Rheocasting Process Research Articles

New Addressable Applications for Rheocasting to Escape from an Oversupplied Market

The current market change of aluminium HPDC castings started with the “Dieselgate”. First, there was a shift from diesel to petrol engines. In the second step, hybrid and battery-powered cars gained significant market shares in sales statistics. Therefore, lucrative powertrain components are falling away. As powertrain foundries still want to utilize their machines to capacity, they are pushing into the structural castings market. As a result, there is an oversupply of casting machines here, which massively depresses prices and, thus, margins for tenders. With rising energy costs, these declining margins were eaten up, bringing foundries into crisis. Implementing Rheocasting at the existing die-casting cells is the solution to move into new market shares that are now not accessible in conventional HPDC.One of the new applications is electronic housings, high wall thickness parts, and fatigue bearing parts. These parts are commonly manufactured in sand or gravity castings because of their high wall thickness and low tolerance of porosity. Rheocasting is the perfect process for high-wall thickness components. Because of the semisolid melt preparation and the lamellar filling behavior, these components can be manufactured from the same alloy without pores or voids.This flow behavior of the semisolid slurry also results in a longer flow length. Slower casting speeds and lower pressure settings result in lower clamping forces. This gives an advantage in production costs and targets battery constructions made of castings and sheet metal. Structural battery housings must be leak-tight, even in a crash event. Having it in one casting instead of an assembly reduces the leakage area and improves crash performance.Another industry that relies on Rheocasting is the telecommunications industry. The power electronics in these 5G modules are significantly larger and generate much more waste heat. Until now, many antennas have been actively cooled or milled from a block of aluminum. The milled housings are significantly too expensive to enable series production. Therefore, the goal is to reproduce the passively cooled modules in die casting. Due to the process, the thermal conductivity in conventional HPDC is around 120 to 130 W/m*K. Similarly, no slim cooling fins can be formed. Only the Rheocasting process makes it possible to cast other alloys with low proportions of alloying elements, such as AlSi2Mn. This allows fins with a wall thickness of down to 0.4 mm and thermal conductivity of up to 190 W/m*K.Rheocasting enables access to market segments out of reach. These bring an unbeatable cost advantage against the current suppliers: gravity and sand casters. The low cycle time in Rheocasting brings back the high margins needed to sustain the business. Also, these products can be delivered with even better properties on smaller casting machines.

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.

Nghiên cứu sự thay đổi tổ chức tế vi của hợp kim nhôm ADC12 trong quá trình đúc lưu biến

In this study, pouring temperature and cooling rate are two processingparameters that directly affect the microstructurechange of ADC12 aluminium alloy. The research results show that the ADC12 aluminium alloy microstructureduring the rheocasting process changes from dendritic to spherical microstructurewith α-Al particle fraction of over 80%. The cooling rate is the main parameter that directly affects the formation of the spherical microstructureof α-Al particles. Pouring temperature affects the size and sphericity of α-Al particles. The research results can be applied to change the microstructureof aluminium alloy ADC12 to help the alloy increase the ultimate strengthand elongation, but still maintain other mechanical properties. In other words, increasing the reliability of the part formed by the rheocasting method.

The Effect of Solution Time on the Microstructure of A356.2 Aluminum Alloy Provided by Rheocasting and Squeeze Casting

The evolution of the microstructure of A356.2 alloys prepared by the rheocasting and squeeze casting during solution heat treatment was investigated. In contrast with the conventional solution heat treatment process (3 hours at 540oC), a short time solution treatment process (less than 1 hour at 540oC) is applied in this paper. The results show that the rheocastings require a shorter solution time than the squeeze-castings to obtain spheroidized Si particles. After solution for 10 min, the X-ray diffraction inspection results show that the Mg2Si phase completely is dissolved in both rheocastings and squeeze-castings. However, a small amount of Mg2Si is found at the edge of the Si particle by scanning electron microscope observation. After solution for more than 20 min, the Mg2Si phase is completely dissolved. Fe-rich phases, including AlSiFeMg and AlFeSi, exist throughout the solution process. The developed T6 heat treatment with a short solution time can effectively improve production efficiency and decrease process cost for the rheocasting process. Key words: A356.2 alloy, microstructure, short solution time, rheocasting, squeeze casting

Influence of Fe-rich intermetallics and their segregation on anodising properties of Al-Si-Mg rheocast alloys

