Papers by Keyword: Semi-Solid Forming

Abstract: Aluminium matrix composites (AMCs) offer improved mechanical and tribological properties compared to monolithic materials and therefore provide great potential for various applications. This particularly applies to particle-reinforced AMCs revealing comparatively high contents of reinforcement particles. However, these types of composites are difficult to manufacture due to their abrasive characteristics as well as their complex rheological material behaviour. An approach to produce such AMCs is semi-solid powder processing, combining powder pressing and sintering in one step in order to produce fully dense composites with currently only cylindrical shapes. Therefore, the tools as well as the powder mixture are first heated into the semi-solid temperature range of the aluminium powder and subsequently formed using low pressures under 200 MPa. Due to the shear thinning behaviour of the semi-solid aluminium matrix the porous structure of the pressed powder is filled during compaction, resulting in homogenous particle distributions in the component. However, this process results in high process times as well as energy costs, due to the heating inside of the die. In contrast to the semi-solid powder processing in one step, in this paper, a novel process route combining cold uniaxial compaction of particle reinforced aluminium powders having up to 50 vol.% SiC with subsequent semi-solid forming is presented. Here, a particle reinforced and cylindrically shaped green body is utilized as raw material, in order to produce complex components through semi-solid forming. The parts produced in this way are featuring varying wall thicknesses and are used in order to determine the process limits for manufacturing particle reinforced components having up to 50 vol.% SiC. Thereby, the influence of reinforcement particle size as well as particle loading on the homogeneity of the resulting particle distribution of an academic component is investigated. Future main objective of the process route is the manufacturing of complex parts with homogenously distributed particles.

Abstract: In the context of increasing needs for lightweighting vehicles, semisolid casting of aluminium components is a proven route that can be efficiently applied for automotive parts. Although semisolid forming has not yet reached the market penetration that suits its actual potential, it is currently and efficiently used in many applications around the world on a daily basis. An example of such will be shown. This paper presents a case study on the application of the SEED rheocasting technology for the casting of an engine bracket. The part is made of the widely used AlSi7Mg0.3 alloy and is heat treated in T6 condition to benefit from the enhanced mechanical properties made possible by semi-solid forming. Throughout the development phase, different aspects associated with semisolid casting, such as slurry condition, gate design, mold filling behaviour, lubrication, blistering and others, were addressed successfully. In the final, the combination of the SEED technology with a thorough development process and the specific casting rules for semi-solid forming led to actual commercial production and contributed to weightsaving on the actual part as compared to a former design made from high pressure die casting.

Abstract: The following paper deals with the production of Interpenetrating Phase Composites (IPC) using semi-solid forming technology. Therefore, adequate ceramic foams were selected and infiltrated by processing the aluminium alloy A356 in the semi-solid state. In the studies presented in this paper, the infiltrations of two ceramic materials (Al₂O₃ and SiC) with three different pore sizes (10, 20 and 30 ppi) were investigated. During the forming process the liquid phase fraction of the aluminium was varied to analyze infiltration effects in relation to the raw material´s liquid phase fraction. Afterwards, microsections of the produced specimens were analyzed in order to characterize their microstructure and the quality of infiltration. The results showed that completely filled composite components with good mechanical properties can be produced by infiltrating ceramic preforms with a semi-solid aluminium alloy.

Abstract: AZ91D magnesium alloy is one of the most widely used magnesium alloys in the production of metal forming, which use the characteristics from liquid state to solid state of metal to form. The present status of the research and application of the semi-solid forming for AZ91D magnesium alloys at present was reviewed in this paper, including the microstructural characteristics, the thixotropic and rheological behavior, the forming process of semi-solid for AZ91D magnesium alloys and the mechanical properties of the parts made of semi-solid magnesium alloys. The developing prospects and the key points of the semi-solid forming for AZ91D magnesium alloys were forecasted, and the industrial application of the alloy were also discussed.

Abstract: The trend towards lightweight construction in automotive engineering causes additional effort and higher expense in vehicle manufacturing, because new materials or, respectively, new material combinations require adapted production and processing methods. Various combinations of metallic and fibre-based structures (GRP-/ CFRP components) presuppose convenient joining methods. In this context, an innovative joining method for combining sheet metals with carbon textiles is going to be developed at the Institute for Metal Forming Technology (IFU, University of Stuttgart / Germany). The goal of this research work is motivated by the prevention of any damage of the used textile fibre structures during the joining process (compared to mechanical joining methods like screwing or riveting). Based on the semi-solid forming technology, the new joining process is going to be developed to create a material integrated interlock between fibres and metallic components.This paper deals with the first fundamental investigations, conducted at IFU, which have already shown the technical feasibility of this new type of joining technique. The research work to be carried out comprises the usage of different sheet alloys: the combinations steel-aluminium, aluminium-aluminium and steel-steel are to be joined with layers of carbon fibre fabrics. By this innovative joining method, a firmly bonded and non-aging connection between textile and metallic materials is to be produced, without the need of any adhesive materials or associated preparative cleaning methods.

