Effect of Pouring Temperature by a Novel Micro Fused-Casting on Microstructure and Properties of ZL101 Semisolid Slurry

A novel micro fused-casting(MFC)process is developed for semisolid aluminum alloy slurry.The microstructure evolution and properties of semisolid ZL101 aluminum alloy slurry with difierent pouring temperature by MFC are investigated in this paper.During the cooling process,the effects of the pouring temperature on microstructure and properties is primarily analyzed.The microstructure of the semisolid ZL101 aluminum alloy is more homogeneous and the grain is smaller under proper pouring temperature.Temperature of liquids and solids of ZL101 aluminum alloy is measured by difierential scanning calorimetry(DSC).Distribution and characteristics of the microstructure of samples are examined by optical microscope(OM),scanning electron microscopy(SEM)equipped with energy dispersive spectrometer(EDS).The results show that the ZL101 semisolid slurry fabricated by MFC presents uniform shape and good grain size under the pouring temperature of 594°C and the stirring velocity of 600 r/min,and the fine grains of the primary a-Al phase with average grain size of 55μm and shape factor up to 0.67 were obtained.Besides,the ultimate tensile strength and the average Vickers hardness for semisolid ZL101 aluminum slurry are 178.19±1.37 MPa and 86.15±1.16 HV,respectively.

Mold-filling ability of semisolid alloy

The mold-filling ability of the semisolid alloy has very important effects onthe quality and properties of the work pieces produced by the semisolid forming process. Thefactorial experiments show that all of the heating factors, such as mold temperature, heatingtemperature and the keeping time of billets, have some effects on the mold-filling ability ofsemisolid alloy. According to the analysis of influencing extent on the filling ability, it is foundthat the most important one of the factors is the mold temperature instead of the billetstemperature, the next one is the heating temperature of the billet, and the keeping time rows on thethird. It is also found that there is an interrelation between the billet heating temperature andthe mold temperature. The effect of the interrelation on the mold-filling ability is even strongerthan the keeping time. The higher the mold temperature, heating temperature or the keeping time is,the better the mold-filling ability of the semisolid alloy is. The parameter to describe themold-filling ability, defined as the maximum filling height along the uptight direction or themaximum filling length along the horizontal direction, can be theoretically determined according tothe flowing theory of viscous fluid.

Efficient fabrication of semisolid nondendritic Al alloy slurry with high quality

Subjecting a normal mechanical vibration to a cooling slope plate,is a proposed method for preparing semisolid nondendritic slurry,named shear-vibration coupling sub-rapid solidification(SCS).Taking Al-8Si alloy as model material,the temperature field and distribution field of solid or liquid phase during SCS were simulated using COMSOL Multiphysics software to primarily choose the optimal processing parameters.Subsequently,the slurries were prepared with the parameters selected according to the simulation results and the microstructures of the slurries were experimentally investigated.Results indicate that the simulation results could provide a basis for roughly choosing the processing parameters,although the calculated solid fractions are always higher than the experimental ones.The processing parameters affect the primary grain size,shape factor and solid fraction mainly through altering the contact duration of melt on the plate,and thus affecting the cooling effect on the melt,nucleation rate,and grain dissociation and proliferation.Experiments with optimized processing parameters show that the primary grains in the slurry have an average size of about 32μm and shape factor of 1.38,and are quite uniform,even at the highest pouring rate of 2.81 kg·s^(-1),the size and shape factor are about 46μm and 1.7,respectively,which implies that the proposed SCS is a promising technology for efficient fabrication of high-quality Al slurry available for engineering applications.

Grain Size Control of Semisolid A356 Alloy Manufactured by Electromagnetic Stirring

To investigate the possibility of substituting the mechanical stirring system with electromagnetic stirring (EMS) system for aluminum rheo die-casting, the EMS under the different stirring cooling conditions was carried out. It was found that in the early period of solidification, the dendrite breakages led to a fine primary phase. When dendrites grew coarsely, the effect of ripening on grain size overwhelmed that of dendrite breakage. It was also found that the high cooling rate favored large nucleation rate, and led to a fine primary phase. But high cooling rate also made the growth rate of the dendrite arm, which prevented the dendrite arm from being sheared off. Therefore there were a suitable stirring time and suitable cooling rate to obtain the best rheo die-casting structure. Qualified semisolid A356 aluminum alloy was successfully manufactured with short time EMS.