During rheocasting of Al alloys, the component's surface can be enriched in Fe-rich intermetallics due to the surface liquid segregation or the interaction with the die material. Although this precipitates enrichment affects only the surface, it can have a big impact on the quality of the surface treatments or durability. In this paper, the effect of Fe-rich intermetallics on the hardness and corrosion resistance of the anodized layer of AlSiMg alloys was examined by using nanoindentation and electrochemical impedance spectroscopy (EIS) techniques. A sulfuric acid anodising process was performed on unground and mechanical ground surfaces of TX630 substrates produced by the rheocasting process. During anodising, Fe-rich intermetallics can be dissolved, leaving voids in the oxide during its growth. The anodised samples with two different oxide layer thickness (4 and 7 μm) were tested by EIS in 3 wt-% NaCl solution for 12 h. A comparison of the EIS results of unground and mechanically ground surfaces demonstrated that the mechanical grinding successfully removed the Fe enriched layer, improving corrosion protection of the anodised oxide. Moreover, the hardness measurements indicate that the oxide layer on the mechanically ground surface with low Fe content shows higher hardness than on the unground surface with high Fe content. • Rheocasting surface can be enriched in Fe-rich intermetallic in form of Fe-rich skin. • Fe-rich intermetallic under the oxide layer facilitate the corrosion of the matrix. • The removal of Fe-rich skin makes the oxide layer harder and more resistant to corrosion.

Failure Analysis of Rheocast Cylinder Head Covers of Hypereutectic Al\u2013Si Alloys

The purpose of the present study is to determine the cause of failures of semisolid rheocast cylinder head covers of hypereutectic modified LM30 alloys. The covers, manufactured by rheocasting, a process that consists of the incorporation and homogeneous distribution of the reinforcements in semisolid metal (SSM) before die casting, were shot-peened after heat treatment to increase the fatigue resistance. However, these engine components failed during operation after a short service time. The major flaws were located by radiography. The microstructure was controlled by metallography. Significant interactions between shot peening and surface/subsurface contaminants were identified by surface morphology and fractography. The fatigue properties of hypereutectic alloys were investigated by a high-frequency vibrophore. It was identified that the failure was related to the cleanliness of SSM as well as the rheocasting process. Recommendations were given to prevent the recurrence of similar failures.

Microstructure Evolution of a Semisolid Magnesium Alloy Slurry Obtained via an Internal Rapid Cooling Stirring Process (IRCSP)

Grain refinement of magnesium alloys is an effective way to improve their tensile strength and ductility to meet industrial application requirements. Herein, a new rheocasting process, internal rapid cooling stirring process (IRCSP), was used to obtain a fully grain-refined spherical semi-solid slurry. Rapid quenching was used to study the microstructure evolution during IRCSP. The experimental results showed that the solid fraction was mainly determined by nucleation, and grain growth played only a minor role. The particle density was determined by a combination of the fragmentation and coalescence of solid particles. Changes in grain size over time followed a 1/3 power law with a ripening coefficient. In addition, the particle distribution was determined using shear stress flow and cooling rates. The microstructural analysis suggested that a fast cooling rate led to grain refinement, and rapid stirring enhanced the interfacial energy and stability of the solid-liquid interface. As a result, fine globular primary α-Mg particles were obtained during IRCSP.

Simulation and Experimental Study on the Steady Conduction Solution for Continuous Rheo-Casting for A356 Alloy

Computational fluid dynamic modeling of a continuous rheo-casting technology was conducted, consistent with the manufacturing of 3 mm-thin plates made of aluminum alloy A356. The A numerical simulation on of the stabilizing time of the material crystallization was carried out using the ANSYS FLUENT code. Solidification and melting models were simulated with heat transfer and solid-liquid phase transformation involving the latent heat of crystallization were simulated. The calculated temperature distribution and the evolution of cooling rate through the material were examined and used to clarify their influence on microstructure, and further investigated with hardness testing. The thickness of the mushy zone was determined for the steady conduction solution of the continuous rheo-casting process. (Received December 29, 2015; Accepted August 9, 2016)

Microstructural evolution and mechanical properties of rheocast Al-7.1WT%Si alloy

Effects of Semi-Solid Rheocasting (SSR) process on the structure and mechanical properties of Al-7.1wt%Si alloy were studied. The results showed that the non-dendritic structure could be formed by a short stirring period below liquidus temperature provided that stirring was combined with localized rapid heat extraction from the melt. The effect was examined by calculation of the time needed for detachment of dendrite arms at the initial stages of solidification and was associated with a large particle density in the rheocast slurry. Samples processed in semisolid state had lower porosity, higher tensile strength and higher elongation than that processed in fully-liquid state. The SSR- processed sample had a lower tensile strength but a higher elongation than the sample cooled without localized cooling and stirring. It was suggested that the lower strength of SSR-processed alloy was related to the inability of the α-particles to restrain crack propagation through the brittle eutectic matrix.

