To improve the industrialization of the process, the study of a thixoforming line stability was proposed. The thixoforming line is fully automated to optimize the repeatability of the experiments. Parameters of the heating cycle, the slug temperature, the tool temperature and the forming speed were studied. For each of them, a range of the expected variations in a steady-state process as well as the effects of these variations on the process itself (forming load and parts quality) were given. These variations are shown to be acceptable. Three different tools were used in the experiments. Some mathematical simulations were realized on the finite elements code Forge2008© with a semi-solid constitutive law. The capacity of the model to represent the process stability was discussed. The simulation results are in agreement with the experiment results.

Electro-pulse modification (EPM) was used to change the dendritic structure of AlSi₇Mg alloy to globular one. The effects of the modified temperature, electro-pulse frequency and time on the solidified structure were examined. The results show that these parameters play an important role in the solidified microstructures. That is to say, under the same modified temperature, the solidified microstructure will be improved greatly with the increase of electro-pulse frequency and time, but when they exceed to limit values, the solidified microstructure will become worse, resulting from the decrease of the ratio of nucleation. The experimental results indicate that the suitable modified temperature of AlSi₇Mg alloy is 720 °C, and the appropriate electro-pulse frequency and time are 5 Hz and 40 s, respectively. Then the microstructures produced by suitable EPM process were reheated at temperatures between liquidus and solidus, the primary-Al grains ripen further and become more spherical, which is favorable to the semi-solid forming of AlSi₇Mg alloy.

When treated in pressure die casting processes the semi-solid aluminum alloys demand resilient cores which can bear the stress occurring during filling and the final pressure phase. The design of permanent cores is highly restricted in order to maintain removability. Lost cores provide the possibility of complex, undercut geometrical shapes which is mandatory for a variety of casting components. However, eligible materials which show appropriate resilience and proper decomposition properties at the same time, and in the upper echelon of cost-effectiveness, are seldom known. With the semi-solid process suited between HPDC and GDC regarding the core stress, several common and economically efficient lost core systems could be used. A selection of potentially suitable materials was identified and tested. The range of testing comprises widespread sand core-systems (amin-pur-coldbox and CO₂-water-glass) as well as materials less commonly used, namely salt, plastic and zinc. Different types of conditioning are applied to enhance the surface properties. The mechanical properties of the sand cores are enhanced by different heat treatment methods during curing. The cores are tested producing a research component cast on a HPDC machine with semi-solid A356 slurry fabricated in the cooling channel process. The cast component was analyzed regarding shape stability, core removability and surface as well as the structure quality. The results show the importance of the surface conditioning for the sand-cores while salt and zinc produce good parts comparable to the reference steel core quality.

Thixoforging of steels is a potential forming technology, which aims at producing near-net-shaped components with good quality from high strength steels in one forging step. The thixoforging process parameters such as billet temperature, temperature distribution after reheating, argon gas pressure, transportation time and forging load were investigated on the thixoforging of non axis-symmetric parts of steel grade X210CrW12. The experimental and numerical study of the material flow and tool temperature load reveal the areas of intensive tool wear, thus being useful for further tool design. Hardened hot working steel X38CrMoV5-1 as a tool bulk material with protecting thin films of TiAlN/g-Al₂O₃ shows good experimental results at 170 forging cycles.

The development work for producing an automobile component by thixocasting using A356.2 alloy was introduced. As the first step, the alloy was electromagnetically stirred and solidified to produce a billet with non-dendritic microstructure. The microstructure depended on several process parameters such as stirring intensity, stirring frequency, cooling rate, and melt initial superheat. Through a series of computational studies and controlled experiments, a set of process parameters were identified to produce the best microstructures. Reheating of a billet with non-dendritic microstructure to a semisolid temperature was the next step for thixo-casting of the components. The reheating process was characterized for various reheating cycles using a vertical-type reheating machine. The induction heating cycle was optimized to obtain a near-uniform temperature distribution in radial as well as axial direction of the billet, and the heating was continued until the liquid fraction reached about 50%. These parameters were determined with the help of a computational fluid dynamics (CFD) model of die filling and solidification of the semisolid alloy. The heated billets were subsequently thixo-cast into automobile components using a real-time controlled die casting machine. The results show that the castings are near net shape, free from porosity, good surface finish and have superior mechanical properties compared to those produced by conventional die casting processes using the same alloy.

The effects of the casting factors such as nozzle size to pour the melt, nozzle height, tilt of the slope and slope length, of the cooling slope on the process to make semisolid slurry were investigated. The results show that these factors affect the behaviors of the semisolid slurry on the cooling slope. The tilt of the slope is the factor that has major influence on the behavior of the semisolid slurry. The cooling roll is developed from the result of the research of the cooling slope. The rotating cooling roll can improve the sticking of the semisolid slurry on the substrate and it is suitable for making the semisolid slurry.

