Papers by Keyword: Thixocasting

Abstract: In this paper, both thixocasting and rheocasting of Al-7Si-0.6Mg alloy (EN AC 42200) for the same part was performed. It was found that rheocasting of Al-7Si-0.6Mg alloy show a smaller primary Al grain size and significant improvement of cast defects compared with thixocasting of Al-7Si-0.6Mg alloy. This paper demonstrates that rheocasting of Al-7Si-0.6Mg alloy is more beneficial in terms of microstructure and cast defects compared with thixocasting of Al-7Si-0.6Mg alloy.

Abstract: In this paper, wear properties of samples manufactured using thixocasting were compared with those of components obtained using low-pressure die-casting and additive manufacturing in order to assess the relationship between material performance and production technologies, both conventional and innovative. The investigated items were made with AlSi7Mg alloy. First, microstructural analysis and hardness measurements were carried out. Subsequently, pin-on-disk wear tests were performed. Wear behavior of the samples was studied considering both coefficient of friction and wear rate, while the damage mechanism was analyzed by observation of the worn paths using scanning electron microscope, correlating the behavior to the specific microstructure. In addition, the effect of selected heat-treated conditions, relevant for real applications, on wear properties was also evaluated.

Abstract: An aluminum alloy, Al–4.8%Mg–2%Si, was cast by die casting and thixocasting, and the properties of the cast specimens were investigated. When the poured molten metal temperature was lower than 640 °C during die casting, it was lower than the liquidus temperature, and the metal became a semisolid slurry in the sleeve of the die casting machine; this fulfills the conditions for rheocasting. A tension test was conducted to investigate the effects of semisolid casting on the mechanical properties of Al–4.8%Mg–2%Si. The ultimate tensile strength and elongation of the ingots cast by die casting and rheocasting were affected by the size of ingot. When the ingot had a circular base of 4.5 mm diameter, the ultimate tensile strength and elongation were excellent; however, when the cross section of the ingot was a square with a side length of 20 mm, the tensile strength and elongation were inferior. The thixocasting was conducted using square ingots with a side length of 20 mm, and the tensile strength and elongation were poor in this case as well. The results of this study demonstrate that semisolid casting cannot improve the mechanical properties of Al–4.8%Mg–2%Si ingots with a high thickness. Semisolid casting cannot produce fine-grained Mg₂Si, and the mechanical properties of the material could not be improved by this casting method.

Abstract: Company SAG (Salzburger Aluminium AG) is a supplier of fuel tanks, LNG and hydraulic tanks, air reservoirs and structural applications for the commercial vehicle and automotive industry. The company’s expertise is welding but SAG also has a 25 years history in Semi-Solid casting starting in 1993 when the first Thixocasting cell was installed in Lend/Austria. Since then SAG is participating on the diverse casting market and competes with other processes looking for applications for which Semi-Solid processing has a unique selling proposition. This contribution gives examples of industrialized components and will outline their significant characteristics and advantages in comparison to conventional casting processes. Furthermore the development of Semi-Solid cast components, the production process chain as well as commercial aspects will be outlined. The bottom line is that usually it is not a single advantage of Semi-Solid casting that will make a product attractive for the customer but a combination of several of them. Moreover it is not just the casting process itself but the efficiency of the whole production process chain that will result in a commercially successful product.

Abstract: The feasibility of using the ultrasonic melt treatment to prepare billets for thixocasting process of hypoeutectic Al-7%Si alloys was studied in this paper. The work covered the billet preparation, soaking treatments and thixocasting process, with focus on the microstructural features in each case. The results showed that the use of ultrasonic treatment in billet preparation resulted in highly uniform, fine and non-dendritic microstructures. Billets with globule sizes as small as 58 µm, and roundness of more than 0.7 were obtained by ultrasonic melt treatment. Different soaking conditions before thixocasting were done and the optimum from which was the soaking for 5 min at 580°C, which resulted in thixocast parts with excellent combination of fine globules of 80 µm and roundness of 0.7 - 0.81. The eutectic Si, as well, was greatly refined by the ultrasonic thixocasting process. Furthermore, high-Fe ultrasonic treated billets, which were thixocasted successfully, exhibited Fe-intermetallic particles in highly desirable fine compacted form. These results reveal the feasibility and competence of UST as a potential route for feedstock production.

Abstract: 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.

Abstract: A general rule in conventional liquid metal casting processes is that smaller size would produce better metallurgical quality and mechanical properties. The conclusion that semi-solid thixocasting process doesnt follow this rule has been made recently. The microstructure and mechanical properties of semi-solid thixocastings are much less dependent on casting size and cooling rate than the liquid castings. The step casting in the previous study is specially designed and simplified. The practical castings, e.g. turbocharger impellers, are more complex than the step castings. In this work, the turbocharger impeller is used to study the impact of section size representing the casting size on the microstructure and mechanical properties of semi-solid thixocastings, compared with the step casting. Section thickness decreases from 50 mm to 3.5 mm. In addition, the impact of casting thickness on the eutectic phase is also presented. The results reveal that the size of primary α-Al particles is insensitive to the casting thickness in semi-solid thixocasting. The cooling rate has a notable impact on the size and geometric characteristics of the eutectic silicon particles, but the impact is reduced by the following T61 heat treatment. The association between the casting thickness and casting defects is discussed, in order to further understand the impact of casting size on durability and reliability of real casting components.

Abstract: Blistering is one of the main surface defects of thixocasting parts after solution treatment. In this paper, experimental study about the influence of plunger velocity on blistering problem was carried out, and the blistering level with various velocities was discussed. In addition, a series of simulation work for filling process were performed to analyse the formation mechanism of blister. The results indicate that the power law cut-off model can reflect the thixotropic characteristics better at shear rate range from 100s^-1 to 500s^-1 than Carreau model. Based on power law cut-off (PLCO) model, the filling process simulation reveals the air entrapments were caused by poor venting instead of turbulence, either decreasing the filling speed or modification of the die venting system would improve blistering problem.

Abstract: The thixocasting technology is chosen to produce the turbocharger impellers as it is capable of producing castings with high precision dimension, free of oxide and shrinkage porosity defects and therefore long service life. The thixocasting turbocharger impellers have the similar mechanical property to those produced by forging and machine processes, but much less costs. In the thixocasting process, the semisolid slurry with certain solid fraction is injected into mould at a high speed. Since high viscosity and thixotropic characteristics, the semisolid slurry reveals unique flow condition and characteristics in the filling process. So, its very desirable for the die design, process optimization, and defect control to visualize the high-speed filling process of semisolid slurry by numerical simulation. In this paper, several commonly used viscosity models for semisolid slurry are analysed. The Power law cut-off model (PLCO) model is selected to simulate the filling process in the thixocasting process of the impellers of 319s alloy, compared with actual results by partial filling testing. The causes of the casting defects are also analysed, indicating that the simulation results can accurately reproduce the filling process of semisolid slurry, and PLCO model is a successful choice for simulating the filling process of semisolid slurry with high solid fraction.

Abstract: Semi solid metal processing has numerous technical and economic advantages, such as viscous, non-turbulent flow (thus no air entrapment during casting), ability to fill ultra-thin sections (thus reduced part weight), little solidification shrinkage in the die (thus little or no porosity), minimum heat imparted to tooling (thus long tool life) and good response to T-5 aging (thus reduced heat treating costs). Still, SSM has never achieved a prominent position in the field of light metals casting Why Perhaps the reason was largely the down economy of recent years and SSM will yet emerge with the prominence once expected of it.