Investigation on Liquid Segregation during Rheo-Casting Process Based on Eulerian-Granular Multiphase Model

A crucial problem concerned with the semi-solid forming process is the liquid segregation phenomena during shape formation, especially for rheo-casting process. Liquid segregation occurs due to the separation phenomena of the solid grain and the liquid phase. In this work, using commercial finite element software, the liquid segregation during rheo-casting process was numerically investigated by Eulerian-granular multiphase model based on the comparable results of single phase model, Eulerian-granular two-phase and three-phase model, along with Eulerian-granular DDPM three-phase model. In the study, solid grains and liquid phases were regarded as rigid material and non-Newtonian fluid at microscale, separately. This validation was experimentally proved and also compared to the proposed relationship of power law, Herschel-Bulkley model with yield stress at macroscale.

Microstructure and Properties of LPSO Phase Reinforced Mg Alloy Produced by Rheocasting

The long period stacking ordered (LPSO) phase reinforced Mg alloys have received many researches in recent years because of their excellent mechanical properties. However, the LPSO phase usually concentrates at the grain boundaries with a coarse network structure, which seriously deteriorates its strengthening effect. In this research, rheocasting and ultrasonic vibration (USV) process were firstly used to refine the LPSO phase in Mg alloy. The semisolid slurry of Mg96.9Y2Zn1Zr0.1 (at.%) alloy was prepared by USV and then formed by rheo-squeeze casting (RSC). The effects of USV and squeeze pressure on the microstructure and mechanical properties of this Mg alloy were investigated. The results show that the primary α-Mg and coarse LPSO phases were refined obviously by USV and RSC. The tensile strength and elongation of the RSC Mg96.9Y2Zn1Zr0.1 alloy were 232 MPa and 17.7% respectively, which were increased by 17.8% and 172.3% respectively compared to the conventional liquid casting alloy. The refinement mechanism of the LPSO phase in semisolid Mg alloy is also discussed.

Development and Achievements of SSM Processes for High Performance Components

During the last decades under the enthusiastic and competent guidance of Mr Chiarmetta SSM processes attained in Italy at Stampal Spa (Torino) an unquestionable high level of industrial development with the production of large numbers of high performance automotive parts, like variety of suspension support, engine suspension mounts, steering knuckle, front suspension wheel, arm and rear axle. Among the most highlighted findings SSM processes demonstrated their capability to reduce the existing gap between casting and forging, moreover during such a processes there are the opportunity to better control the defect level.Purpose of this paper is to highlight the research work and the SSM industrial production attained and developed by Mr G.L. Chiarmetta, as well as to give an overview concerning some alternative methods for the production of enhanced performance light alloys components for critical industrial applications and to present an analysis of a new rheocasting process suitable for the manufacturing of high performance industrial components.

Microstructure and Rheological Properties of Semi-Solid 7075 Slurries Using SEED Rheocasting Process

The SEED rheocasting process was used to produce semisolid slurries of high strength 7075 aluminum wrought alloys. The effects of the SEED processing parameters on the microstructure of semisolid slurries were studied. The impact of grain refinement on the grain morphology and size was investigated. The rheological properties of semisolid 7075 alloys were characterized at different solid fractions using a parallel plate compression viscometer. Results indicated that the grain refinement could greatly improve the globularity of α-Al grains and rheoformability. The relationships between viscosity and shear rate at different solid fractions in the transient state for both unrefined and refined semisolid slurries were evaluated and discussed.

Study on Rheo-Continuous Casting of Al-Si A356 (EN AC4200) Alloys

Rheo-continuous casting method is a combination of rheo- and continuous castings. In rheo-casting process the nucleation occurs on cooling slope with high rate in whole casting volume, so nuclei are numerous, resulting in very fine microstructure of nodular crystals. In this work the rheo-continuous process was carried out with a casting machine using 2 rollers of same size: diameter of 300 mm and width of 100 mm. The pouring temperature is near-liquidus. The microstructure obtained is fine (grain size < 40 μm), with nodular morphology. The mechanical properties of as-cast samples were high (the tensile strength is above 220 MPa).