The hypoeutectic Al-Si alloy billet with non-dendrite was reheated to meet the needs of the semi-solid thixoforming microstructure by four kinds of reheating power, achieving the same final temperature of 851 K. Subsequently, under the same condition of thixoforming, the microstructure, surface hardness and tensile properties were observed. Afterwards, quantitative analysis was made for the microstructures of the reheated semi-solid of billet and the thixoforming parts. The results show that when the induction reheating power is 90 kW, the average grain size of the semi-solid billet is the minimum, the microstructures of the thixoforming samples also are the finest, and the mechanical properties of the relevant thixoforming samples are the best. Furthermore, after studying on the relationship between the microstructures of the semi-solid billet of aluminum alloy and the mechanical properties of the thixoforming samples, the reverse design of microstructure is primarily achieved. Finally, the effectiveness of the reverse design for semi-solid microstructure is confirmed by an actual automobile part with complex shape.

The semi-solid metal forming using high pressures has been applied for several years. In contrast, low pressure casting, such as gravity sand casting, has not been widely studied even though it may help reduce porosity defects and offer a better casting yield. A semi-solid gravity sand casting process using the Gas Induced Semi-Solid process was investigated. The results show that the process can produce complete parts with no observable defects. The ultimate tensile strength and elongation data of semi-solid cast samples are higher than those of the liquid cast samples. In addition, the semi-solid sand casting process gives a better casting yield. It can be concluded that the semi-solid sand casting of an aluminum alloy using the GISS process is a feasible process.

The rapid development of electronic packaging industry has resulted in higher requirement for packaging materials. The packaging material of SiC reinforced A356 aluminum alloy was fabricated by mechanical mixing method, and the SiCp/Al composite billet was formed by thixo-forging to manufacture the electronic packaging shell. The microstructure of the produced part was investigated. Two different thixo-forging procedures for manufacturing electronic packaging shell were analyzed. The results show that after being heated to 600℃ and held for 3 h, SiC_p has good compatibility with A356 aluminum alloy and the SiC_p/A356 composite billet can meet the requirements of thixo-forging. When the billet was remelted to 580℃, held for 10 min, the homogeneous microstructure with the best thixo-formability can be realized. The thixo-forging of electronic packaging shell is feasible.

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<φ_s<1), which involves the processing of alloys in the semi-solid state. Tooling has to be adapted to this particular process to benefit shear thinning and thixotropic behaviour of such semi-solid material. Tooling parameters, such as the forming speed and tool temperature, have to be accurately controlled because of their influence on thermal exchanges between material flow and tool. These thermal exchanges influence the high-cracking tendency and the rheology of the semi-solid material during forming, which affects parts properties and therefore their quality. Extrusion tests show how thermal exchanges influence quality of thixoforged parts made of 7075 aluminium alloys at high solid fraction by modifying process parameters like forming speed, tool temperature and tool thermal protector. Thus an optimum in terms of thermal exchanges has to be found between surface quality and mechanical properties of the part. A direct application is the evaluation of surface quality of thixoforged thin wall parts made of 7075 aluminium alloy.

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 6061 semi-solid aluminium alloy feedstocks prepared by near-liquidus casting were compressed in semi-solid state by means of Gleeble-3500 thermal-mechanical simulator. The relationship between the true stress and the true strain at different temperatures and strain rates was studied with the deformation degree of 70%. The microstructures during the deformation process were characterized. The deformation mechanism and thixo-forming properties of the semi-solid alloys were analyzed. The results show that the homogeneous and non-dendrite microstructures of semi-solid 6061Al alloy manufactured by near-liquidus casting technology could be transformed into semi-solid state with the microstructure suitable for thixo-forming which are composed of near-spherical grains and liquid phase with eutectic composition through reheating process. The deformation temperature and strain rate affect the peak stress significantly rather than steady flow stress. The resistance to deformation in semi-solid state decreases with the increase of the deformation temperature and decrease of the strain rate. At steady thixotropic deformation stage, the thixotropic property is uniform, and the main deformation mechanism is the rotating or sliding between the solid particles and the plastic deformation of the solid particles.

Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was performed. The results show that after as-cast AZ80 magnesium alloy is processed by equal channel angular extrusion, microstructure is refined well due to heavy dynamic recrystallization occurring in severe plastic deformation. Compared with semisolid isothermal treatment and conventional SIMA, semisolid billet with fine and spheroidal grains are achieved in new SIMA. Thixoforging process of semisolid billet prepared by new SIMA has many advantages such as good surface quality of final component, high ability to fill cavity and net-shape. The fine and spheroidal grains and high mechanical properties such as tensile strength of 298 MPa and elongation of 28% can be developed in final part thixoforged.

