Influence of cooling rate on solidification behavior of sand-cast Mg-10Gd-3Y-0.4Zr alloy

The effect of the cooling rate ranging from 1.4 °C/s to 3.5 °C/s on the solidification behavior of the sand-cast Mg?10Gd?3Y?0.4Zr alloy was studied by computer aided cooling curve analysis (CA-CCA). With the increase in cooling rate, the nucleation temperature (Tα,N) increases from 634.8 °C to 636.3 °C, the minimum temperature (Tα,Min) decreases from 631.9 °C to 630.7 °C, the nucleation undercooling (ΔTN) increases from 2.9 °C to 5.6 °C, the beginning temperature of the eutectic reaction (Teut,N) increases, the time of the eutectic reaction shortens, solidus temperature decreases from 546.0 °C to 541.4 °C, and solidification temperature range (ΔTS) increases by 6.1 °C. The increased nucleation rate (N&) is supposed to be the main reason for the increased?TN. Increased value (Teut,N?Teut,G) and shortened time of the eutectic reaction cause the change in the volume fraction and morphology of the second phase.

Microstructure characteristics and solidification behavior of thixomolded Mg-9%Al-1%Zn alloy

Experimental investigation and theoretical analysis of the microstructure of thixomolded AZ91D were carried out to comprehensively understand the morphology transformation of solid particles and the solidification behavior. Typical microstructure of thixomolded AZ91D is composed of a-Mg and β-Mg17Al12, characterized with aun, aprim and eutectic. Four kinds of aun are classified according to the morphology and generation mechanism, such as spherical （al）, irregular （a2）, entrapping liquid alloy inside （a3） and entrapping pool inside （a4）. Under the effect of heating, shearing, collision, agglomeration or fragmentation, a2 and a4 can be the middle states ofal and a3. Similarly, a4 and a3 can also break into a2 and become al at the end. Controlled by undercooling, aprim nucleates and spherically grows within the remaining liquid alloy of thixomolded AZ91D until instability growth. The investigated microstructure was theoretically proved according to the analysis of Mg-Al binary phase diagram.

Microstructure characteristics and solidification behavior of wrought aluminum alloy 2024 rheo-diecast with self-inoculation method

One important problem in casting wrought aluminum alloys is the high tendency to the formation of hot tears in the solidification process.By using semi-solid metal(SSM) processing,the hot tearing tendency of alloys can be minimized during casting.In the present research,the semi-solid slurry of wrought aluminum alloy 2024 was firstly prepared with a novel self-inoculation method(SIM),and then the microstructure characteristics of the semi-solid slurry and the rheo-diecastings cast with the semi-solid slurry were investigated.The results indicate that finer and more uniform globular primary α-Al particles can be obtained when the semi-solid slurry are isothermally held for a short period within the semi-solid temperature range,and the primary α-Al particles without entrapped liquid are uniformly fine,globular grains in the rheo-diecastings.The holding temperature and time affect the solid fraction,particle size,and shape factor.After the semi-solid slurry is held at 625 ℃ for 3 min and 5 min,the optimal values for the average equivalent diameter are 70.80 μm and 74.15 μm,and for the shape factor are 1.32 and 1.42,respectively.The solidification process of the rheo-diecastings is composed of the following two distinct stages:primary solidification process and secondary solidification process.The secondary solidification process consists further of the following three stages:(1) direct growth of secondary primary(α 2) phase from the surface of the primary α-Al phase particles without re-nucleation,(2) independent nucleation and growth of α 3 phase from the residual liquid,and(3) eutectic reaction at the end.

Structure Evolution and Solidification Behavior of Austenitic Stainless Steel in Pulsed Magnetic Field

To understand the solidification behavior of austenitic stainless steel in pulsed magnetic field, the solidification process is investigated by means of the self-made high voltage pulse power source and the solidification tester. The results show that the solidification structure of austenitic stainless steel can be remarkably refined in pulsed magnetic field, yet the grains become coarse again when the magnetic intensity is exceedingly large, indicating that an optimal intensity range existed for structure refinement. The solidification temperature can be enhanced with an increase in the magnetic intensity. The solidification time is shortened obviously, but the shortening degree is reduced with the increase of the magnetic intensity.

