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.     

SSM过程模拟仿真技术

介绍了模拟仿真技术在半固态金属成形 (SSM )中的研究现状 ,展望SSM过程模拟仿真技术的发展趋势。     

半固态金属铸造的新进展——注射成形

介绍了半固态金属铸造的最新发展趋势———注射成形 ,它将塑料的注射成形原理应用于半固态金属铸造中 ,集半固态金属浆料的制备、输送、成形等过程于一体 ,较好地解决了半固态金属浆料的保存输送和成形控制等问题。通过简述几种半固态金属注射成形工艺方法的原理及特点 ,试图展示半固态金属铸造技术工程应用的关键及发展方向     

大型铝合金铸件（轮圈）的半固态成形技术

半固态金属的组织及流变特性,早在1971年就被美国麻省理工学院（MIT）的Flemings教授所指导的研究团队,在进行实验时偶然间所发现。但半固态铝合金商业应用的产品,除了美国AEMP及瑞士Buhler公司分别拥有及发表铝轮圈的半固态成形技术之外,大部分仍停留在中小型铸件的生产。为了适应汽车轻量化需求,由作者的服务单位与（台湾）工业技术研究院所合组的研究团队,在历经约三年的合作,从半固态触变铸造（Thixocasting）的球化坯料（slug）、再加热技术至流变铸造（Rheocasting）的半固态浆料（Slurry）,进行了多项实验,最终验证了半固态技术应用于大型铝合金铸件（轮囤）生产的可行性。自2005年起,使用A356合金材料改良流变铸造法及2700t的实时射控压铸机的生产线,成功产出汽车用大尺寸半固态铝轮圈,并获得较传统铸造为佳的力学性能,有效达成零部件轻量化需求。     

半固态金属成形应用的新进展与前景展望

论述了半固态金属坯料制备工艺、成形工艺、半固态金属成形件的性能和半固态金属成形在一些发达国家应用的最新进展,并展望了半固态金属成形在我国应用的前景及意义。     

Direct thermal method: new process for development of globular alloy microstructure

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     

Combined grain refining and modification of conventional and rheo-cast A356 Al–Si alloy

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.     

Microstructure and material soundness in liquid and rheocast AM50 and effect of section thickness

Commercial grade AM50 magnesium alloy was diecast to varying wall thickness using both the RheoMetal process and conventional liquid casting. The resulting microstructure and pore structure were analysed. The rheocast material had larger pores than the conventionally cast material, scattered over the central 50% of the cross-section, while the pores in the conventionally cast material was concentrated to a segregation band at a depth corresponding to approximately 30% of the wall thickness. In the Rheocast samples, there was a correlation between thicker sections and larger primary α-Mg globules with a lower shape factor.     

Effects of rheocasting and heat treatment on microstructure and mechanical properties of A356 alloy

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.     

Micromechanics based modelling of deformation behaviour of grain refined rheocast Al–7Si–0.3Mg alloy

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.