Papers by Keyword: Semi-Solid

Abstract: Semi-solid processing over a cooling slope has emerged as an efficient technique for producing near-spherical grain structures in metallic composites. In this study, an Al-15Mg₂Si-4.5Si composite processed using this method exhibited globular Mg₂Si particles embedded within an α-Al matrix. The addition of 0.01% Sr further refined the microstructure by reducing the size of the Mg₂Si particles, acting as a grain-refining agent. To gain deeper insight into the effect of Sr addition on microstructure evolution during semi-solid processing, a two-dimensional phase field model is developed. Wherein, rather than modelling the nucleation of Sr-containing phases explicitly, the influence of Sr is realised by modifying the relevant phase field parameters. The simulations predicted key microstructural characteristics—including grain size, sphericity, area fraction and grain density of P-Mg₂Si —along with interfacial energy and mobility coefficients for both the base and Sr-modified composites. The phase field results show good agreement with experimental observations, validating the modelling approach. Keywords: Semi-solid, Magnesium silicide, Phase field, grain refinement

Abstract: In the automotive industry, casting products produced by high pressure die casting are essential. Due to the higher mechanical demands on these castings, the technological requirements of the process are also increasing. Therefore, the control of the microstructure and the development of defects play a major role. High pressure die casting parts made of aluminium usually contain gas porosity due to gas compression during the filling process of the cavity and the intensification during solidification. The use of semi-solid casting thus opens new doors to fulfil promising future demands. In this study, the venting system was adapted to the Rheometal^TM process of aluminium and designed in the form of gaps, thus ensuring better venting. Subsequently, the results obtained were compared with casting process simulations to highlight possible differences.

Abstract: The continuous demand for lightweighting vehicles leads to a significant increase in the use of aluminium alloys in the automotive sectors. The Al-Si-Mg aluminium alloys are widely applied in foundry processes to produce structural components, due to their high specific mechanical properties combined with good castability and corrosion resistance. Primary (from bauxite) alloys are often used to ensure the highest quality of such parts, nevertheless their production route causes high CO₂ emissions. With the goal of reducing cradle-to-grave emissions of vehicles secondary (from recycling) Al-Si-Mg alloys are often used for cast products, however their percentage of impurities is considered too high for structural components. Lately, some Al-Si-Mg recycled alloys with a low content of Fe are available on the market as an alternative to primary alloys. Alongside the traditional foundry processes, semi-solid techniques are known to be able to increase the performance of Al-Si alloys. In this paper, a preliminary microstructural and mechanical characterization of secondary A356 alloys, manufactured by the ultrasound semi-solid method, was performed. In detail, both high Fe and low Fe recycled A356 alloys were investigated in comparison to the traditional primary one. The effect of the T6 heat treatment was also taken into account.

Abstract: It is easy to occur solid-liquid separation during semi-solid rheological forming, which leads to poor uniformity of microstructure and properties and limits its application in high strength and toughness parts. In this paper, a semi-solid CuSn10P1 alloy slurry was prepared by an enclosed cooling slope channel (for short ECSC). The effect of ingate length on microstructure and properties by semi-solid squeeze casting was studied. The results showed that the proper increase of the length of the ingate is beneficial to improve the uniformity of the microstructure and properties of the semi-solid squeeze casting. The microstructure uniformity and properties are the best when the ingate length is 20mm. The ultimate tensile strength and elongation of semi-solid squeeze casting CuSn10P1 alloy with 20 mm ingate length reached 419.2 MPa and 13.4%.

Abstract: Owing to their several attractive features such as high hardness, high elastic modulus, light weight, high strength to weight ratio, high thermal conductivity, and high temperature strength, composites from Al-Mg₂Si family offers promise towards deployment in several industries such as automobile, aerospace, marine, defence and electronic. The present molecular dynamics (employing LAMMPS) based simulation study is one of the first attempt to investigate the nucleation and grain growth mechanisms of Mg₂Si phase at atomic level in case of novel Al-15Mg₂Si-4.5Si composite, during semi-solid processing. Modified embedded atom method (MEAM) potential has been used to study the atomic interactions in the composite. Reaching the melt state at 1000 K, the temperature of the system is first decreased from 1000 K to 853 K and then the system is held at 853 K for 100 ps. The simulations are performed with three different cooling rates. With lowering of temperature, randomly distributed Mg and Si atoms form atomic clusters at arbitrary locations within the system, which is the nucleation stage for Mg₂Si phase formation. Cluster size, radial distribution function has been used to investigate the structural evolution of Mg-Si clusters. Cooling rate significantly influences the grain size as well as the grain growth kinetics. The information about the thermodynamic state of the system has been revealed by extracting the values of internal energy, enthalpy, specific heat. during the slurry preparation and isothermal holding stages. The growth mechanism of Mg₂Si nucleus has been characterized from the temporal variation of (Mg + Si) atoms taking part in the cluster formation. Power-law variation is observed in the cooling stage whereas a linear variation is observed in the isothermal stage.

