Swirled Enthalpy Equilibration Device Research Articles

Microstructure, segregation and mechanical properties of A356 alloy components fabricated by rheo-HPDC combined with the swirled enthalpy equilibration device (SEED) process

The challenges commonly associated with conventional high pressure die casting (HPDC) have led to increased interest in semi-solid metal (SSM) forming processes. In the present study, semi-solid slurries of A356 alloy prepared by the Swirled Enthalpy Equilibration Device (SEED) process were used for manufacturing components with complex shape by using a high pressure die casting machine. The segregation phenomenon and the effect of heat treatment on the microstructure evolution and mechanical properties were investigated. The results showed that the alloy consists of primary spherical α-Al grains, secondary solidified α-Al grains, eutectic Si, iron-rich intermetallic phases and low porosities. The microstructural investigations revealed that the eutectic Si particles underwent fragmentation, spheroidization and coarsening with increasing solution temperature. Furthermore, the solution treatment results in the dissolution of the π-Al8FeMg3Si6 phase and the growth of the β-Al5FeSi phase. The hardening peaks at 170 °C could be obtained with ageing for 5 h. Due to both solution and precipitation strengthenings, the yield strength, ultimate tensile strength and hardness of A356 alloy after heat treatment increase significantly compared to those in the as-rheocast state: they reach 266 MPa, 343 MPa and 110 HV0.2, respectively. The analysis of fracture surfaces of rheo-HPDC samples in both the as-rheocast and the heat-treated states revealed a mixed mechanism of dimples and quasi-cleavage. The microstructure inside the part was found to be quasi-homogeneous while the segregation phenomenon in different zones of the part is affected by die geometry during the filling process. The results imply that the SEED-HPDC process has the potential to be industrialized by implementing appropriate heat treatments for producing complex components with good mechanical properties.

Rheological Modeling of 7075 Aluminum Alloy Semi-Solid Slurry and its Application in the Simulation of SEED Rheocasting Process

Rheocasting technology has been successfully applied to produce aluminum alloy parts of automobile and communication equipment. However, its application scope is still limited. One reason is that the strength of the applied alloys is limited. In recent years, lots of researchers have tried to use 7075 aluminum alloy in the rheocasting process because this alloy has excellent mechanical properties. In this work, the rheological behavior of 7075 aluminum alloy semi-solid slurry is studied through shear stress-controlled test and shear rate-controlled test. Then the constitutive parameters in Power-Law (PL) model or Carreau-Yasuda (CY) model of non-Newtonian fluid are determined. The models are used to simulate the flow behavior of 7075 aluminum alloy semi-solid slurry in Swirled Enthalpy Equilibration Device (SEED) rheocasting process. The simulation results indicate that the CY model derived from the shear rate sweep test is more suitable for simulating the flow behavior of 7075 aluminum alloy semi-solid slurry during rheocasting than the other models.

Progress of Semi-Solid Processing of Alloys and Composites in China

Following the rapid growth of the automotive and communication industries, components with high quality and low cost are eagerly desired in China. Various technologies have been developed in China to meet the demand, while semi-solid processing (SSP) of alloys and composites is one of the most successfully developed and practically applied technologies. The major SSP applied in China is the rheocasting in terms of the Swirled Enthalpy Equilibration Device (SEED) process. In this review, we start with a brief reviewing some common slurry preparation methods and recent innovations of the SEED process. Subsequently, we describe the general situation and some recent examples of successful development and applications of SSP in China. Lastly, the future directions in SSP of alloys and composites are highlighted in this frontier research field at the end of this review.

Cooling Behavior and Microstructure of Semisolid A201 Aluminum Alloy Prepared by the SEED Process

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.

Mold-Slug Interfacial Heat Transfer Characteristics of Different Coating Thicknesses: Effects on Slug Temperature and Microstructure in Swirled Enthalpy Equilibration Device Process.

Application of a coating on a mold surface is widely used in the foundry industry. Changes in coating change the heat transfer at the mold–melt interface, which influences the microstructure of the casting. In this study, the effect of boron nitride coating thickness on the interfacial heat transfer and slug microstructure in the Swirled Enthalpy Equilibration Device (SEED) process was investigated. The temperatures of the semi-solid slug and mold were measured, and the interfacial heat transfer coefficient and heat flux of the mold–slug interface was estimated based on these data. Microstructures of the quenched slugs were also examined. The results indicated that the interfacial heat transfer coefficient decreased with an increase in coating thickness and was sensitive to a coating thickness of less than 0.1 mm. The interfacial heat flux decreased sharply at the early stage, and then slowed down as the swirling time increased and the coating thickened. The coating thickness affected the temperature evolution of the slug at the early stage of the SEED process. As the coating thickness increased from near zero to 1.0 mm, the grain size of the slug increased by ~20 µm and the globular structure of the slug transformed into a dendritic structure.

