture morphology shows obvious ductile fracture characteristics. When the solidification pressure is lower than 300 kPa, the effect of ultrasonic power on tensile strength and elongation is more obvious, but when the solidification pressure is higher than 300 kPa, the effect of solidification pressure on tensile strength and elongation is greater. Meanwhile, the size and morphology of the eutectic silicon were improved significantly by the ultrasonic vibration and pressurized solidification. The strip and massive eutectic silicon phase are completely converted into small short rod-like and evenly distributed Si phases at the grain boundary of primary α-Al.

The Influence Of Sand Casting Mold Solidfication Pressure Variations To The Quality Of Al-Si Alloy Casting Product

The purpose of this study is to find The influence of the sand cast solidification pressure variations to the quality of an alloy Al-Si casting product. An experimental method was used in the study and the analysis of the data used descriptive analysis to explain the charts. The stages of researched process is preparation material and equipment; making the design and manufacture of a pattern; manufacture of the sand mold by 35, 40, 45, 50, and 55 kg/cm 2 pressure variation; casting process; observation of defect; measurement of the level roughness; microstructure examination; assay composition; and last test is hardness micro vickers test. The research results show that variations pressure 35 kg/cm 2 does not occur defect the needle at al. A defect of the needle that occur most frequently upon variations of the pressure of the 55 kg/cm 2 is as much as 0.62 % . Air cavities formed to variation pressure solidification 35 kg/cm 2 of 0.77 % to the least, while in variation 55 kg/cm 2 happened the number of defect air cavities the most namely 3.96 % . The mold fall defect largest namely 1.95 % happened to variation pressure 35 kg/cm 2 . Defect of sand inclusion the least of 0.06 % happened to variation pressure 55 kg/cm 2 . Defect of fins formed due to variation pressure solidification sand mold experienced the number of been fluctuating, recorded high in early then decline and to high back in highest variation. The pressure variation 35 kg/cm 2 it has value roughness flattened 3.17 and products castings the most rough happened to sand mold solidification variation pressure 55 kg/cm 2 , with on average of 5.44. the degree of hardness highest of 141.8 VHN happened to variation pressure 35 kg/cm 2 and lowest of 124.8 VHN happened to variation 55 kg/cm 2 . Concluded that the solidification of pressure variations sand mold 45 kg / cm 2 produce castings products with the most optimal average in terms of the measurement of the defective; variation pressure solidification sand mold of sand casting 35 kg / cm 2 produce a smooth surface, and the higher pressure make surface castings becomes rougher; solidification of pressure variations and coarse sand mold 35 kg / cm 2 produce micro structure with smooth grains and becomes more violent along with increasing pressure; pressure variation 35 kg / cm 2 produce a hardest surface, the higher of the pressure variation it becoming violence number progressively lower. Keywords : Pressure variations, sand casting, quality

Development of Ultra High Performance Concrete and Reactive Powder Concrete with Nanosilica

The article is dedicated to the design and production of Ultra High Performance Concrete (UHPC) and Reactive Powder Concrete (RPC) using silica fume and nanosilica. Nanosilica and fine steel fibres were used for the production of RPC. Compressive strengths of UHPC and RPC above 150 MPa have been achieved. It has been demonstrated that UHPC and RPC can be produced using standard concrete mixing system without the use of activating mixing and without a special treatment regime during maturing of the concrete. Aging of the concrete took place in a normal environment, without elevated pressure or temperature. The aging process at 20 °C allows the use of UHPC and RPC for the ready-mixed concrete when working on high volume construction projects. Even without thermal treatment, without the application of solidification pressure and without autoclaving, RPC reached a compressive strength of more than 180 MPa and a flexural tensile strength after 60 days greater than 22 MPa. The high tensile bending strength may be considered as the main advantage of RPC, as the RPC parameters allow, for instance, the use for pre-stressed structural elements where a high initial strength is also required.

Effect of Solidification Pressure on Thermodynamic and Kinetic Parameters of 19Cr14Mn4Mo0.9N High Nitrogen Steel

The influence of solidification pressure on the thermodynamic and kinetic parameters of 19Cr14Mn4Mo0.9N high nitrogen steel is clarified by Thermo‐Calc/DICTRA software, including phase diagram, solidification mode, liquidus/solidus temperature, nitrogen solubility, partition coefficient, diffusion coefficient, driving force for nucleation, and diffusion coefficient. On this basis, the effect of pressure on critical nucleation radius and nucleation rate is also revealed. In the calculated vertical sections of 19Cr14Mn4Mo‐xN alloy phase diagram, δ single‐phase region decreases, both γ single‐phase region and three‐phase region L + δ + γ increase with increasing pressure. Additionally, the reaction mode of solidification transition gradually turns from peritectic to eutectic reaction, and the solidification mode changes from FA to A mode. Increasing the partial pressure of nitrogen can suppress the formation of ferrite trap and increase nitrogen solubility. Meanwhile, the partition coefficients of C, N, Cr, and Si increase, that of Mn and Mo decreases, resulting in decrease of C, N, and Cr microsegregation and improvement of Si, Mn, and Mo microsegregation. Pressurization has a small impact on diffusion coefficients, but it obviously promote the driving force for produced phase (δ and γ) nucleation, this lead to the decrease of critical nucleation radius, improvement of nucleation rate, and grain refinement of 19Cr14Mn4Mo0.9N high nitrogen steel.

