Semi-Solid Rheocasting Research Articles

Enhanced combination of strength and ductility in the semi-solid rheocast hypereutectic Al[sbnd]Si alloy with the effect of in-situ TiB2 particles

This study aims to address the issues of low strength and high brittleness associated with common industrial hypereutectic aluminum alloys. We report here that the addition of TiB2 particles (TiB2p) not only enhances the strength of the rheocast hypereutectic Al17Si alloy, but also exerts a positive effect on its ductility. As the content of TiB2p reaches 6 wt%, the strength and ductility of composites are increased by 63.4% and 62%, respectively (UTS = 283.3 MPa, and EL = 1.62% in this study). The EBSD results show that the densities of low-angle and high-angle grain boundaries increase with the content of TiB2p. The interfaces of TiB2p/Si and TiB2p/Al are investigated by TEM, HRTEM, and an atomic structure model simulation. A model addressing dislocation multiplication, and crack initiation and propagation is developed to elaborate the strength-ductility synergy mechanisms of the TiB2p/Al-17Si composite.

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.

Optimization of Pouring Temperatures and Stirrer Speed Parameters on a Semi-Solid Slurry of ADC12 Al Alloy Prepared by Mechanical Stirring

This paper presents an experimental design approach for the optimization process parameters for the aluminum solid alloy casting of ADC12 alloys. To achieve this goal, the pouring temperatures and stirring speed are selected and two levels of this parameter are considered. Design of expert (DOE) of tests was used for experimental design and analysis of results. The aluminum ADC12 slurry is stirred by a mechanical stirrer (round rods stirrer models) with a variation of speed 250, 300, 350 rpm for 20 seconds. Furthermore, the aluminum slurry of ADC12 is poured on a metal mold with a temperature of 620 °C, 600 °C, and 580 °C. The microstructure characteristics were examined by direct observation using optical microscopy, secondary α-Al phase dendrite arm spacing and shape factor were identified. The mechanical properties were investigated by the hardness test and tensile test. The mechanical properties and microstructure of aluminum alloys ADC12 made with semi-solid rheocasting casting technology using several parameters pouring temperature and stirring speed have been studied, and the results obtained can be synergized as follows. ADC12 aluminum alloy slurry preparation using a round rod mechanical stirrer on semi-solid casting can improve mechanical properties. Low pouring temperature and high stirring speed are reliable techniques for producing the right mechanical and microstructure properties for a semi-solid casting process (Rheo casting). The pouring temperature and stirring speed are recommended to produce optimal mechanical properties and the round microstructure is 580 °C and 350 rpm.

Kesan Proses Pembentukan Tuangan Reo terhadap Sifat Mikrostruktur dan Mekanikal Aloi Al-5.7Si-2Cu-0.3Mg

This study shows the results of an experimental investigation of semisolid rheocasting of Al-5.7Si-2Cu-0.3Mg alloy using a cooling slope (CS) casting technique. However, the challenge is to determine process parameters of the CS process to get a desirable microstructure in the semisolid feedstock material. cooling slope technique was employed to create feedstock material for thixoforming under an argon gas atmosphere, where on an inclined plate that was fixed at a 60° slope angle, molten alloy is poured at different temperatures of 640°C, 650°C and 660°C at lengths 300, 400 and 500 mm. Examination the microstructure with optical microscope observed that the microstructure of conventionally cast alloy presented coarse and dendritic primary α-Al phase, whereas rheocast alloy included fine and nondendritic primary α-Al phase with homogeneous distribution of eutectic phase. The best CS processing condition has been identified for optimum pouring temperature of 650°C and the slope length of 400 mm as average globular grain size of around 31.67 ± 3 μm and a shape factor of about 0.66 ± 0.09 were obtained. The mechanical properties of conventional cast alloy were enhanced by the CS casting process. The ultimate tensile strength, the yield strength and elongation of the rheocast alloy were increased by 10%, 12% and 22% respectively compared to the conventional cast alloy. due to a reduction in shrinkage and porosity of the microstructure of the CS alloy.

