Papers by Keyword: Solid Fraction

Abstract: It is known that ultrasonic waves promote nucleation and globulization of solid particles in aluminium alloys. However, the studies performed up to date have been conducted, in the laboratory, using small volumes of aluminium. This article aims to establish the application of ultrasound effect in the A357 aluminium-silicon alloy in amounts of about 2 kg of material. The experiments have been conducted with different parameters of ultrasonic treatment, evaluating the microstructure of the slurry quenched from the semi-solid state. The globulization effect of aluminium α phase by ultrasounds is very effective in the area close to the ultrasonic horn tip and the transmission system, but its effect highly reduces in the regions far away from the source of ultrasonic waves.

Abstract: The lost foam casting (LFC) process utilizes the expanded polystyrene (EPS) foam pattern for the production of metallic components. The thermal degradation of the foam pattern has a significant effect on microstructure of the component. Dendrite coherency is important for the determination of the formation of the solidification structure and cast ability of alloys. The effects of the dendrite coherency on grain size in Mg-4Al alloy have been studied using the two-thermocouple thermal analysis technique in the solidified sample. The results also indicate that the grain size increases with the temperature interval between liquids (T_N) and dendrite coherency point (T_DCP), The solid fraction at DCP (f_s^DCP) expressed in percent strongly dependents on the dendrite morphology during solidification.

Abstract: Taking the 7075 aluminum alloy as an example, this paper did some simulation work on temperature, flow field and shrinkage porosity distribution in the rheocasting process using the simulation casting software PROCAST. Effects of the casting temperature and filling speed on casting quality as well as segregation phenomenon of solid and liquid phases were discussed in this paper. Proper ranges of casting temperature and filling speed were obtained by the simulation. Good quality parts without shrinkage porosity were obtained in validation test using the casting temperature of 622~625°C and filling speed of 40mm/s. Rheocasting was an important forming method using semi-solid melt to manufacture metal parts directly. It was a promising trend of semi-solid forming industry which had shorter process, higher efficiency and lower energy consumption compared to SIMA method [1-4]. Rheocasting was generally applied to casting aluminum alloy but seldom to wrought aluminum alloys. The 7xxx series aluminum was generally manufactured though wrought or rolling technique to obtain dense parts with high strength. But few of them were produced directly through casting method without casting flaws[5-6].To process the 7xxx series aluminum by rheocasting method would further expand the application of wrought aluminum alloy, so it is essential to do some research on the rheocasting technique for wrought aluminum alloy. Taking the 7075 aluminum alloy as an example, this paper did some simulation work on temperature, flow field and shrinkage porosity distribution in the rheocasting process using the simulation casting software PROCAST. The effects of casting temperature and filling speed on the casting quality as well as the segregation phenomenon of solid and liquid phases were discussed in this paper. Proper ranges of casting temperature and filling speed were obtained by the simulation.

Abstract: We have developed new type semi-solid injection process, that is, runner-less injection process which can obtain high material yield of about 90% for magnesium alloy. In this process, alloy billets are heated to the semi-solid temperature in the injection cylinder and are injected into a permanent mold. In order to investigate the effects of volume fraction solid and injection speed on microstructure and mechanical properties of AZ91D magnesium alloy injected into the permanent mold, semi-solid forming testing machine which has the same system as a runner-less injection machine, has been made on an experimental basis. The magnesium billet precisely controlled at given temperature has been injected into a permanent mold with two kinds (slow and high) of speed and plate-like specimens with each fraction solid have been fabricated. Microstructure has been observed by optical microscopy and X-ray computerized tomography (CT) scanner. Mechanical properties have been measured by tensile test. The effects of volume fraction solid of the alloy slurry and injection speed on mechanical properties have been clarified.

Abstract: Thixoforging involves shaping alloys with a globular microstructure in the semi-solid state. To reach this kind of material, the Recrystallisation and Partial Melting (RAP) process can be used to obtain a globular microstructure from extruded material with liquid penetrating the recrystallised boundaries. Induction heating is used to apply the RAP process to slugs. One of the benefits of using this method of heating is the fast heating rate (20°C/s). This paper will help to improve heating parameters by showing their influence on 7075 aluminium alloy recrystallisation. These parameters are the heating rate; heating frequencies-power; presence or not of protective gas; position of the slug in the inductor; energy stored inside the slug; oxide layer on the slug side; chamfer of the slug upper corner.

Abstract: Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5

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