Novel technologies for the lost foam casting process

Lost foam casting (LFC) is a green precision casting process categorized as a near net forming technology. Yet, despite its popularity, it still suffers from some technological problems, such as poor filling ability of the castings, coarse and non-dense microstructure, low mechanical properties for the Al and Mg LFC processes, and defective carburization for the low carbon steel LFC process. These drawbacks restrict the development and widespread application of the LFC process. To solve these problems, the present study developed several novel LFC technologies, namely, LFC technologies under vacuum and low pressure, vibration solidification, and pressure solidification conditions; expendable shell casting technology; and preparation technology of bimetallic castings based on the LFC process. The results showed that the LFC under vacuum and low pressure evidently improved the filling ability and solved the oxidization problem of the alloys, which is suitable for producing complex and thinwall castings. The vibration and pressure solidifications increased the compactness of the castings and refined the microstructure, significantly improving the mechanical properties of the castings. The expendable shell casting technology could solve the pore, carburization, and inclusion defects of the traditional LFC method, obtaining castings with acceptable surface quality. Moreover, the Al/Mg and Al/Al bimetallic castings with acceptable metallurgical bonding were successfully fabricated using the LFC process. These proposed novel LFC technologies can solve the current technological issues and promote the technological progress of the LFC process.

The formation of bulk β-Al3Ni phase in eutectic Al-5.69wt%Ni alloy solidified under high pressure

The microstructure and formation thermodynamic of bulk β-Al3Ni phase in eutectic Al-5.69wt%Ni alloy synthesized under different pressures were systematically investigated. The results demonstrate that α, bulk β-Al3Ni, and eutectic phase exist simultaneously after solidified under 1 GPa and 2 GPa. A mathematical model was proposed to describe the interfacial solidification velocity of dilute solution alloy under high pressure, with combination of the growth model of BCT and TMK, it reveals that the β-Al3Ni phase takes precedence over the eutectic phase nucleation when the solidification pressure is greater than 0.66 GPa.

Effect of Solidification Pressure on Interfacial Heat Transfer and Solidification Structure of 19Cr14Mn0.9N High Nitrogen Steel

Effect of Solidification Pressure on Interfacial Heat Transfer and Solidification Structure of 19Cr14Mn0.9N High Nitrogen Steel

Electron back-scattering diffraction preliminary analysis of heterogeneous nuclei in magnesium alloy during solidification process under GPa high pressure

The effective heterogeneous nuclei in Mg-7.92 Zn-1.70 Y alloy during solidification process under high pressure was investigated by EBSD. It is found that the orientation relationship between Mg matrix and MgY phase, [111]MgY//[1210]α-Mg and (101)MgY//(0001)α-Mg, exists between Mg matrix and MgY phase. The MgY phase is the potential heterogeneous nuclei substrate for α-Mg solidified under high pressure. It is calculated by Bramfitt mode that the mismatch between Mg matrix and MgY phase is greater than 12% under atmospheric pressure. When solidified under high pressure of 4 GPa, the solidification pressure can increase the number of the α-Mg nucleus by reducing the size of the nucleus, decreasing interfacial energy of MgY/α-Mg, and changing the wettability between MgY phase and α-Mg from non-wetting under atmospheric pressure to wetting under high pressure. The MgY phase becomes a powerful heterogeneous nuclei for α-Mg crystal. Increasing the number of valid heterogeneous nuclei substrate increases nucleus number and refines the grain of the alloy.

Dynamic recrystallization kinetic of fine grained Mg-Zn-Y-Zr alloy solidified under high pressure

Fine grained Mg96.17Zn3.15Y0.79Zr0.18 alloy with an average grain size of 20 μm was prepared by high pressure solidification. The dynamic recrystallization (DRX) behavior of the fine grained Mg alloy solidified under the pressure of 4 GPa was studied via isothermal compression experiments. The tests were performed under the strain rate of 0.001–1.0 s−1 and at a deformation temperature of 523–623 K on a Gleeble-3500D thermal-mechanical simulation machine. The DRX kinetic of the fine grained Mg alloy solidified under high pressure was established, and the microstructures of the alloy under different hot compression conditions were analyzed by electron back-scattering diffraction (EBSD). According to the experimental results, the DRX kinetic model of the fine grain Mg alloy solidified under high pressure was XDRX=1-exp[-0.75445(ɛ-ɛcɛ*)1.066208]. The Avrami exponents of n and k were 1.066208 and 0.75445 respectively, higher than those in the conventional casting alloy. The DRX volume fraction of the fine grain Mg alloy solidified under the pressure had a tendency to increase obviously with the strain rate decreasing and the deformation temperature increasing, which is different from the one in the conventional casting alloy. When compressed at 523 K, the DRX volume fraction of the fine grained Mg alloy solidified under high pressure was 85% under the strain rate of 1.0 s−1 and could be up to 95% under the strain rate of 0.001 s−1. The DRX volume fraction of the conventional casting alloy was only 67% although under the condition of 623–0.001 s−1. It was shown that the fine grained Mg alloy solidified under high pressure had a strong DRX capacity.