Effect of Zr modification on solidification behavior and mechanical properties of Mg–Y–RE (WE54) alloy

Magnesium alloys containing rare earth elements (RE) have received considerable attention in recent years due to their high mechanical strength and good heat-resisting performance. Among them, Mg–5%Y–4%RE (WE54) magnesium alloy is a high strength sand casting magnesium alloy for use at temperatures up to 300 ℃, which is of great interest to engineers in the aerospace industry. In the present work, the solidification behavior of Zr-containing WE54 alloy and Zr-free alloy was investigated by computer-aided cooling curve analysis (CA-CCA) technique. And the solidification microstructure and mechanical properties of them were also investigated comparatively. It is found from the cooling curves and as-cast microstructure of WE54 alloy that the nucleation temperature of α-Mg in WE54 alloy increases after Zr addition, and the as-cast microstructure of the alloy is significantly refined by Zr. While the phase constitution of WE54 alloy is not changed after Zr addition. These phenomena indicate that Zr acts as heterogeneous nuclei during the solidification of WE54 alloy. Due to refined microstructure, the mechanical properties of Zr-containing WE54 alloy is much higher than Zr-free WE54 alloy.

Solidification behavior of 6061 wrought aluminum alloy during rheo-diecasting process with self-inoculation method

The semisolid slurry of the 6061 wrought aluminum alloy was prepared by the self-inoculation method（SIM）. The effects of the isothermal holding parameters on microstructures of rheo-diecastings were investigated, and the solidification behavior of 6061 wrought aluminum alloy during the rheo-diecasting process was analyzed using OM, SEM, EDS and EBSD. The results indicate that the isothermal holding process during slurry preparation has great effect on primary α（Al） particles（α1）, but has little effect on the microstructure of secondary solidification in the process of thin-walled rheo-diecasting. Nucleation is expected to take place in the entire remaining liquid when the remaining liquid fills the die cavity, and the secondary solidification particles（α2） are formed after the process of stable growth, unstable growth and merging. The solute concentration of remaining liquid is higher than that of the original alloy due to the existence of α1 particles, hence the contents of Mg and Si in α2 particles are higher than those in α1 particles.

Thermodynamic descriptions of quaternary Mg-Al-Zn-Bi system supported by experiments and their application in descriptions of solidification behavior in Bi-additional AZ casting alloys

16 Mg-Al-Zn-Bi quaternary alloys were utilized to measure the phase equilibria and transformation temperatures in the Mg-rich Mg-Al-Zn-Bi quaternary system by means of the X-ray diffraction,electron probe micro-analysis and differential scanning calorimetry techniques.The isothermal section at 400℃and three vertical sections along Mg-8 wt%Al-0.75 wt%Zn-vBi,Mg-3.4 wt%Al-0.5 wt%Zn-ABi and Mg-6.9 wt%Al-2.3 wt%Zn-xBi in the Mg-Al-Zn-Bi quaternary system were constructed.Based on the literature data,the ternary Mg-Al-Bi and Mg-Bi-Zn systems were re-assessed using the CALculaiton of PHAse Diagram(CALPHAD)approach.The calculated phase equilibria agree well with the measured data.By directly extrapolating the constituent sub-ternary systems,the thermodynamic database for the Mg-Al-Zn-Bi quaternary system was developed.The remarkable consistency between the predicted phase equilibria and the presently measured data in Mg-Al-Zn-Bi quaternary system further demonstrated the accuracy and reliability of the established thermodynamic database.After that,by using the newly developed thermodynamic database,the growth restrict factors and the solidification curves in Bi-containing AZ series magnesium alloys were calculated and analyzed.It was confirmed that the grain size of AZ alloys can be refined with the addition of Bi,and the comp on ent Al had larger grain refinement effect than Bi.Besides,the amount of Bi had also no ticeable effect on the solidification sequence of the AZ alloys.