Optimization of stirring parameters on the rheocast microstructure and mechanical properties of aluminum alloy ADC12

This paper presents an experimental design approach for the optimization process parameters for the aluminum solid alloy casting of ADC12 alloys. To achieve this goal, the stirring time parameter and stirring speed are selected and two levels of this parameter are considered. Design of expert (DOE) of tests was used for experimental design and analysis of results. The aluminum ADC12 slurry is stirred by a mechanical stirrer (straight plate stirrer models) at 610°C with a variation of speed 250, 300, 350 rpm for 20, 40, 60 seconds. Furthermore, the aluminum slurry of ADC12 is poured on a metal mold with temperature 600°C. The microstructure characteristics were examined by direct observation using optical microscopy, secondary α-Al phase dendrite arm spacing and shape factor were identified. The mechanical properties were investigated by the hardness test and tensile test. The microstructure and mechanical properties of aluminum alloys ADC12 made with semi-solid rheocasting casting technology using several parameters stirring have been studied, and the results obtained can be synergized as follows. The highest mechanical properties (Hardness 122,5 HB, Tensile strength 238.2 N / mm2) occur at 300 rpm stirring speed and 20 seconds stirring time. Secondary Dendrite Arm Spacing (SDAS) lowest occurred at 25 rpm stirring speed and 20 seconds stirring time of 13.93 μm. The highest shape factor occurs at 300 rpm stirrer spin and 20 seconds stirring time of 0.47. The optimal stirring parameters recommended for producing a hardness response of 122,071 HRC, tensile strength 236,271 N / mm2, Shape Factor (SF) 0.38994, and Secondary Dendrite Arm Spacing (SDAS) are 317 rpm (stirring speed) and 20 seconds (stirring time).

Microstructural Development of Aluminum A201 Alloy Semi-Solid Processing Feedstock Produced by Different Routes

Thixoforming or Semi-Solid Metal (SSM) forming is a manufacturing route that relies on a non-dendritic microstructure, a structure that is retained after processing resulting in components of fine and uniform microstructures with enhanced mechanical properties as compared to conventional cast products. In this project, an investigation is conducted on the microstructural development of Aluminium A201 alloy in the semi-solid range, through a combination of variable time and temperature conditions. Using equilibrium and non-equilibrium (Scheil) curves, the solidus and the liquidus temperatures as well as the melting behaviour of this alloy are estimated. The temperature range for the thixoforming process typically lies within the 40-60% fraction liquid and this is found to be between 620oC to 637oC for this particular alloy. The aim is to heat treat specimens of this alloy within the semi-solid range (the process window) and observe the resulting microstructures to establish if they comprise of near-spheroidal solid phase particles surrounded by a liquid phase. This microstructure gives the material its thixotropic properties; i.e. the material flows like a liquid when sheared but thickens and behaves like a solid when it is allowed to stand. Three different routes for obtaining the non-dendritic microstructure necessary for thixoforming are investigated in this work: Magneto-Hydrodynamic (MHD) stirring, Strain Induced Melt Activated (SIMA) and Semi-Solid Rheocasting via Cooling Slope (SSR+CS) route. These routes are compared and their potential for future thixoforming applications studied.

Effects of stirring parameters on the rheocast microstructure and mechanical properties of aluminum alloy ADC12

In this study, effects of stirring time and stirring speed on the microstructure of semisolid rheocast (SSR) aluminum alloy ADC12 were examined. The research method was done by gravity casting using a metal mold. The aluminum ADC12 slurry is stirred by a mechanical stirrer (round rod stirrer) at 610OC with a variation of speed 0, 250, 300, 350 rpm for 0, 20, 40, 60 seconds. Furthermore, the aluminum slurry of ADC12 is poured on a metal mold with temperature 600OC. The microstructure characteristics were examined by direct observation using optical microscopy, secondary -Al phase dendrite arm spacing, shape factor, and Si eutectic phase were identified. The mechanical properties were investigated by hardness test and tensile test. A short period of stirring below the liquidus temperature to form a non-dendritic structure. The final morphology of the primary particles after a short period of stirring time has little impact as the stirring time increases. The optimal mechanical properties (hardness and tensile strength) were obtained at 20 seconds of stirring time and 300 rpm of stirring rate.

