Microstructure Of Semi-solid Slurry Research Articles

Application of polarized light microscopy on microstructural characterization of semisolid slurry

In this paper, two ways of microstructural characterization, optical microscopy (OM) and polarized light microscopy (PLM), were both employed to describe the microstructure of semisolid slurry prepared by swirling enthalpy equilibration device (SEED). The results show that PLM is more reliable and accurate than OM to describe the special morphology feature of semisolid slurry made by SEED process. Meanwhile, the effects of pouring temperature and mass of molten liquid on the primary α-Al particle size and morphology were also investigated using PLM. The quantitative metallographic results measured from PLM demonstrate that the grain size and morphology and their distribution are significantly affected by both pouring temperature and the mass of molten liquid. The grain size poured with 2.7 kg liquid decreases from 659 to 186 μm, and grain morphology transforms from dendrite to globular structure with pouring temperature reducing from 690 to 630 °C. The decreasing pouring temperature also promotes the distribution of spherical structure on the cross section. Meanwhile, the mass of molten liquid decreasing from 2.7 to 2.3 kg can decrease the grain size by maximum of 44% at high pouring temperature.

Microstructure and Rheological Properties of Semi-Solid 7075 Slurries Using SEED Rheocasting Process

The SEED rheocasting process was used to produce semisolid slurries of high strength 7075 aluminum wrought alloys. The effects of the SEED processing parameters on the microstructure of semisolid slurries were studied. The impact of grain refinement on the grain morphology and size was investigated. The rheological properties of semisolid 7075 alloys were characterized at different solid fractions using a parallel plate compression viscometer. Results indicated that the grain refinement could greatly improve the globularity of α-Al grains and rheoformability. The relationships between viscosity and shear rate at different solid fractions in the transient state for both unrefined and refined semisolid slurries were evaluated and discussed.

Microstructure and Property of Rheo-Diecasting Magnesium-Alloy with Forced Convection Mixing Process

Taking AZ91D magnesium alloy as experimental material, the rheo-diecasting process was implemented by combining the self-developed forced convection rheomoulding device with high pressure die casting machine. Microstructural characteristics of the RDC tensile samples were discussed. Microstructure of semisolid slurry at different rotational speed prepared by FCR device was investigated. Tensile properties and fracture morphology of rheo-diecasting process in different conditions were studied as well. The results indicate that the excellent semisolid microstructure of AZ91D tensile samples can be obtained by forced convection rheo-diecasting process. With the increase of rotational speed, the mean size of the primary particles diminishes and the shape factor increases. The tensile properties of as-cast RDC samples are obviously better than conventional diecasting samples. T6 heat treatment can increase tensile strength and elongation of RDC tensile samples to 286MPa and 6.1%, respectively. The yield strength and elongation of T4 heat treated RDC samples are 100MPa and 12.6%.

Preparation and theoretic study of semi-solid Al2Y/AZ91 magnesium matrix composites slurry by ultrasonic vibration

Semi-solid Al2Y/AZ91 magnesium matrix composites slurry was prepared by ultrasonic vibration, effect of ultrasonic vibration temperature and time on microstructure of semi-solid slurry was investigated. The results showed that with the ultrasonic vibration temperature decreasing the solid volume fraction of semi-solid slurry increased. The best ultrasonic vibration temperature was 600 °C. With the increase of ultrasonic vibration time, the average grain diameter of primary a-Mg particles decreased firstly, then increased, the average shape factor increased gradually and decreased slightly after 90 s, and a few rosette dendrites were observed after 120 s. The best semi-solid slurry with average grain diameter of 75 μm and shape factor of 0.7 were gained after the melt was treated by ultrasonic vibration for about 60 s at near liquidus temperature (600 °C). At last, the microstructure evolution mechanism of semi-solid magnesium matrix composites slurry was analyzed by the theories of thermodynamics and kinetics.