Metallurgical modeling of microcrack repairment during welding nonferrous materials: non-equilibrium solidification behavior of weld pool (Ⅰ)

Metallurgical modeling of synergistic microcrack self-repairmen during welding single crystal and polycrystalline superalloys of high-temperature aerospace materials has been properly established. The idea of improvement of nickel-based superalloys weldability through non-equilibrium solidification behavior of backfill to self-repair arterial crack network is usefully proposed. Crystallographic control strategy of crack self-repairmen of fusion zone interdendritic solidification cracking and heat-affected zone （HAZ） intergranular liquation cracking is technically achievable, indicating that optimal niobium alloying beneficially refines weld microstructure, stabilizes the primary solidification path, increases the solidification temperature and concomitantly decreases the weld pool geometry. High-carbon grain boundary is more thermal stable and less contributes to incipient intergranular liquid film than that of low-carbon grain boundary. The theoretical predictions of cracking susceptibility are indirectly verified in a rather satisfactory manner. Additionally, the metallurgical modeling enhances predicative capabilities and thereby is readily applicable for other alloy systems.

Effect of Pressure on the Solidification Behavior and Mechanical Properties of SiCp/Al-Mg Composites

SiCp/A1-Mg metal matrix composites were manufactured by semi-solid stirring technique. The composites were remelted and then solidified under different pressures to study the solidification behavior of composites by differential thermal analysis, scanning electron microscopy, and transmission electron microscopy. The experimental results show that SiCp reinforcements can not act as heterogeneous nucleation sites for c^（A1）, and an interfacial layer composed of MgA1204 spinel and Si-rich phase existed at A1/SiCp interface. The undercooling of the matrix alloy was improved by the pressure applied, resulting in the grain of matrix alloy refining. The X-ray diffraction pattern of composites testified that the matrix alloy exhibited a certain preferred orientation during solidification. In addition, with increasing the pressure for solidification, the pored defects in the composites decreased, while the relative density, hardness and compressive strength increased. Therefore, the microstructure and mechanical properties of the composites were improved by pressure placed during the solidification of SiCp/A1-Mg composites.

THE EFFECT OF RARE EARTH ELEMENTS ON THE SOLIDIFICATION BEHAVIOR OF Al-Mg ALLOYS

The effect of rare earth element on the solidification behavior of Al-Mg alloy was investigated in a directional solidification apparatus.It was found that during the solidification process.the rare earth element segregated in the liquid at sold-liquid interface,changed the solidification morphology and reduced the secondary arm spacing markedly.

Solidification behavior of Pt-containing 718Plus superalloy

Solidification behaviors of Pt-containing 718Plus superalloys were studied by scanning electron microscopy(SEM),energy dispersive spectrum(EDS),differential scanning calorimetry(DSC)and simulation calculations.It is found that Pt increases solidification range and decreases solidus temperature of the alloy and precipitation temperature of Laves+ γ eutectic phase since Pt enlarges the region of γ phase by increasing Nb solubility.In addition,Pt segregates to the interdendritic region and increases the segregation of Nb and Ti in the interdendritic region due to the strong attractive interactions between Pt and Nb/Ti.As a result,Pt promotes the precipitation of the Laves+ γ eutectic phase andηphase around eutectic phase.The increase of solidification range and segregation degrees of Nb and Al caused by Pt also promotes the precipitation and growth of γ'+γ" phase around eutectic phase.These results provide experimental bases for understanding the mechanism of Pt in solidification behavior of superalloys.

Effect of Cooling Rate on the Solidification Behavior and Microstructure of SiC_w/Al-18Si Composites

Al-18Si alloy reinforced with 15%,20% and 25%(volume fraction) SiC whiskers were prepared by squeeze casting technique and the solidification behavior and microstructure of as-prepared composites at different cooling rates were studied by DSC,optical microscope,SEM and TEM.The results show that silicon phase is nucleated on SiC whiskers.With the increase of cooling rate,the degree of undercooling increases in the composites as well as in the alloys.The increase of cooling rate leads to a reduction in the size of eutectic Al-Si and also changes its morphology from short stick to equiaxed.However,the change of primary Si is complex.The primary Si size is refined,and then coarsened with increasing cooling rate.The primary Si morphology of composites changes from agglomerate to stick.