Numerical simulation on electromagnetic field,flow field and temperature field in semisolid slurry preparation by A-EMS

A two-dimensional computational model coupling an annular electromagnetic stirring（A-EMS） with a macroscopic heat and fluid flow analysis in Al-alloys semisolid slurry preparation was developed.The dynamic evolutions of the electromagnetic field,flow field,and temperature field were presented successfully by commercial software ANSYS 10.0 with corresponding experimental verification.A horizontally rotational electromagnetic field and,thereby,a more intensive velocity field were uniformly distributed in the stirred melt even at commercial frequency,and thus,a lower temperature difference in the stirred melt and subsequent uniformly fine microstructures were obtained compared with the normal electromagnetic stirring.The simulation results were in good agreement with experimental ones.

Continuously extending extrusion forming of semisolid A2017 alloy by SRS process

A self-made single-roll stirring (SRS) machine was used to manufacturesemisolid A2017 alloy, the mechanism of A2017 alloy formation was investigated. It was shown thatA2017 dendrites growing on the rough roll surface are crashed into fragments by the roll, which moveand grow freely then contribute the formation of finer spherical microstruc-ture. When casting at710-750℃, fine and homogeneous spherical or elliptical grains of A2017 alloy were obtained.Extending forming mould has been designed and was installed at the exit of roll-shoe gap. A2017alloy was formed by extending continuously at the semisolid state on SRS machine. Throughcontrolling pouring temperature, semisolid forming and extending extrusion was combined organically.A2017 product with fine surface and rectangular transection of 14 mm x 25 mm was obtained. Bycontrast to the national standard, the fracture strength and elongation of A2017 products producedfrom extending semisolid extrusion have been improved with an increase of 100 MPa and 29%,respectively.

Dynamical Solidification Behaviors and Metal Flow during Continuous Semisolid Extrusion Process of AZ31 Alloy

In this paper, a novel near-net-shape forming process, continuous semisolid extrusion process （CSEP） of AZ31 alloy was proposed, and the dynamical solidification behaviors and metal flow during the process were firstly investigated. During casting AZ31 alloy by this process, non-uniform microstructure distributions and non- equilibrium solidification region near the roll surface were found in the roll-shoe gap. Microstructural evolution from dendrite to rosette and spherical grains was observed during the casting by CSEP. Casting temperature, roll-shoe gap width and cooling ability have great effect on casting process and metal flow, so these factors should be carefully controlled, a proper casting temperature of 710-750℃ is suggested. The white α phases were strongly stretched during the processing, and the remnant liquids are correspondingly distributes along the solid phase boundaries and also show stripped lines.

Microstructure Evolution during Solidification of AZ91D Magnesium Alloy in Semisolid

The liquid quenching method was adopted to study the solidification morphology and microstructure of AZglD Mg alloy in semisolid. The results indicate that cooling rate has important effects upon the solidification structures. Under the cooling rate of liquid quenching, primary α-phase grows first by attaching on the original α grains, or independent nucleation and growth. The high cooling rate makes primary α-phase grow in ＂rags＂ or dendrite shape. Eutectic solidification is carried out in terms of both dissociated growth and symbiotic growth. The dissociated growth forms rough and large β-phase at grain boundaries, while symbiotic growth forms eutectic of laminar structure. The small liquid pool inside the original α-phase solidifies basically in the same way as that of intergranular liquid, but owing to less amount of liquid phase, the eutectic solidification is mainly carried out in the dissociated pattern.

Effects of casting factors of cooling slope on semisolid condition

The effects of the casting factors such as nozzle size to pour the melt,nozzle height,tilt of the slope and slope length,of the cooling slope on the process to make semisolid slurry were investigated.The results show that these factors affect the behaviors of the semisolid slurry on the cooling slope.The tilt of the slope is the factor that has major influence on the behavior of the semisolid slurry.The cooling roll is developed from the result of the research of the cooling slope.The rotating cooling roll can improve the sticking of the semisolid slurry on the substrate and it is suitable for making the semisolid slurry.