A damage prediction method based on FE simulation was proposed to predict the occurrence of hot shortness cracks and surface cracks in liquid-solid extrusion process. This method integrated the critical temperature criterion and Cockcroft & Latham ductile damage model, which were used to predict the initiation of hot shortness cracks and surface cracks of products, respectively. A coupling simulation of deformation with heat transfer as well as ductile damage was carried out to investigate the effect of extrusion temperature and extrusion speed on the damage behavior of C_sf/AZ91D composites. It is concluded that the semisolid zone moves gradually toward deformation zone with the punch descending. The amplitude of the temperature rise at the exit of die from the initial billet temperature increases with the increase of extrusion speed during steady-state extrusion at a given punch displacement. In order to prevent the surface temperature of products beyond the incipient melting temperature of composites, the critical extrusion speed is decreased with the increase of extrusion temperature, otherwise the hot shortness cracks will occur. The maximum damage values increase with increasing extrusion speed or extrusion temperature. Theoretical results obtained by the Deform^TM-2D simulation agree well with the experiments.

The feasibility of semi solid processing of hypereutectic A390 alloys using a novel rheoforming process was investigated. A combination of the swirl enthalpy equilibration device (SEED) process, isothermal holding using insulation and addition of solid alloy during swirling was introduced as a novel method to improve the processability of semi solid slurry. The effects of isothermal holding and the addition of solid alloy on the temperature gradient between the centre and the wall and on the formation of α(Al) particles were examined. In additional tests, phosphorus and strontium were added to the molten metal to refine the primary and eutectic silicon structure to facilitate semi solid processing. The results show that the combination of the SEED process with two additional processing steps can produce semi-solid A390 alloys that can be rheoprocessed. The microstructure reveals an adequate amount of non-dendritic α(Al) globules surrounded by liquid, which greatly improves the processability of semi-solid slurry.

Significant progress has been made in recent years in understanding and modelling the rheology of semi-solid metals. These models show the effects of the microstructure in terms of size and morphology of globules on the material response. More recently it has been shown that semi-solid metals can behave as compacted granular materials such as sand. A particular signature of such deformation is that the deformation becomes concentrated into shear bands which are 10−20 grains wide. Such bands have also been observed in a range of cast products. Recently, it has been clearly shown that shear bands in high pressure die cast (HPDC) products are also the results of Reynolds dilatancy. Shear bands are also known to be a common feature in semi-solid metal products. The segregation banding in semi-solid metal (SSM) material and its dependence of plunger velocity were investigated. Shaped castings were made with the RHEOMETAL™ process with a range of different plunger velocities. The microstructural characteristics were investigated, with a particular emphasis on shear bands. It is shown that ingate velocities influence the location and characteristics of the shear bands.

The feasibility of semi-solid die casting of ADC12 aluminum alloy was studied. The effects of plunger speed, gate thickness, and solid fraction of the slurry on the defects were determined. The defects investigated are gas and shrinkage porosity. In the experiments, semi-solid slurry was prepared by the gas-induced semi-solid (GISS) technique. Then, the slurry was transferred to the shot sleeve and injected into the die. The die and shot sleeve temperatures were kept at 180 °C and 250 °C, respectively. The results show that the samples produced by the GISS die casting give little porosity, no blister and uniform microstructure. From all the results, it can be concluded that the GISS process is feasible to apply in the ADC12 aluminum die casting process. In addition, the GISS process can give improved properties such as decreased porosity and increased microstructure uniformity.

An aluminum extrusion process is mainly used to fabricate long tubes, beams and rods for various applications. However, this process has a high production cost due to the need for investment of high-pressure machinery. The objective of this work is to develop a new semi-solid extrusion process using semi-solid slurry at low solid fractions. A laboratory extrusion system was used to fabricate aluminum rods with the diameter of 12 mm. The semi-solid metal process used in this study was the gas induced semi-solid (GISS) technique. To study the feasibility of the GISS extrusion process, the effects of extrusion parameters such as plunger speed and solid fraction on the extrudability, microstructure, and mechanical properties of extruded samples were investigated. The results show that the plunger speed and solid fraction of the semi-solid metal need to be carefully controlled to produce complete extruded parts.

The effect of pouring temperature, electromagnetic stirring power and holding process on semi-solid A356 aluminum alloy slurry was investigated, then the slurry was squeeze-cast. The results show that when the pouring temperatures are properly above the liquidus line, for example 630−650 °C, the slurry with spherical primary α(Al) grains can be prepared under the stirring power of 1.27 kW. The slurry is then homogeneously held for a short time, and the primary α(Al) grains are further ripened and distributed evenly in the slurry. The results of the rheo-squeezed casting experiments show that the injection specific pressure has a great effect on the filling ability of the semi-solid A356 aluminum alloy slurry, and the higher the injection specific pressure is, the better the ability for the slurry to fill the mould cavity is. When the injection specific pressure is equal to or above 34 MPa, the whole and compact rheo-squeezed castings can be obtained. The microstructure of the castings indicates that the shape, size and numbers of the primary α(Al) grains in different parts of the castings are highly consistent. After being held at 535 °C for 5 h and then aged at 155 °C for 12 h, the ultimate strength of the rheo-squeezed castings can reach 300−320 MPa, the yield strength 230−255 MPa, and the elongation 11%−15%.