Effects of Solid–Liquid Mixing on Microstructure of Semi-Solid A356 Aluminum Alloy

The desired starting material for semi-solid processing is the semi-solid slurry in which the solid phase is present as fine and globular particles. A modified solid–liquid mixing (SLM) is reported wherein semi-solid slurry can be produced by mixing a solid alloy block into a liquid alloy, and mechanical vibration is utilized to enhance the mixing. Effects such as liquid alloy temperature, mass ratio, and mixing intensity on the microstructure and the cooling curves during SLM were evaluated. 2D and 3D microstructure analysis of treated A356 aluminum alloy shows that microstructure can be refined significantly with a considerable morphology change in primary Al phase. It is critical that the temperature of mixture after mixing is lower than its liquidus temperature to obtain a valid SLM process. Specially, mixing intensity is identified as a primary factor for a favorable microstructure of semi-solid slurry.

Rheocasting of semi-solid Al359/20%SiC metal matrix composite using SEED process

A Duralcan Al359/20%SiC metal matrix composite was successfully cast using the SEED rheocasting process. Effects of the SEED processing parameters on the microstructure of semi-solid slurries and casting parts were studied. The parameters investigated in this study include pouring temperature, swirling time and swirling speed. The results showed that α-Al grains were nearly spherical and SiC particles were well distributed in both semi-solid slurries and cast parts when using the appropriate SEED parameters. The mechanical properties of the semi-solid cast components under as cast and T6 conditions were also investigated. Results revealed that a significant improvement of tensile properties was achieved when compared to the conventional gravity castings and those obtained from other semi-solid process.Le composite Duralcan Al359/20%SiC à matrice métallique a été moulé avec succès en utilisant le procédé de rhéomoulage SEED. L’effet des paramètres du traitement SEED sur la microstructure des pâtes semi-solides et sur les pièces moulées a été étudié. Les paramètres examinés dans cette étude incluaient la température de coulée, ainsi que la durée et la vitesse de rotation. Les résultats ont montré que les grains d’Al-α étaient presque sphériques et que les particules de SiC étaient bien distribuées tant dans les pâtes semi-solides que dans les pièces moulées lorsqu’on utilisait les paramètres appropriés de SEED. On a également examiné les propriétés mécaniques des composantes moulées semi-solides à l’état brut de coulée et sous la condition T6. Les résultats ont révélé une amélioration significative des propriétés de traction par rapport aux moulages conventionnels de coulée par gravité et par rapport aux propriétés obtenues avec d’autres procédés semi-solides.

Characterization of Flow Behavior of Semi-Solid Slurries with Low Solid Fractions

Semi-solid slurry casting is a metal-forming process that involves transforming liquid metal into slurry having a low solid fraction and then forming the slurry into solid parts. To successfully apply this slurry-forming process, it is necessary to fully understand the flow behavior of semi-solid slurries. This present work applied the rapid quenching method and the modified gravity fluidity casting to investigate the flow behavior, which involves characterizations of the initial solid fraction, fluidity, and microstructure of semi-solid slurries. Three commercial aluminum alloys were used in this study: 383 (Al-Si11Cu), 356 (Al-Si7MgFe), and 7075 (Al-Zn6MgCu) alloys. The results show that the initial solid fractions can be controlled by varying the rheocasting time. The rapid quenching mold can be used to determine the initial solid fractions. In this method, it is important to apply the correcting procedure to account for growth during quenching and to include all the solid phases. Results from the fluidity study of semi-solid slurries show that the fluidity decreases as the initial solid fraction increases. The decrease is relatively rapid near the low end of the initial solid fraction curves, but is quite slow near the high end of the curves. All the three alloys follow this trend. The results also demonstrate that the slurries that contain high solid fractions of up to 30 pct can still flow well. The microstructure characterization results show that the solid particles in the slurries flow uniformly in the channel. A uniform and fine microstructure with limited phase segregation is observed in the slurry cast samples.