Preparation of semisolid AlSi7Mg alloy slurry through weak traveling-wave electromagnetic stirring

The semisolid AlSi7Mg alloy slurry with large capacity was prepared by low superheat pouring and week traveling-wave electromagnetic stirring. The effects of electromagnetic stirring power and frequency on the shape and distribution of primary α-A1 grains in the AlSi7Mg alloy slurry were discussed. The experimental results show that the AlSi7Mg alloy slurry with fine and spherical primary α-A1 grains distributed homogeneously can be obtained. Under the condition of low superheat pouring and week traveling-wave electromagnetic stirring, when the pouring temperature is 630℃, raising the stirring power or frequency appropriately can gain a better shape of primary α-Al grains; but if the stirring power or frequency is increased to a certain value （1.72 kW or10 Hz）, the shape of primary α-A1 grains cannot be obviously improved and spherical primary α-Al grains distributed homogeneously can be still obtained.

Stability condition of semisolid continuous casting process

The major unsteady phenomena in semisolid continuous casting process are the breakage and breakout. The essential reasons for them are the passageway blocking or the solidified shell too thin to endure the withdrawal force because of the remained shell formed at the beginning and its developing afterwards. Through theoretically analyzing the crack filling and the remained shell developing, stability conditions were presented. The essential one of them is that the stress acted on the semisolid slurry must be larger than the yield stress of it. The condition without breakage is to build a balance between the increase of the remained shell resulted in solidifying and the decrease of it resulted in flowing of the semisolid slurry. The condition without breakout is to ensure the solidified thickness larger than the safe thickness. The corresponding mathematical formulas of these conditions were set up and the verification experiments show that these conditions are reliable in applications. [

Semisolid A356 alloy feedstock poured through a serpentine channel

Fine spheroidal and equiaxed nondendritic microstructures required for semisolid casting can be formed through a serpentine pouting channel. Effects of the pouring temperature and the vertical section length of the serpentine pouring channel were studied. The results indicate that both favorable semisolid microstructures of A356 aluminum alloy can be generated by a serpentine pouring channel, and the solid shell inside the channel can be avoided when the pouting temperature is in the range from 660 to 680℃. It is also shown that the vertical section length of the serpentine pouting channel has a significant influence on the microstructure of the feedstock, namely both the microstructure of the feedstock and the microstructure uniformity in the radial direction get worse when the vertical section length is shortened; moreover, the pouring temperature for obtaining the feedstock with suitable microstructure decreases. The relevant mechanisms were discussed.

Characterization on morphology evolution of primary phase in semisolid A356 under slightly electromagnetic stirring

The effects of slight electromagnetic stirring on morphology of primary phase in semisolid A356 prepared by low superheat pouring and slight electromagnetic stirring were researched,and some characteristic parameters characterized the morphology and grain size of the primary phase were calculated.The results indicate that the stirring power has an important effect on the morphology and the grain size.The characteristics of the morphology could be characterized by the fractal dimensions and the shape factors.The fractal dimension and the shape factor change when the morphology changes with processing conditions.Both increase with the increase of the stirring power,but the fractal dimension is still affected by the grain size.The increase of stirring power could obviously improve the grain size,fractal dimension and shape factor of the primary phase.

Mechanical properties of hypereutectic Al-Si alloy by semisolid processing

Semisolid hypereutectic Al Si alloy billets were obtained by electromagnetic stirring, in which microstructure of primary silicon gets rounder and there are a large number of rosette α phases appearing. Compared with conventional gravity die casting alloys, the tensile strength and elongation of semisolid forming hypereutectic Al Si get obviously improved. Change of primary silicon morphology of semisolid hypereutectic Al Si alloy made by electromagnetic stirring is the main reason of better tensile strength, and a large number of rosette α phases precipitation is the main reason of better elongation.