Abstract: Based on the theory of grain refinement, the microstructures and simulations of A356 semi-solid aluminum alloy under different cooling mediums were studied. The experiment and simulation results show that water cooling is better than any other cooling mediums. Combined with the simulation of stirring and heat dissipation in SIT device, the changes of temperature field and solid fraction of the melt were studied to help understand the nucleation, growth and solidification behavior under the SIT process. During the process, the temperature field of the melt becomes relatively uniform from a larger temperature gradient and the continuous cooling speed is increased. The results also indicate that compared with traditional casting, the microstructure cooled by water are composed of refined rosiness and nearly spherical particles. With the increase of cooling degree, the average grain size decreased from 206μm to 186μm. The solid fraction increases from 4.4% to 12.2% under the no-cooling and air-cooling conditions, while it is more uniform, increasing from 5.1% to 8.8% due to the water cooling.

Abstract: The semi-solid extruded CuSn10P1 alloy bushings were homogenization annealed. The effects of annealing process on the hardness and wear properties of bushings were researched. The results show the Brinell hardness increases firstly and then decreases with the increase of annealing temperature and annealing time. With the annealing temperature increasing, the grinding loss rate and friction factor decrease firstly and then increase. At the annealing time of 120 min, the grinding loss rate decreases from 7% at the annealing temperature of 450 °C to 6% at 500 °C, and then increases from 6% at 500 °C to 12% at 600 °C. The friction factor decreases from 0.54 to 0.48 and then increases to 0.83. At the annealing temperature of 500 °C, the grinding loss rate decreases from 11% at the annealing time of 60 min to 6% at 120 min, and then increases to 15% at 150 min. The friction factor decreases from 0.67 to 0.48 and then increases to 0.72. The best wear performance and Brinell hardness can be obtained at annealing temperature of 500 °C for 120 min.

Abstract: It is easy to form reverse segregation and shrinkage porosity defects during the solidification of CuSn10P1 alloy, which leads to the poor properties and limits its application in high strength and toughness parts. In this paper, semi-solid CuSn10P1 alloy slurry was prepared by enclosed cooling slope channel (for short ECSC). The effect of runner distance on microstructure and properties by liquid squeeze casting and semi-solid squeeze casting was studied. The results showed that the microstructure of semi-solid squeeze casting is finer than that of liquid squeeze casting, and the shrinkage defects are improved. The solid fraction with 65 mm runner is lower than that without runner in liquid squeeze casting and semi-solid squeeze casting due to the retention effect of solid phase in semi-solid slurry flow, but the properties with 65 mm runner is better than that without runner. The ultimate tensile strength, yield strength and elongation of semi-solid squeeze casting CuSn10P1 alloy with 65 mm runner distance reached 466.5 MPa, 273.6 MPa and 13.4%, which were improved by 26%, 19% and 97%, respectively, as compared to that of liquid squeeze casting.

Abstract: Spherical morphology is the typical characteristic of the microstructure in semi-solid slurries, while the formation mechanism of these spherical grains is still unclear, especially the migration of the solid-liquid interface under different process conditions. This study will focus on the effect of pouring temperature and swirling on the morphology of grains. A phase field-lattice-Boltzmann method using parallel computing and adaptive mesh refinement (Para-AMR) was employed to study the FCC α-Al phase evolution in binary Al-Si aluminum alloy. Study results represent that the pouring temperature has a significant influence on the morphology of the α-Al grains. Low pouring temperature is a benefit for the formation of spherical microstructures. And the swirling can refine the microstructure under high pouring temperature.

Abstract: Semi-solid 6061 aluminum alloy slurry was prepared by a graphite serpentine channel and its rheo-diecasting experiment was carried out on the slurry. The influence of pouring temperature on the microstructure evolution and mechanical properties of the rheo-diecasting were investigated. The microstructure and fracture mechanism of traditional die cast tensile specimens and rheo-diecast tensile specimens were compared and investigated. The results indicate that the microstructure of rheo-diecast tensile specimens is composed of spherical primary α-Al grains and fine secondary solidified α₂-Al grains. When the pouring temperature increased from 660 °C to 720 °C, the average equivalent grain diameter of primary α-Al grains increased from 42 μm to 58 μm, and the shape factor decreased from 0.82 to 0.73. As the pouring temperature increases, the as-cast tensile strength and elongation of tensile specimens both increase first and then decrease. When the pouring temperature was 690 °C, the best mechanical properties were obtained, with as-cast tensile strength of 142.93 MPa and as-cast elongation of 4.86%. The fracture mechanism of traditional die casting is mainly ductile fracture, and the fracture mechanism of rheo-diecasting is a mixed fracture of intergranular fracture and ductile fracture.