Effect of high pressure on the melting and solidifying behavior of a railway frog steel

Microstructural evolutions of the railway frog steel solidified under different pressure were studied using OM, FEGSEM, and TEM. The influences of pressure on the solidification, grain sizes, and morphology of carbides of the steel were analyzed. It is found that the melting point of the steel increases with the pressure and the solidified microstructure under high pressure does not vary significantly with the melting temperature. The experimental results show that the solidified microstructure consisting of complete equiaxed dendrites is remarkably refined through the increase of pressure, with the mean dendrite arm spacing of about 24, 18, and 8 μm under 3, 6, and 10 GPa, respectively. It is also revealed by TEM observation that the precipitates change from needle-like and rhombic carbide (M3C) forms during normal (atmospheric) pressure solidification into nodulized hexagonal precipitate M7C3 at 3 GPa, and M23C6 at 6 GPa and 10 GPa, which is associated with the undercooling and distribution of the trace elements. The diameter of the precipitates is between 80 nm and 200 nm.

Effects of Nitrogen Segregation and Solubility on the Formation of Nitrogen Gas Pores in 21.5Cr-1.5Ni Duplex Stainless Steel

The nitrogen gas pore-formation mechanism was discussed with regard to the solidification of 21.5Cr-1.5Ni duplex stainless steels (DSSs) by considering nitrogen segregation and solubility. The segregation behavior of nitrogen was investigated with phase transformation using experimental detection methods and Thermo-Calc software calculations. The process associated with the formation of gas pores was illustrated clearly. The factors that influenced the formation of gas pores, including shrinkage, nitrogen content, solidification pressure, and alloying elements (Mn and Cr), were discussed in detail. The formation of nitrogen-rich phases [austenite phase (FCC), AlN, and hexagonal close packed] is beneficial to eliminate nitrogen segregation and suppressing gas pore formation. The nitrogen-depleted phase (ferrite phase (BCC)) exhibits an opposite effect. Regular gas pores are initially formed in locations consisting of the austenite phase. As the gas pores lengthen, ferrite and austenite phases alternately form around the gas pores. Solidification shrinkage can promote the formation of irregular gas pores at the centerline of the ingots. Increasing the nitrogen content is favorable to the formation of gas pores. Increasing solidification pressure is effective with regard to suppressing the formation of gas pore defects in DSSs. Increasing the Mn content can reduce the likelihood of gas pore formation; this can be attributed to the increased nitrogen solubility in the residual liquid surrounding the dendrites and the formation tendency of the nitrogen-rich phase. Increasing the Cr content exhibits a dual effect on gas pore formation, which is caused by the increased nitrogen solubility and segregation in the residual liquid.

A phase field model coupled with pressure-effect-embedded thermodynamic modeling for describing microstructure and microsegregation in pressurized solidification of a ternary magnesium alloy

This paper presents a phase field model for describing microstructure and microsegregation in pressurized solidification of a ternary magnesium alloy, which captured essential physics associated with pressurized solidification of multi-component system, including pressure-effect-embedded thermodynamic modeling (PEE thermodynamic modeling) and interactive diffusion. This model was applied to squeeze casting of a Mg-Al-Sn alloy and revealed that the applied pressure increased solute trapping and solute accumulation in front of solid/liquid interface, which are two opposite factors contributing to microsegregation. Governed by the mechanism, the microsegregation of solute Al aggravates with applied pressure considerably, while that of Sn is rarely influenced by the pressure.

Effect of the Pressure on Microstructure of A380 Aluminum Alloy Prepared by Squeeze Casting

Effects of the solidification pressure on microstructure and mechanical properties of A380 alloy have been experimentally investigated. The obtained results show that the microstructures of the A380 aluminum alloy is fined, the porosity is decreased and the mechanical properties is improved remarkably with the increase of the solidification pressure. When the squeeze pressure increases from 0 MPa to 75MPa, the size of dendrite arm space decreases from 914 μm to 313 μm, reduced by 66%; the eutectic tissue volume fraction increases from 22.5% to 41.36%; the porosity decreases from 4.91% to 1.23%; the secondary dendrite spacing decreases from 39 μm to 18 μm; the size of needle-like β-Al5FeSi phase decreases significantly, and a few Chinese script α-Fe phases was observed in the grain boundary.