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. 相似文献
This paper describes a comprehensive study on the combined addition of Ti–B grain refiner and Sr modifier elements to A356 Al–Si alloy. Using different qualitative and quantitative techniques in conventional and semi-solid metal castings, it is shown that, while the refiner and modifier elements affect respectively the nucleation and eutectic reactions, the combined addition not only replicates both individual element effects but also gives the added bonus of better globularity in the semi-solid metal process. A new innovative concept is introduced for fluidity measurement by using the magnitude of remaining liquid in the form of drainage, which is increased by combined treatment. 相似文献
Semisolid metal processing (SSMP) is of growing industrial significance particularly for magnesium and aluminium alloys. SSMP requires a binary micro-structure in which the primary phase is approaching a spheroidal (globular or non-dendritic) shape. Traditionally this is achieved by stirring the alloy in the mushy state. An alternative method, which is gaining popularity, is the so-called slurry-on-demand or new rheocasting process in which solidification conditions are controlled via active thermal management to yield non-dendritic solid in a liquid matrix. The authors present here a novel low-cost process, the direct thermal method (DTM), in which a globular microstructure, suitable for SSMP, is achieved via the naturally occurring thermal environment in a very simple casting experiment. Basically the DTM is a process in which liquid alloy of low superheat is poured into a cylindrical metallic mould of very low thermal mass but high thermal conductivity. Heat-matching between alloy and mould results in a pseudo-isothermal hold within the solidification range of the alloy, made possible by the very low rate of heat loss to the environment. Without the use of any special insulation or heating devices, the fraction solid during the experiment and the hold time can be modified by simple alterations to the process variables and geometry. The thin mould walls also make quenching easy. The resultant alloy morphology is characterised for an aluminium alloy designation A356. IJCMR/463 相似文献
The effects of the rheocasting process and T5 heat treatment on microstructure and mechanical properties of A356 alloy were investigated. The results show that the temperature range for the solid-liquid state is roughly between 560 °C and 630 °C, and the solid fraction increases from 0% to 100% with decreasing temperature. The finer microstructure in rheocasting in comparison with the one in conventional casting was attributed to pressure breaking down the secondary dendrite arms, especially for specimens around 600-610 °C. It was proved that rheocasting specimens have improved mechanical properties over the conventional casting ones. Furthermore, the result shows that T5 heat treatment can strengthen A356 alloy, while the plasticity was reduced at the same time. 相似文献
Microscale deformation behaviour, plastic strain localisation and plastic instability of grain refined rheocast Al–7Si–0.3Mg alloy have been studied here, following micromechanical approach. Micromechanics based simulations have been performed by means of the two-dimensional representative volume element of the actual microstructure, using the popular finite element (FE) package ABAQUS. The molten alloy has been rheocast after grain refiner addition, using cooling slope, and comparison has been made with its conventional cast counterpart. Effect of grain size, shape and its orientation on microlevel stress/strain state of the material, before the final failure, has been predicted in the present study. Increasing uniformity in stress and strain distribution at the microscale has been evidenced with the increasing sphericity and volume fraction of the primary Al phase. 相似文献
Understanding the flow behavior of semi-solid slurries containing low solid fractions is key to the success in applying this process in the die casting industry. With these low initial solid fractions, the flow behavior of semi-solid slurries is quite complicated, making it difficult to model accurately. This present work developed and studied characterization methods for the flow behavior of semi-solid slurries at low solid fractions in high-pressure die casting. A new parameter, the ratio of gate speed to initial solid fraction (Vg/fs), was proposed to be correlated to the normalized flow interface length, blister area and tensile properties. Results from the flow pattern analysis suggest that the flow behavior can be controlled to achieve laminar flow by varying the initial solid fraction. Blister test results show the trend that slurry die casting conditions with high Vg/fs values exhibit high blister areas. Die casting conditions with excessively high gate speeds and insufficient solid fractions result in turbulent flow patterns and high levels of blister defect. The results of tensile test and fracture surface analysis are consistent with other analysis results. The samples formed by liquid die casting and slurry die casting with high Vg/fs values have gas porosity due to turbulent flow pattern during die filling. On the other hand, the samples formed by slurry die casting with too low Vg/fs values contain shrinkage porosity. This is because of insufficient time for shrinkage feeding due to a combination of a high solid fraction and a low gate speed. This study has demonstrated that die casting with slurries containing low initial solid fractions gives die casters another process parameter to adjust, which can help reduce and control the gas and shrinkage porosities. 相似文献