Papers by Keyword: Semi-Solid Metal

Abstract: In order to investigate sub-rapid solidification behavior of semi-solid magnesium alloy metal, a novel semi-solid processing technique, called new vacuum suction casting (NVSC), is used to manufacture thin castings of AZ91D Mg-alloy directly from a liquid metal. The resulting microstructures of castings are characterized in detail and linked to the solidification behavior. In the microstructure of the sub-rapidly solidified SSM sheet, the “preexisting” primary solid particles, with the morphology of near-globules or rosettes, disperse in the homogeneous matrix consisting of fine near-equiaxed secondary α-Mg grains and fine precipitates of β-Mg₁₇Al12 intermetallics. Owing to rapid solidification rate, the volume fraction of the β phase in the sub-rapidly solidified SSM sheets is much lower than that in the as-cast ingot. In addition, the content of alloying elements of Al and Zn was higher in the grain boundaries and the eutectic structure than that in the primary solid particles and in the second α-grains.

Abstract: A computational model coupling electromagnetic stirring with a macroscopic heat and fluid flow in semisolid A357 alloy slurry preparation by A-EMS was developed. Effects of electromagnetic field on flow field and temperature field were presented successfully. It is shown that more intensive magnetic field, velocity field and thereby temperature field were uniformly distributed in the stirred melt even at commercial frequency, and thus more uniformly fine microstructures were obtained in comparison with normal EMS.

Abstract: CSIR-Rheo technology process which involves the preparation of metal slurry direct from liquid alloys by stirring and cooling was applied for treatment of Al-7%Si-0.35%Mg alloy, A356, to the Semi-Solid Metal state. Plates were cast in steel moulds with a 50 Ton High Pressure Die Casting machine. Heat treatments T4 and T6 were given to the samples. Butt laser welding was performed on the heat treated and as fabricated plates (F). Tensile properties, hardness profile, microstructure of the weld, heat affected zone and base metal were examined. Some comments on outcomes of the research are included.

Abstract: The preparation of semi-solid slurry of hypereutectic Al-Si alloy by Ultrasonic Vibration (USV) has been studied. The A390 alloy melt was poured into a preheated metal cup, and subsequently the ultrasonic vibrator was dipped into the melt and USV was imposed. The solidified microstructure of the slurry has been analyzed, and the mechanical properties of the alloy have been tested by making samples through diecasting of the slurry. The results show that the primary Si particles of A390 alloy became finer, rounder and uniformly distributed in microstructure of A390 alloy slurry if imposed with USV, and average diameter of primary Si particles was about 20μm. With USV, the ultimate tensile strength and the hardness of rheo-casted samples increased by over 25% and near 50% respectively besides the elongation rose by above 100%. After heat treatment, the mechanical properties were further improved. In addition, the mechanism of preparation of semi-solid slurry of hypereutectic Al-Si alloy by USV is discussed.

Abstract: The temperature fields during semi-solid magnesium alloy produced by casting-rolling technology has been simulated by finite element method on the basis of ANSYS. The temperature fields for different conditions were obtained, which is consistent with the experimental results. Results show that there is a high temperature field in the casting and rolling zone. The temperature fluctuates from the center to edge of the strip near the entry of the casting and rolling zone. but The temperature decreases gradually from the center to edge of the strip near the exit of the casting and rolling zone. There are some remarkable effects of the temperature of the casting and rolling, the velocity of the casting and rolling, the gap of two roll, the cooling of the roll and the diameter of the roll on the temperature field, which are in agreement with the experimental results.

Abstract: Magnesium alloys are increasingly used in automotive, aeronautic and electronic applications to produce high performance, light weight parts. In the thixomolding process the semisolid slurry is injected into a mold at controlled temperature such that the melt has specific flow behavior. This allows the fabrication of near net shape components with controlled microstructure and good mechanical properties. The numerical modeling of such applications presents unusual challenges for both the physical modeling and the solution algorithm. This paper presents 3D solutions of the injection molding of semi-solid AZ91 magnesium alloys. The methodology deals with the shear thinning, temperature dependent viscosity behavior and is able to accurately solve the high velocity flows encountered during semi-solid magnesium molding. The approach is applied to the injection of a tensile bar and the results compared with experimental data. The numerical solutions indicate that the material forms a jet at the exit of the gate and a swirling flow forms as the material advances along the first larger diameter section. The wall regions are filled first, leaving a void inside. This agrees very well with the experimental observation.

Abstract: An improved and self-developed semisolid preparing and rheomoulding device — rotating barrel rheomoulding machine (RBRM) for light alloys in laboratory is introduced in this paper. It mainly consists of a melting furnace, a shearing system with two relative-rotating conical barrels, a central temperature control unit, gas protection system and a die-casting system. Microstructure-processing relationship of A357 aluminum alloy obtained by the RBRM process is investigated by different intensity of turbulence and different shear rate. The experimental results show that the improved RBRM is capable of eliminating coarse dendrites, and producing small and spherical solid particles uniformly distributed in a eutectic matrix. In addition, the process can eliminate entrapped gas and reduce fine shrinkage pores in the specimens as well. Compared with the original self-developed device in our laboratory, the improved equipment has the following advantages: accurate control of stirring temperature; small volume and convenient manipulation; fine and spherical solid particles, chemical and microstructural uniformity throughout the specimens and so on.

Abstract: A simple and efficient rheocasting process that has recently been invented is being developed for aluminum die casting applications. The process called Gas Induced Semi-Solid (GISS) utilizes the combination of local rapid heat extraction and agitation achieved by the injection of fine gas bubbles through a graphite diffuser to create semi-solid slurry. In the GISS process, the die casting machine and the process cycle remain little changed from those of conventional die casting. The GISS unit creates a low solid fraction of semi-solid slurry in the ladle during the ladle transfer to the shot sleeve. The semi-solid slurry is then poured directly into the shot sleeve. This paper presents the detailed description of the process. The results of the semi-solid die casting experiments with ADC10 alloy using the GISS process are also reported and discussed.

Abstract: The mould-filling behavior of rheo-diecasting of semi-solid magnesium alloy and diecasting of liquid magnesium alloy has been simulated with the computer program of numerical simulation developed by the authors. Results show that, under the same diecasting conditions, the filling behavior of rheo-diecasting of semi-solid metals is similar to the liquid diecasting, but mould filling of semi-solid slurry is steadier, and the slurry flows into the mould in a state similar to lamellar flow. The air entrapment in semi-solid process is much smaller than that of liquid diecasting, and the castings made with semi-solid rheo-diecasting excel those with liquid diecasting in quality. Experimental results are in accord with the results of numeral simulation.

Abstract: Various processing methods exist for applying agitation to a molten metal during solidification to obtain metal slurries suitable for semi-solid metal processing. . In this paper, a new technique to achieve semi-solid metal structure using agitation during solidification is reported. The technique applies a new medium and means to efficiently create semi-solid metal structures. The results of a systematic study showing the feasibility and the necessary conditions to achieve the structure are discussed.