Abstract: The main goal of investigations on semi-solid metal processing is to produce complex parts with enhanced mechanical properties. Flow behavior and die filling in semi-solid processing is an intrest area of researchers. A comprehensive understanding of the behavior of the under investigation metallic slurry is the design key of a successful manufacturing process. In this way the material’s transient response is very important for understanding of the rheological properties and also further commercial development of the process. The material used in this research is an Al-Si alloy which is widely used in automotive and aerospace applications. The experiments were conducted using a Searl rheometer which is specially designed for high temperature rheological measurements. For rheological tests of semi-solid alloy in different solid fractions, the isothermal holding and shear rate step change experiments were examined. Using practical rheological results, a single phase thixotropic model has been derived and adopted with measurements. The investigated alloy behavior was obviously thixotropic which is quantified in a theoretic model. Also instantaneous rheopectic behavior was observed for this alloy. The state of the microstructure has been applied through a structural parameter. The presented model for A356 alloy fits well with the experiments.

Abstract: To research the effect of electromagnetic stirring process parameters on the parts’ quality in semi-solid forming of aluminum alloy, the material of ZL017 was heated and melted, and electromagnetic stirred under different frequency and power, then material microstructure gained by different process parameters was observed. The elementary alteration rule of fluid field was analyzed with the alteration of stirring frequency, current density, stirring time，stirring temperature and fluid viscosity. Suitable process parameters for electromagnetic stirring of ZLl07 was concluded.

Abstract: The SEED technology, a rheocasting process based on the slurry-on-demand approach, is an emerging technology that was developed in the mid-2000s. Many publications with regard to the process and to alloy development using this technology were made since, and several industrial units are operated worldwide. Moreover, the process is still actively developed and is fully supported by a team of scientists, engineers and technicians. With a global objective of addressing the user requirements and the industry needs, works were conducted toward optimization of the process and equipment. At first, the focus was on developing a simplified version of the SEED process to eliminate the so-called “drainage” phase while preserving the prime quality of the slurry produced. Improvement of some system components and integration of new features were also targeted to secure the overall equipment efficiency (OEE) and increase the process reliability. This work, backed with the optimization of process parameters and comprehensive techniques adapted for semi solid casting, led to the consolidation and even improvement of the properties of the parts produced for the common foundry alloys 356/357 and 319. Furthermore, the non-drained SEED version was applied to the validation of the process capabilities for uncommon cast alloys with works on 6061 wrought alloy, Duralcan metal matrix composite, and others. The results confirmed that the SEED process can efficiently be used in non-drained mode and achieve the same quality of slurry as the drained version originally developed. It is now proven in the industrial scale and actually integrated in the updated industrial equipment. Moreover, the capabilities of the process for special alloys and applications are still the subject of active development works.

Abstract: Materials with good mechanical properties and low density are characteristic for lightweight constructions in automotive and aerospace application as well as in the building industry. For this reason, the manufacturing of composite and hybrid materials is in focus of academic and industrial research. Because of the complex and expensive manufacturing process, the application of composite and hybrid materials in many cases is confined to niche and custom-made products. Therefore, the Institute for Metal Forming Technology (IFU) is concerned with the development of new processes for the manufacturing of metal matrix composites and hybrid components by semi-solid forming. Fibre reinforced AlSi-alloys are produced by the application of laminates made of alternating metal matrix layers and carbon fibre fabrics. Hybrid components are manufactured by the integration of higher-strength materials in the semi-solid forming process of aluminium alloys. Here, the main challenge is the integration of the reinforcing components without damaging due to high thermal and mechanical loads that are affecting during the process. These research activities are not only interesting for the mechanical engineering, but also for the civil engineering as this paper will reveal.

Abstract: The mechanical properties of 206 alloys are among the highest of aluminum alloys. However, these alloys are usually prone to hot tearing. It is known that the addition of silicon can reduce the hot tearing propensity and improve fluidity. However, the commercial 206 alloys used in conventional casting processes limit the silicon concentration ≤0.05 wt% to obtain good mechanical properties. However, the semi-solid forming offers a unique opportunity to increase the silicon content to improve the castability without compromise on mechanical properties. In the present paper, the development of modified 206 alloy compositions to minimize hot tearing during semi-solid forming while maintaining competitive mechanical properties is reported. The effect of high silicon contents with varying copper levels on hot tearing sensitivity is studied. The mechanical properties of a high Si 206 alloy with lowest hot tearing sensitivity are evaluated. It is found that increasing the silicon content in 206 alloys is beneficial to reduce hot tearing. The high Si 206 variants produced by the SEED rheocating process not only reduce significantly the hot tearing sensitivity but also attain superior mechanical properties.