Effect of high shear rate on solidification microstructure of semisolid AZ91D alloy

To investigate the effects of rotation speed and shearing time on morphology of semisolid AZ91D alloy,experimental work was undertaken using a twin-screw slurry maker.The results show that increasing the rotation speed and reasonable time can give rise to substantial grain refinement during continuous shearing stage,which can be attributed to the increasing of effective nucleation rate caused by the extremely uniform temperature due to high shear rate and high degree of turbulence.Comparing with low rotation speed at the same thermal condition,the analysis indicates that the microstructures obtained at high rotation speed are homogenous spherical and fine grains instead of dendritic or rosette and exhibits uniform distribution in the eutectic matrix.

Effect of Pouring Temperature on Microstructure and Properties of A356 Alloy Strip by a Novel Semisolid Micro Fused-Casting for Metal

A novel semisolid micro fused-casting(MFC) for preparing A356 alloy strips is proposed, and the effects of process parameters of pouring temperature on the microstructure and properties of A356 alloy strips are investigated. MFC means that the semisolid metal slurry was pressed out from the outlet of bottom of crucible to the movable plate, and directly solidified and formed layer by layer. The microstructure and properties of A356 semisolid alloy slurry were influenced by the cooling conditions. Results show that the aluminu alloy A356 strip samples fabricated by micro fused-casting had good performances and uniform structures with the pouring temperature at 595 ℃ and the substrate movement speed at 18 mm/s. The fine grains of the primary a-Al phase with average grain size of 53 μm and shape factor up to 0.72 was obtained, the ultimate tensile strength of the aluminum alloy A356 strip reaches 243.79±3.91 MPa, while the average vickers hardness is 82.65±1.86 HV.

Microstructure and properties of A2017 alloy strips processed by a novel process by combining semisolid rolling,deep rolling,and heat treatment

A novel short process for producing A2017 alloy strips with notable features of near net shape, saving energy, low cost, and high product performance was developed by combining semisolid rolling, deep rolling, and heat treatment. The microstructure and properties of the A2017 alloy strips were investigated by metallographic microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, tensile testing, and hardness measurement. The cross-sectional microstructure of the A2017 alloy strips is mainly composed of near-spherical primary grains. Many eutectic phases CuA12 formed along primary grain boundaries during semisolid rolling are crushed and broken into small particles. After solution treatment at 495℃ for 2 h the eutectic phases at grain boundaries have almost dissolved into the matrix. When the solution treatment time exceeds 2 h, grain coarsening happens. More and more grain interior phases precipitate with the aging time prolonging to 8 h. The precipitated particles are very small and distribute homogenously, and the tensile strength reaches its peak value. When the aging time is prolonged to 12 h, there is no obvious variation in the amount of precipitated phases, but the size and spacing of precipitated phases increase. The tensile strength of the A2017 alloy strips produced by the present method can reach 362.78 MPa, which is higher than that of the strips in the national standard of China.

Effect of partial remelting time on the initial carbide in semisolid structure of hypereutectic high Cr cast iron

In order to review the effect of partial remelting time on the morphology of initial carbides, semisolid ingots of hypereutectic high Cr17 cast iron were remelted at 1270℃ for four different times, and the changing characteristics of shape factor and the equivalent diameter of initial carbides were analyzed quantitatively using a Leica image analyzer. The results indicate that firstly, the evolution process of the initial carbides' morphology undergoes melting, spheroidization and refining during the partial remelting; secondly, the solute diffusion and interface tension take dominant roles at the primary and the middle-final stages respectively in the process of initial carbide evolution; finally, a perfect structure can be obtained by remelting semisolid ingots at 1270℃ for 15 min.

Preparation and mechanical properties of SiC/2024 composite by semisolid casting

A SiC/2024 composite was made by semisolid casting. The wetting between SiC and Al matrix is improved by treating SiC particles at a high temperature, coating K2ZrF6, and adding Mg to the Al melt. An effective way to remove the gas around SiC particles was also found. Microstructures were observed under optical microscope (OM) and scanning electron microscopy (SEM). The results show that SiC particles and Al matrix are well bonded and no gaps or cavities around the particles are observed. SiC particles distribute homogeneously in the Al matrix. The existence of SiC particles results in the increase of wear resistance and strength.