Die design method for thin plates by indirect rheo-casting process and effect of die cavity friction and punch speed on microstructures and mechanical properties

Thin plates with a thickness of 1.2mm are fabricated from semi-solid A356 alloy through an indirect rheo-casting process both with and without an electromagnetic stirrer (EMS). The thin die cavity for forming is designed with the fluid analysis software MAGMA. A semi-solid slurry with a solid fraction of 40% is prepared and then injected into the die of a 200t hydraulic press. Forming tests are performed on the thin plates at two punch speeds (30 and 300mm/s) and two cavity friction conditions (mf=0.4 and mf=0.9). The formability, mechanical properties, and microstructure are then evaluated. The semi-solid slurry obtained with an EMS contains fine and globular solid particles; the semi-solid slurry produced without an EMS reveals rosette particles and coarser globular solid particles. At high friction (mf=0.9), the cavity is mainly filled with the liquid phase. At a higher punch rate, the thin plates show better formability and a microstructure with fine and even solid particles. The tensile strength and elongation of the thin plate formed with a punch speed of 300mm/s in the cavity with graphite lubrication (mf=0.9) are 216MPa and 10%, respectively. These values are 57MPa and 5.5% higher, respectively, than those of the thin plate formed at a punch speed of 30mm/s.

Microstructural evolution of A380 aluminum alloy produced by gas-induced semi-solid technique (GISS)

Gas-induced semi-solid (GISS) technique is a new rheo-casting process that utilises the principle of rapid heat extraction and vigorous local convection using the injection of fine gas bubbles through a graphite diffuser in molten metal. This study presents microstructural evolution of A380 aluminium alloy produced by GISS process. Samples of semi-solid A380 aluminium alloy were taken at different gas injection times in an optimum temperature above liquidus. Microstructural studies revealed that after conducting GISS process, the morphology of primary α-Al changes from coarse dendritic to rosette-like and finally to fine globular. The sphericity of 0.88, particle size of 54.23 μm and number of 177 α-Al particles per mm2 for α-Al phase were achieved using GISS technique under optimum condition. The results showed the well distribution of α-Al phases in the microstructure of the alloy produced by GISS process. Also the impact strength of A380 alloy was increased with employing GISS process, and more ductility of A380 alloy was achieved.

Microstructural characteristics and mechanical properties of Al-2024 alloy processed via a rheocasting route

This article reports the effects of stirring speed and T6 heat treatment on the microstructure and mechanical properties of Al-2024 alloy synthesized by a rheocasting process. There was a decrease in grain size of α-Al particles corresponding to an increase in stirring speed. By increasing the stirring speed, however, the globularity of matrix particles first increased and then declined. It was also found that the hardness, compressive strength, and compressive strain increased with the increase of stirring speed. Microstructural studies revealed the presence of nonsoluble Al15(CuFeMn)3Si2 phase in the vicinity of CuAl2 in the rheocast samples. The required time for the solution treatment stage was also influenced by stirring speed; the solution treatment time decreased with the increase in stirring speed. Furthermore, the rheocast samples required a longer homogenization period compared to conventionally wrought alloys. Improvements in hardness and compressive properties were observed after T6 heat treatment.

Microstructure Evolution and Mechanical Properties of Rheocast A319 Aluminum Alloy Using Cooling Slope

A319 aluminum alloys are commonly used in automotive industry due to a combination of good fluidity and mechanical strength. In this present work, cooling slope (CS) rheocasting process was employed to produce A319 billets with near spherical morphology of primary Al phase. The dendritic primary phase in the cast A319 alloy had readily transformed into non-dendritic when the ingots were cast over a cooling plate from pouring temperatures between 620°C and 640°C and with cooling lengths of between 300 mm and 400 mm. The shear driven flow of the solidifying melt on the cooling slope wall promotes heterogeneous nucleation of α-Al phase and subsequent separation from there due to shear driven flow of the solidifying melt produced nearly spheroidal morphology of the primary phase in the microstructure. The results show that the best combination of pouring temperature and cooling length was found to be 630°C and 400 mm respectively. The hardness of the rheocast ingots improved to 85.3 HV from 81.8 HV in as-cast condition.

Microstructure and Properties of In Situ Si and Fe-rich Particles Reinforced Al Matrix Composites Assisted with Ultrasonic Vibration

In this research, the in situ Si and Fe-rich particles reinforced Al matrix composites were fabricated by rheocasting (RC) process assisted with ultrasonic vibration (USV). After USV treatment, the polygonal primary Si crystals were refined into particles with average diameter of about 15–23 μm, and the fraction of primary Si declined to about 5.4–6.5 vol%. The coarse plate-like δ-Al4(Fe,Mn)Si2 phase was transformed into fine particles with average diameter of about 17–20 μm, and the fraction of particle-like Fe-bearing particles is about 3.6–5.3 vol%. The ultimate tensile strength of the RC composites increases with the increase of Fe content at 350 °C. The increase of the elevated temperature strength of the composites is mainly attributed to the refinement of δ-Al4(Fe,Mn)Si2 phase and the increase of the volume fraction of the Fe-bearing compounds. Compared with the composites without USV, the RC composites assisted with USV have thinner mechanical mixing layer in wear test, which corresponds to smaller wear rate.

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.