Liquid segregation behaviour of a semi-solid squeeze cast A356 aluminium cup-shaped part

ABSTRACTIn this study, the effects of pouring temperature (solid fraction of primary particles) on the structure and liquid segregation behaviour of a cup-shaped semi-solid rheocast processed casting made from the A356 aluminium alloy were investigated. Results showed that the solid fraction of primary particles at the bottom of the castings was greater than in other parts of the castings, and the highest liquid segregation occurred in the mid-height (wall) of the castings. Liquid segregation was increased with an increase in the initial solid fraction of primary particles. The critical solid fraction at pouring for minimum liquid segregation was found to be approximately 25%.This paper is part of a thematic issue on Light Alloys.

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.

Research on Microstructure and Mechanical Properties Evolution of Rheocast and Thixocast 319s Aluminum Alloy

In semi-solid rheocast and thixocast industry, T6 heat treatment was one key factor to improve the mechanical properties of the castings. The microstructure evolution was closely influenced by heat treatment temperature and time. In this paper, the morphology change of eutectic silicon in semi-solid alloy during different heat treatment time was firstly observed. The changes of both roundness and aspect show that the silicon particles underwent fragmentation, coarsening and growing up processes during solution treatment. Then, the mechanical properties after stand T6 and T6 with higher temperature were compared. It may be concluded that the higher temperature doesn’t have obvious effect to increase the mechanical strength, but severe negative effect on the elongation. Finally, the incipient melting defect appeared in higher temperature T6 was proved and its relationship with elongation was analysed.

ESTUDIO COMPARATIVO DE LAS PROPIEDADES METALÚRGICAS Y DE LA RESISTENCIA A LA CORROSIÓN DE LA ALEACIÓN DE ALUMINIO EN AC-46500 OBTENIDA POR MOLDEO A PRESIÓN Y POR MOLDEO EN ESTADO SEMISÓLIDO

This article explores the new possibilities that injection moulding process known as Semi Solid Rheocasting (SSR) could offer, whose main innovation lies in the fact that the material is injected in semisolid state, whereas in the traditional method of casting (HPDC) the material is in liquid state. Although the process SSR is already stablished in some enterprises at the state level, the improvements that could have the components obtained by this process could lead to increased interest of new companies. The study is focused on the same alloy, the EN AC-46500, which is submitted to the processes mentioned above. A comparison between components obtained through both processes, have been done by means of the analysis of microstructural characteristics, mechanical properties and resistance to corrosion. The microstructure has been analysed by optical microscopy, using different solutions where have been submerged the samples to observe with greater clarity the grains and the components of the alloy. The samples have also been studied using scanning electron microscopy, with the purpose of establishing the type of breakage which have suffered after having been tested mechanically. The mechanical properties of the material, have been measured through mechanical tensile tests and by Charpys pendulum impact tests. Finally, accelerate corrosion tests have been done in a salt spray chamber and in a Kesternich or SO2 chamber to determine the resistance of the material against corrosion. At the same time, to confirm what has been observed in the corrosion tests mentioned, corrosion testing has been carried out with electrochemical tests to measure the rate of corrosion in the components object of this study. Key Words: EN AC-46500 alloy, Aluminium, Characterization, HPDC, injection moulding, SSR.

Laser Beam Welding of Semi-Solid Rheocast Aluminium Alloy 2139

NASA developed aluminium alloy 2139 for use in airframe structural applications as the requirement for higher strength, corrosion resistant, aluminium alloys is increasing, however the need to weld ‘unweldable alloys’ is also becoming apparent. 2139 is seen to be in this class. Semi-solid rheocast aluminium plates (Al-Cu-Mg-Ag) were cast in high pressure die casts. In total 27 welds were fabricated in experimentation, 3 on each plate to avoid distortion by using a continuous wave Nd:YAG. The weldability of this Al-Cu alloy was assessed by optical microscopy to indicate the quality and geometry of the passes. Comparisons were made with As-Cast (F) tempers. Laser power parameters ranged from 3 kW to 4 kW and weld speeds from 4 m/min to 6 m/min. Welds were allowed to cool naturally. The results show that by varying speed and power, when combined with heat treatments, produce diverse results for this unweldable alloy.