EFFECT OF GRAVITY FIELD ON SOLIDIFICATION BEHAVIOR OF STEEL INGOT

By means of numerical simulation. the in fluence of gravity on fluid flow,patterns has been simulated.The result shows that with the increase of inclined angle,the velocity of fluid flow decreases and the isotherms become flatter,which suppresses the evolution of channel segregation.

Solidification behavior of Re-and Ru-containing Ni-based single-crystal superalloys with thermal and metallographic analysis

To clarify the solidification behavior of Re- and Ru-containing Ni-based single-crystal superalloys, four experimental alloys with varied contents of Re and Ru were investigated by differential scanning calorimetry （DSC） and metallographic techniques. To obtain the - solvus temperatures, the stepwise solution and aging heat treatments were used. DSC analysis shows that Re leads to the increase in freezing range and γ-solvus temperature. On the contrast, Ru only has negligible influence on the freezing range, but leads to the lower γ-solvus temperature. In comparison with Ru, Re leads to more severe segregation and higher eutectic fractions in as-cast microstructures. Furthermore, the castability and phase stability of Ni-based superalloys were analyzed by the results of DSC and metallographic analysis, such as freezing range, critical nucleation temperature, γ-solvus temperature and eutectic fractions. It shows that Re leads to the wider freezing range and lower critical nucleation temperature, indicating the worse castability of Re-con- taining Ni-based single-crystal superalloys.

Recent progress on apparatus development and in situ observation of metal solidification processes via synchrotron radiation X-ray imaging: A review

The solidification process of metals plays a critical role in their final microstructure and, correspondingly, in their performance. It is therefore important to probe the solidification behavior of metals using advanced in situ techniques. Synchrotron radiation X-ray imaging is one of the most powerful techniques to observe the solidification process of metals directly. Here, we review the development of the solidification apparatus, including the directional solidification device, resistance furnace, multi-field coupling device, semisolid forming device, aerodynamic levitation apparatus, and laser additive manufacturing apparatus. We highlight the recent research progress on the use of synchrotron radiation X-ray imaging to reveal the solidification behavior of metals in the above circumstances. The future perspectives of synchrotron radiation X-ray imaging in metal research are discussed. Further development of this technique will contribute to improve the understanding of the solidification process of metals and other types of materials at different scales.

Effect of Zr on solidification and microstructure of a Ni-based superalloy with high Al and Ti contents

The total content of Al and Ti in advanced Ni-based wrought superalloys is up to 7.5wt.%,which makes it easier to form harmful nonequilibrium eutectic(γ+γ′)andηphase.It has been reported that the addition of certain amount of Zr can modify precipitation of the nonequilibrium phases obviously,but the mechanism is still controversial.The effect of Zr ranging from<0.0006wt.%to 0.150wt.%on solidification behavior,segregation and microstructure of a Ni-based superalloy with high Al and Ti contents was investigated,eliminating the interferences of C and B.Results show that increase in Zr content significantly promotes the formation of eutectic(γ+γ′),ηand Zr-rich phase in the interdendritic region.Besides the Zr-rich phase,Zr dissolves slightly in the eutecticγ′and obviously in theηphase.An interesting phenomenon is discovered that the Zr addition significantly increases the area fraction of liquid pools and enlarges the forming range ofγdendrites,which suggests that Zr markedly retards the solidification.Zr affects the eutectic(γ+γ′)andηformation mainly due to the retard of solidification and dissolution of Zr in them.The retard of solidification obviously increases the residual liquid fraction and undercooling.Zr can serve as a forming element for the eutectic(γ+γ′)andηphase,and the obvious dissolution of Zr inηphase significantly decreases the critical concentration of Ti for its precipitation.