Model for Predicting Radial Temperature Distribution of Semi-Solid Slug Produced by Swirled Enthalpy Equilibration Device (SEED) Process

The temperature distribution of a semi-solid slug, which determines its fraction solid distribution, is a key parameter for semi-solid die casting. No literature is, however, available regarding temperature control for a semi-solid slug produced by the Swirled Enthalpy Equilibration Device (SEED) process. This work focused on revealing the relationship between the radial temperature difference in the slug and parameters of the SEED process. A model that includes seven parameters was established to illustrate the relationship by theoretical analysis. The model was verified by finite element simulation and experimental data. Results showed that the heat-transfer coefficient of the crucible-air interface and the slug radius are the key parameters for reducing the radial temperature difference of the slug. Methods for producing a large mass of slug using an alloy with a narrow freezing range (between 35%–55% solid fraction) are discussed.

Effect of T6 Heat Treatment on the Microstructure and Hardness of Secondary AlSi9Cu3(Fe) Alloys Produced by Semi-Solid SEED Process

The effect of the T6 heat treatment on the microstructure and hardness of a secondary semi-solid AlSi9Cu3(Fe) alloy have been investigated by using optical, scanning and transmission electron microscopy and hardness testing. The semi-solid alloy was produced using the swirled enthalpy equilibration device (SEED). The solution heat treatments were performed at 450, 470 and 490 °C for 1 to 6 h followed by water quenching and artificial ageing at 160, 180 and 220 °C for holding times ranging from 1 to 30 h. The microstructural investigations have revealed the spheroidization of the eutectic Si and the dissolution of the majority of Cu-rich compounds after all the solution heat treatments; moreover, the greater the solution temperature and time, the higher the hardness of the alloy. Unacceptable surface blistering has been observed for severe solution condition, 490 °C for 3 and 6 h. The artificial ageing at 160 °C for 24 h has led to the highest alloy strengthening thanks to the precipitation of β” and Q’ (or L) phases within the α-Al matrix. The hardening peaks at higher temperatures have been early achieved due to faster hardening kinetic; however, the lower number density of β” and Q’ (or L) phases and the presence of coarser θ’ precipitates result in a reduction of hardness values for peak aged condition at 180 and 220 °C, respectively.

Microstructural and mechanical features of aluminium semi-solid alloys made by rheocasting technique

The rheocasting process applied by Swirled Enthalpy Equilibration Device (SEED) technique relies on rapid extraction of a controlled quantity of heat from the liquid aluminium alloy via mechanical agitation to form the semi-solid slurry that can be formed under pressure. Microstructural characteristics of both conventional and semi-solid A357 castings under T6 heat treatment conditions were examined using optical and scanning electron microscopy. The fatigue and tensile experiments were applied to evaluate the effect of SEED technique on the mechanical properties of T6-A357 semi-solid alloys and conventional castings. The results showed that the rheocasting–SEED technique has proved successful in producing optimum microstructure of Al–Si–Mg semi-solid alloys providing an excellent combination of quality and mechanical performance as compared to conventional technique.This paper is part of a Themed Issue on Aluminium-based materials: processing, microstructure, properties, and recycling.

Materials Performance and Design Analysis of Suspension Lower-Arm Fabricated from Al-Si-Mg Castings

The diversity of physical and mechanical properties of aluminum alloys leads to develop a variety of manufacturing processes including the semi-solid casting process. Fatigue failure is considered the most common problem occurred in automotive engineering applications by which the vehicle components, mainly suspension system parts, fail under conditions of dynamic loading. It is well known that the fatigue life of aluminum castings, mainly A357, is very sensitive to casting design as well as to casting defects and microstructure constituents. The fatigue characteristics of automotive lower suspension arm made of semi-solid A357 aluminum castings have been investigated using metallurgical and analytical approaches. The critical stress areas capable of initiating cracks during fatigue tests are detected by using fatigue experimental design for real part materials by the installation of strain gages on the suspension arm to calculate maximum stress; further more, analytical approach is applied using modelling software. Microstructure characteristics of the semisolid A357 under T6 heat treatment conditions are examined using scanning electron microscope. The results show that using the SEED casting technology (Swirled Enthalpy Equilibration Device) has an efficient effect on the mechanical and metallurgical characteristics of real part materials that are also affected by castings design.