Optimization of degree of sphericity of primary phase during cooling slope casting of A356 Al alloy: Taguchi method and regression analysis

The present work presents the results of experimental investigation of semi-solid rheocasting of A356 Al alloy using a cooling slope. The experiments have been carried out following Taguchi method of parameter design (orthogonal array of L9 experiments). Four key process variables (slope angle, pouring temperature, wall temperature, and length of travel of the melt) at three different levels have been considered for the present experimentation. Regression analysis and analysis of variance (ANOVA) has also been performed to develop a mathematical model for degree of sphericity evolution of primary α-Al phase and to find the significance and percentage contribution of each process variable towards the final outcome of degree of sphericity, respectively. The best processing condition has been identified for optimum degree of sphericity (0.83) as A3, B3, C2, D1 i.e., slope angle of 60°, pouring temperature of 650°C, wall temperature 60°C, and 500mm length of travel of the melt, based on mean response and signal to noise ratio (SNR). ANOVA results shows that the length of travel has maximum impact on degree of sphericity evolution. The predicted sphericity obtained from the developed regression model and the values obtained experimentally are found to be in good agreement with each other. The sphericity values obtained from confirmation experiment, performed at 95% confidence level, ensures that the optimum result is correct and also the confirmation experiment values are within permissible limits.

Effect of Cooling Rate on Microstructure of Semi-Solid AZ61 Slurry Produced via Ultrasonic Vibration Process

The semi-solid metal (SSM) processing, including thixoforming and rheocasting, offers the opportunity to manufacture net-shaped components with complicated shape and good mechanical properties. More and more researches have been focused on rheocasting in recent years because of its low cost and high productivity [1,. Rheocasting involves stirring the solidifying alloy to prepare non-dendritic semisolid slurry, then shaping the slurry directly. Ultrasonic vibration (USV) has the potential to be a simple and effective process to produce semisolid metal slurry. Previous investigations have revealed that when USV is applied on the solidifying melt, microstructure changes occur involving grain refinement, increased homogeneity, reduced micro-segregation as well as degassing [3-.

Microstructure control of AZ31 alloy by self-inoculation method for semisolid rheocasting

A novel rheocasting process, self-inoculation method (SIM), was developed for the microstructure control of semisolid wrought Mg alloy. This process involves mixing between liquid alloy and particles of solid alloy (self-inoculants), subsequently pouring the mixed melt into a special designed multi-stream fluid director. The primary phase with dendritic morphology in the conventionally cast AZ31 alloy has readily transformed into near spherical one in the slurry produced by SIM from melt treatment temperature between 690 °C and 710 °C and self-inoculants addition of 3%–7%. Achievement of the non-dendritic microstructure at the higher melt treatment temperature requires more self-inoculants addition or decreases in the slope angle of fluid director. Primary phase in the slurry thus produced has attained an ideally globular morphology after isothermal holding at 620 °C for 30 s. The increasing holding time leads to decrease of shape factor but the coarsening of particle size. The spheroidization and coarsening evolution process of solid particles during the isothermal holding were analyzed by Lifshitz-Slyozov-Wagner (LSW) theory.

Evolution of the Solidification Microstructure of Rheocast High Purity Aluminium

High purity aluminium has been successfully rheocast using the CSIR-RCS system combined with high pressure die casting. Analysis of the as-cast microstructure by SEM and EBSD revealed the presence of in-grain substructures. These morphological features show that the overall growth mode of the globular grains during rheocasting is planar, but the presence of these features indicates that the solidification mode is cellular at some stages during the slurry production process. Cellular solidification is associated with unstable growth at the solid-liquid interface and is initiated and exacerbated by solute gradients between the melt and the newly formed solid. This high purity alloy exhibits the same cellular growth, indicating that even minor solute variations have an effect on the stability of the solid-liquid interface and, hence, the mode of solidification during semi-solid rheocasting.

