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Semisolid casting of aluminium alloys is growing. For magnesium alloys, Thixomoulding became the dominant process around the world. For aluminium processing, the situation is different as semisolid processing of aluminium is more technically challenging than for magnesium. Today three processes are leading the process implementation, The Gas-Induced Superheated-Slurry (GISS) method, the RheoMetal process and the Swirling Enthalpy Equilibration Device (SEED) process. These processes have all strengths and weaknesses and will fit a particular range of applications. The current paper aims at looking at the strengths and weaknesses of the processes to identify product types and niche applications for each process based on current applications and development directions taken for these processes.

The biggest challenge in semisolid processing of high-performance aluminum alloys is the narrow temperature processing windows of these alloys, and as a result, the preparation of qualified semisolid slurries is very important. High solid fraction slurries of high-strength A201 alloy were prepared by the Swirled Enthalpy Equilibration Device (SEED) process. The cooling behavior and microstructures of the A201 slurries produced by the standard, as well as a modified, SEED process were investigated. The results show that qualified A201 slurry can be produced by decreasing the pouring temperature and controlling the processing time in the SEED process. The modified SEED process significantly reduced the radial temperature gradient of the melt, due to the slow cooling rates involved, with the resulting slurries being more uniform, with more spherical microstructures, as compared to those produced by the standard SEED process. The formation of the nondendritic grain structure in the SEED process is attributed to the uniformly distributed large number of nuclei within the melt and the slow cooling of the melt in the containing crucible.

Abstract: 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. [Copyright &y& Elsevier]

Abstract: A comprehensive study was carried out to establish the effect of melt treatment using Ti–B grain refiner and Sr modifier additions on the microstructural evolution and rheological properties of A356 aluminum alloy in the semisolid state. Rheocast billets of 75mm in diameter and ∼140mm in length, prepared by the SEED process, were deformed and several parameters were investigated to characterize the flow behavior of the billets in a compression test. Strain–time graphs were used to calculate the viscosity and liquid segregation was monitored to identify the optimum conditions for melt treatment. It is shown that non-treated alloy has the highest apparent viscosity. Refined semisolid billets have smaller particle size and more globularity of primary α-Al particles and as a result deform and flow more easily. It is postulated that modifier addition reduces the liquid surface tension and leads to improved deformability. [Copyright &y& Elsevier]

Abstract: The effect of inoculation has been studied on the microstructural evolution in conventional and semi-solid-metal (SSM) processing of A356 Al–Si alloy. It has been found that small additions of Ti–B shift the liquidus temperature up and the recalescence decreases. The nucleation event takes place at higher temperatures. Furthermore, the rate at which growth temperature increases is less than that of nucleation temperature and therefore more nuclei form with less potential for growth. In SSM processing refiner increases the α-Al percentage and reduces globule size. Improvement of primary particles’ sphericity and globule size reduction are the main advantages of refiner addition. [Copyright &y& Elsevier]

Abstract: Silicon is one of the most significant alloying elements incorporated in Al-alloys. Its addition is to improve castability, fluidity, reduce shrinkage and to render superior mechanical properties. The morphology of silicon however plays an important role on the mechanical properties of finished products. Therefore, the common practice is to modify the as-cast flake or acicular silicon morphology employing special heat treatment or addition of certain modifiers. As a result, the silicon morphology changes to fibrous form with enhanced mechanical properties of the as-cast parts. For conventional casting, Si modification has been investigated widely by many researchers but in the semi-solid metal (SSM) processing, few published papers could be found. The purpose of this contribution is to report the effects of Sr addition as a modifier to 356 alloys for both conventional and SSM casting routes. The swirled enthalpy equilibration device (SEED), slurry-on-demand process was used to cast SSM billets. A comprehensive set of data is presented to characterize microstructural evolution of the as-cast SSM billets. [Copyright &y& Elsevier]

Semisolid casting of aluminium alloys is growing. For magnesium alloys, Thixomoulding became the dominant process around the world. For aluminium processing, the situation is different as semisolid processing of aluminium is more technically challenging than for magnesium. Today three processes are leading the process implementation, The Gas-Induced Superheated-Slurry (GISS) method, the RheoMetal process and the Swirling Enthalpy Equilibration Device (SEED) process. These processes have all strengths and weaknesses and will fit a particular range of applications. The current paper aims at looking at the strengths and weaknesses of the processes to identify product types and niche applications for each process based on current applications and development directions taken for these processes. [ABSTRACT FROM AUTHOR]

The biggest challenge in semisolid processing of high-performance aluminum alloys is the narrow temperature processing windows of these alloys, and as a result, the preparation of qualified semisolid slurries is very important. High solid fraction slurries of high-strength A201 alloy were prepared by the Swirled Enthalpy Equilibration Device (SEED) process. The cooling behavior and microstructures of the A201 slurries produced by the standard, as well as a modified, SEED process were investigated. The results show that qualified A201 slurry can be produced by decreasing the pouring temperature and controlling the processing time in the SEED process. The modified SEED process significantly reduced the radial temperature gradient of the melt, due to the slow cooling rates involved, with the resulting slurries being more uniform, with more spherical microstructures, as compared to those produced by the standard SEED process. The formation of the nondendritic grain structure in the SEED process is attributed to the uniformly distributed large number of nuclei within the melt and the slow cooling of the melt in the containing crucible. [ABSTRACT FROM AUTHOR]