Comparison of Microstructure and Mechanical Properties of Semi-Solid Castings Produced Using Billets Made by EMS and SEED

The spheroidal grains in billets used for semi-solid casting are generally manufactured by electromagnetic stirring (EMS) during the casting process. This method however, is not economically applicable for small quantities of the thixo billets. Swirled Enthalpy Equilibration Device (SEED) has been developed as a rheocasting process, and the SEED process is of interest for developing new thixo alloys, as well as for optimizing the thixocasting processes for high quality components. The objective of this paper is to compare the microstructure and mechanical properties of aluminum alloy 319s billets and castings produced using EMS and SEED feed materials. The experimental results show that for as-cast billets made from SEED process, a well-developed spheroidal grain structure is distributed throughout the cross-section of the billet, while for as-cast EMS billets, the grain structure is inhomogeneous, i.e., a dendritic structure was present adjacent to the surface of the billet, while a uniform, spheroidal structure was present at the centre. After the thixocasting process, however, the both SEED and EMS billets have well-developed, spheroidal grain structures. Mechanical properties of thixocast and T61 heat treated components are comparable for the both SEED and EMS billets.

On the Rheocasting of High Integrity Hollow Shape Components for Automotive Applications Using 357 Aluminum Alloy

Recent studies regarding semi-solid casting as a viable alternative to conventional liquid metal casting have been met with considerable interest. The dual nature of semi-solid materials results in a marked decrease in internal defects otherwise associated with conventional casting methods. In recent years, the National Research Council Canada - Aluminum Technology Centre (NRC-ATC) has dedicated itself to better understanding the behaviour of semi-solid aluminum alloys, notably 357, using the SEED (Swirled Enthalpy Equilibration Device) rheocasting method. SEED is a novel process which relies on the mechanical agitation and cooling of molten aluminum to produce a semi-solid billet. This billet is then injected into a die to yield the desired cast shape. The current work focuses on the rheocasting of a 357 aluminum alloy support bracket, consisting of four rings. Material flow around a ring is known to result in a welding of the two metal fronts. Traces of porosity and oxides can sometimes be found at the weld, unless preventative measures are taken. These include the use of overflows attached to the ring via a web as well as a careful control of the casting parameters. At NRC-ATC, several parts were rheocast and then subjected to both destructive and non-destructive testing, in an effort to better understand the material flow behaviour around these rings. The results obtained are presented herein.

Effect of Heat Treatment on the Mechanical Properties of a Rheocast 357 Alloy Using the SEED Method

The ability of Al-Si alloys to be cast into complex shapes, coupled with a favourable strength-to-weight ratio, has given them an advantage in the automotive industry. To further improve casting quality, many have turned to semi-solids, where alloys exhibit flow properties that stem from the material's dual liquid-solid nature and globular microstructure. The SEED (Swirled Enthalpy Equilibration Device) process is a novel rheocasting technology yielding a semi-solid slurry from the mechanical agitation (swirling) and cooling of molten aluminum. In the current work, a SEED processed 357-T6 alloy displayed typical yield and ultimate tensile strength values of 210-250 and 300-320 MPa, respectively. Furthermore, the average elongation observed was 12-17%.

Rheological behavior of semi-solid Al–Si alloys: Effect of morphology

Swirled enthalpy equilibration device (SEED) technology was used to cast semi-solid metal, SSM, billets of A356 Al–Si alloy. The deformation behavior of the SSM billets was studied using parallel plate compression viscometry. The compression tests were carried out at different applied pressures and solid phase morphologies. The rheological studies were conducted assuming the SSM slurry behaving like Newtonian or non-Newtonian fluid. The calculated viscosity numbers confirmed psuedoplastic behavior of the SSM billets and were correlated to the morphology, average aspect ratio, and shear rate to highlight the effect of metallurgical and process parameters on the viscosity and thus “rheological behavior” of SSM alloys. An empirical equation is proposed to correlate viscosity with average aspect ratio and shear rate: log η = − 1.85 + 4.9 AR ¯ − ( 0.255 AR ¯ + 0.03 ) log γ ∘ , 1.4 < AR ¯ < 1.8 This equation is valid for the shear rates less than 0.01 s −1.

Effects of modification during conventional and semi-solid metal processing of A356 Al-Si alloy

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.