Melt Flow Type and Physical Model of Semisolid Rheo-Casting Process by Cooling Sloping Plate

In this paper, a physical model of semisolid rheo-casting process by cooling sloping plate is established, and the features and parameters of this process are analyzed. The calculation results show that there exists lamellar flow and turbulent flow on the sloping plate surface commonly. The critical transfer distance from lamellar flow to turbulent flow decreases with the increment of the initial flow velocity gradually. The critical transfer distance decreases with the increment of the sloping angle slowly. The effect of the sloping angle on the critical transfer distance is relatively not obvious.

Controlled Diffusion Solidification of 2024, 6082 and 7075 Al Alloys via Tilt-Pour Casting Process

Controlled diffusion solidification (CDS) is an innovative casting route for Al alloys to obtain a cast part with a non-dendritic morphology of the primary Al phase during solidification, similar to those obtained in the semi-solid rheocasting process. The process involves mixing two alloy melts with specific individual compositions and temperatures to produce the desired final alloy by mixing and immediately casting in a mould. CDS enables sound shaped casting of Al based wrought and cast alloys with a non-dendritic microstructure. The two pre-cursor alloys will have to be chosen from a critical study of the various isopleths of the multi-component phase diagrams for the respective alloys along with laboratory experiments. Further, the favorable melt superheat temperatures of the two pre-cursor alloys were evaluated from laboratory experiments as well. A tilt-pour mould designed and validated to cast tensile test bars was used for the study. The aim of the study was to demonstrate the feasibility of manufacturing sound shaped castings via the CDS route for alloys which have been impossible to shape cast in a permanent mould process due to the detrimental hot-tearing problem during solidification. The present work defines process conditions to enable shaped casting of the Al wrought alloys 2024, 6082 and 7075 by the tilt-pour casting technique. Sound casting and a favorably non-dendritic microstructure were obtained for these alloys during solidification in a ceramic crucible as well as in a metallic mould via the tilt-pour casting process. Further work is underway to optimize various process conditions and develop new heat treatment cycles for parts cast by CDS to maximize mechanical properties for these alloys.

Semi-solid near-net shape rheocasting of heat treatable wrought aluminum alloys

Flexibility of the CSIR-RCS, induction stirring with simultaneous air cooling process, in combination with high pressure die casting is successfully demonstrated by semi-solid rheocasting of plates performed on commercial 2024, 6082 and 7075 wrought aluminum alloys. Tensile properties were measured for the above mentioned rheocast wrought aluminum alloys in the T6 condition. The results showed that tensile properties were close to or even in some cases exceeded the minimum specifications. The yield strength and elongation of rheocast 2024-T6 exceeded the minimum requirements of the wrought alloy in the T6 condition but the ultimate tensile strength achieved only 90% of the specification because the Mg content of the starting alloy was below the commercial alloy specification. The strengths of rheocast 6082-T6 exceeded all of the wrought alloy T6 strength targets but the elongation only managed 36% of the required minimum due to porosity, caused by incipient melting during solution heat treatment, and the presence of fine intermetallic needles in the eutectic. The yield strength of rheocast 7075 exceeded the required one and the ultimate tensile strength also managed 97% of the specification; while the elongation only reached 46% of the minimum requirement also due to incipient melting porosity caused during the solution heat treatment process.

The effect of injection conditions on the structural integrity of the components produced by semi-solid Rheocasting

This work is a contribution to improve understanding about the behaviour of components produced by semi-solid processes. The present study shows the effect of different conformation parameters on automotive cranking cover production obtained by Semi-Solid Rheocasting Process (SSR®). The components were produced using EN AC-46500 alloy, by an industrial plant with a 700 Ton HPDC machine and an IDRA SSR Station.