A review of particulate-reinforced aluminum matrix composites fabricated by selective laser melting

Selective laser melting(SLM)is an emerging layer-wise additive manufacturing technique that can generate complex components with high performance.Particulate-reinforced aluminum matrix composites(PAMCs)are important materials for various applications due to the combined properties of Al matrix and reinforcements.Considering the advantages of SLM technology and PAMCs,the novel SLM PAMCs have been developed and researched in recent years.Therefore,the current research progress about the SLM PAMCs is reviewed.Firstly,special attention is paid to the solidification behavior of SLM PAMCs.Secondly,the important issues about the design and fabrication of high-performance SLM PAMCs,including the selection of reinforcement,the influence of parameters on the processing and microstructure,the defect evolution and phase control,are highlighted and discussed comprehensively.Thirdly,the performance and strengthening mechanism of SLM PAMCs are systematically figured out.Finally,future directions are pointed out on the advancement of high-performance SLM PAMCs.

The Innovative Model of Family Education Guidance of Guiding First,then Supplementing and Further Solidifying

In the new era a new more effective family education model can ease unbalanced and inadequate education development.In the new era,parents look forward to a more personalized,active and interactive form of family education guidance.This new guidance model will start with improving behavior by focusing on emotional behavior and cognition.The Roast can ease parents'anxiety,lectures and reading groups can supplement parents'knowledge,and mutual discussion,vicarious practice and teaching others can solidify a scientific and effective family education behavior.The family education guidance model of"guiding first,then supplementing and further solidifying"focuses on the participation of parents in the whole process,which can improve the effectiveness of family education guidance.

Melt flow,solidification structures,and defects in 316 L steel strips produced by vertical centrifugal casting

Vertical centrifugal casting can significantly enhance the filling capability of molten metals,enabling the production of complex thin-walled castings at near-rapid cooling rates.In this study,the melt flow,solidification structures,and defects in 316 L steel cast strips with a geometry of 80 mm×60 mm×2.5 mm produced by vertical centrifugal casting were numerically and experimentally analyzed under different rotation speeds.With gradually increasing the rotation speed from 150 r/min to 900 r/min,the simulated results showed the shortest filling time and minimum porosity volume in the cast strip at a rotation speed of 600 r/min.Since a strong turbulent flow was generated by the rotation of the mold cavity during the filling process,experimental results showed that a“non-dendritic”structure was obtained in 316 L cast strip when centrifugal force was involved,whereas the typical dendritic structure was observed in the reference sample without rotation.Most areas of the cast strip exhibited one-dimensional cooling,but three-sided cooling appeared near the side of the cast strip.Moreover,the pores and cracks in the 316 L strips were detected by computed tomography scanning and analyzed with the corresponding numerical simulations.Results indicated the existence of an optimal rotational speed for producing cast strips with minimal casting defects.This study provides a better understanding of the filling and solidification processes of strips produced by vertical centrifugal casting.

Ferrosilicon alloy granules prepared through centrifugal granulation process

A novel granulation process that involved the use of a rotary multi-nozzles cup atomizer and water cooling was proposed for ferroalloy manufacturing.The effects of rotating speed and nozzle diameter on the properties of FeSi75 alloy(containing 75 wt.%Si)granules were investigated.Results indicated that median granule diameter decreased as rotating speed in creased,and initially increased and then decreased as nozzle diameter in creased.The optimal conditi ons for the gra nulation of FeSi75 alloy were a rotating speed of 150 r/min and nozzle diameter of 10 or 12 mm.The phase composition,micromorphology,and elemental distribution of the FeSi75 alloy granules were also studied by X-ray diffraction,scanning electron microscopy,and energy-dispersive X-ray spectrometry.In order to provide guidance for the layout and water depth of the tank,the solidification behavior of ferrosilicon alloy droplet was numerically studied.A simplified model was established to elucidate the traveling trajectory and heat transfer of alloy droplet in air and cooling water during the atomization process.The solidification time of droplet with different thicknesses of solidification layer increased with the in crease in alloy droplet diameter.