Effect of Low-Voltage Electric Current Pulse on Semi-Solid Microstructure of Magnesium Alloy AZ91D

The effect of discharging cycle, voltage, capacitance and time on solidified microstructure of semi-solid slurry of AZ91D alloy treated with Low-Voltage Electric Current Pulse(LVECP) was investigated in this paper. The experimental results show that primary grains of AZ91D alloy were refined apparently, the morphology dendrites of α-Mg were changed by electric current pulse and the nondendritic structure of semi-solid slurry of AZ91D alloy could be obtained with appropriate processing parameters. The decrease of discharging cycle and the increase of discharging voltage and time to prepare semisolid slurry by LVECP discharge promotes the formation of fine α-Mg grains. It is proposed that LVECP treatment created a new dynamic factor for nucleation so that the number of nuclei increased, which restrained the formation of large primary α-Mg dendrites and created a base to form spherical crystals of primary α-Mg. The stronger temperature fluctuation in the melt with many rosette primary α-Mg caused by LVECP discharge and the remelting of the secondary arm roots in the same time are the most important reasons for formation of spherical primary α-Mg grains.

Preparation and rheocasting of semisolid slurry of 5083 Al alloy with indirect ultrasonic vibration process

Abstract The indirect ultrasonic vibration (IUV) method, in which the horn was vibrated under the outside of the metallic cup containing alloy melt, was employed for preparing semisolid slurry of 5083 Al alloy in this work. The effect of IUV on the microstructure of semisolid slurry and mechanical properties of rheo-diecasting samples were studied. The results indicate that good semisolid slurry could be obtained when the melt treated by IUV for 50 s, and the average diameter and shape coefficient of primary α-Al particles were 60 μm and 0.54 respectively. Apart from preparing semisolid slurry with fine microstructure, IUV had degassing effect on semisolid slurry of 5083 Al alloy. The tensile strength and elongation of the rheo-diecasting samples were 283 MPa and 9% respectively, which were increased by 11.4% and 32.4% respectively compared to conventional liquid die-casting samples.

Study on Microstructure of Semi-Solid Magnesium Alloy Manufactured by Gas Bubbles Stirring

The semi-solid slurry of AZ31 magnesium alloy was manufactured by gas bubbles stirring. The effects of stirring temperature and stirring time on the microstructure of semi-solid slurry were researched. The results indicate that it is feasible to manufacture the slurry with particle-like primary phases. When the stirring temperature is higher, the morphology of the primary a-Mg presents rosette-like morphology and the size of grain is coarse, and the morphology mainly was α- Mg dendrite at lower stirring temperature. Long stirring time could reduce dendrites and liquid phase, and made the non-dendritic grains well spheroidized. But the effects of longer stirring on shape and size of primary particles are not significant. The optimal process parameters for ideal semi-solid slurry manufactured were stired 3min at 645°C.

Semi-Solid Processing Technologies of Magnesium Alloys

Magnesium alloys are becoming more and more attractive because of their low density, high specific stiffness and strength, good heat conductivity, high electromagnetic interference shielding and damping capabilities, etc. Magnesium alloy components produced by semi-solid processing (SSP) has the merits of high dimension stability and quality. Moreover, it is desirable to apply the SSP technology to produce components free of gas holes and porosity which are usually found in those produced by the die casting. SSP of magnesium alloys has been utilized in Japan and Taiwan, China. In this paper, preparing methods of semi solid slurry appropriate for magnesium alloys are introduced, including stirring, SSIT-semi solid isothermal heat treatment, pouring temperature controlling, grain refinement and so on. The effects of process parameters on the microstructure of semi-solid slurry are also discussed. In addition, thixomolding technology practically utilized in the semi-solid processing of magnesium alloys is also introduced. At last the prospect of Semi-solid processing technologies for magnesium alloys are discussed.

Performance of semi-solid slurry produced by twin-screw stirring mixer and rheo-diecasting process of AZ91D alloy

The microstructure of semi-solid slurry of AZ91 D alloy, which was produced by twin-screw stirring mixer under the different parameters, was investigated. Rheoforming by cold chamber die casting process was performed thereafter. The results indicate that with decreasing of the barrel temperature of the mixer and the pouring temperature of molten Mg alloy, the solid fraction of semi-solid slurry increases and the size of non-dendritic grains becomes smaller. While the shear rate increases, the solid fraction of semi-solid slurry decreases. The tensile strength and elongation of metal rheoformed by die casting are higher by about 37% and 44% respectively than those produced by conventional liquid die casting.