Semi-Solid of Alloys and Composites XV

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Authors: Merton C. Flemings
Abstract: A summary is given of the history of our understanding of dendrite coarsening, including particularly fragmentation. Much is now understood about this process as it takes place in directional solidification of a quiescent melt. Much less is understood about it in the rapidly cooled, turbulent environment of semi-solid casting. The importance of dendrite fragmentation in semi-solid processing is that it is key to obtaining fine final grain size, grain spheroidicity and rapid production rate. I have chosen in this keynote paper to talk about the fundamentals of an important part of the semisolid casting process ... that of “dendrite fragmentation.” The paper is written with an eye to its possible practical usefulness to researchers in process innovation. If we understood the dendrite fragmentation mechanism better, could we achieve finer, more numerous, grains than we do now? Could fully non dendritic structures be obtained industrially in short processing times?
Authors: Annalisa Pola
Abstract: Since the very first production trials, it was evident that semi-solid components exhibit excellent mechanical properties, comparable to those of forged material and, in any case, better than permanent mold castings. Over the years, these findings have been confirmed by many authors. Most of the papers available in scientific literature deals with the demonstration of this improvement, especially in order to show the reliability of new and alternative production routes. On the contrary, only some studies focus their attention on the relationship between enhanced mechanical properties and the microstructure. However, it is demonstrated that the increased performance of semi-solid components is not only due to the absence of porosity, but there is a clear relationship between microstructure and properties. This paper reports about the state of knowledge in this subject, in particular for what concerns tensile, fatigue, wear and corrosion resistance.
Authors: Johannes Winklhofer
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.
Authors: Shu Sen Wu, Du Yuan, Qiang Chen, Shu Lin Lü, Zhi Wei Huang
Abstract: Generally nano-SiC particles are difficult to be added into molten aluminum metals because of poor wettability. Nano-SiC particles reinforced A356 aluminum alloy composites were prepared by a new process, i.e., a molten-metal process combined with mechanical stirring at semi-solid state and ultrasonic vibration method. The nano particles were β-SiCp with an average diameter of 40 nm, and pre-oxidized at about 850°C to form an oxide layer with thickness of approximately 3.6 nm. The SEM analysis results show that nano-SiC particles are dispersed well in the matrix and no serious agglomeration is observed. The tensile strength and elongation of the 2wt.% nano-SiCp/A356 composite in as-cast state are 259 MPa and 5.3%, and they are improved by 20% and 15% respectively compared with those of the A356 alloy.
Authors: Bai Wei Zhu, Salem Seifeddine, Anders E.W. Jarfors, Peter Leisner, Caterina Zanella
Abstract: This paper aims to investigate the anodising behaviour of Al-Si components produced by rheocasting, to understand the effect of the surface liquid segregation (SLS) on the anodising response. The material investigated was EN AC 42000 Al-alloy with an addition of 150 ppm Sr. The component was rheocast and conventionally liquid cast for benchmarking. The RheoMetalTM process was used to prepare slurry and subsequently cast using a vertical pressure die casting machine. Prior to anodising, mechanical grinding was used as pre-treatment method for selected samples as comparison with components in the as-cast state. Anodising was performed on the components using a constant controlled voltage at 25 V, in 1 M H2SO4, at room temperature. The duration of anodising was varied from 30 mins to 120 mins to examine the relationship between oxide layer thickness and the anodising time. The oxide layer was investigated and characterised. The results demonstrated that the presence of the SLS layer, which was enriched with alloying elements, had a significant influence on the anodising behaviour of the cast component. The oxide layer thickness of the components produced by rheocasting and fully liquid casting was measured and compared. The relations between the oxide layer thickness and anodising time, as well as the casting methods are presented and discussed in this paper.
Authors: Yi Meng, Hui Min Zhou, Jia Lin Gan, Sumio Sugiyama
Abstract: The application of semisolid forming (SSF) is inhibited significantly by the inhomogeneous distributions of microstructure and mechanical properties in the products manufactured by SSF. Beside of forming parameters including forming temperature, isothermal holding time, and forming speed, post heat treatments of SSF is one of the most important facts affecting the microstructure and mechanical properties of the SSF-manufactured products. In this study, heat treatments including annealing, quenching, and tempering different experimental conditions were conducted on the SKD11 tool steel samples manufactured by multi-stage thixoforming with different forming parameters. The microstructures in different regions of specimen processed by different experimental conditions were investigated by using a field-emission scanning electron microscopy (FE-SEM), an energy-dispersive X-ray spectroscopy (EDS), and X-ray diffractometer (XRD). Base on the results of microstructural analyses, the microstructural evolution of SKD11 tool steel during multi-stage thixoforming and subsequent heat treatments with varies experimental parameters were discussed and summarized. Meanwhile, the relationship between microstructure and mechanical properties of SKD11 tool steel processed by multi-stage thixoforming and subsequent heat treatment was also discussed.
Authors: Laura Schomer, Mathias Liewald
Abstract: Interpenetrating Phase Composites (IPC) belong to a special subcategory of composite materials and reveal enhanced properties compared to the more common particle or fibre reinforced composite materials. However, as the use of conventional manufacturing processes creates structural deficits, these IPC are not able to exploit their complete potential. In this respect, infiltration of open-pore bodies from alumina with an aluminium alloy in the semi-solid state offers great perspectives for manufacturing of IPC. In this context, this paper is focusing on significant structural characteristics of metal-ceramic IPC produced in this way by using a tool with an open die cavity. Thereby, the macroscopic mould filling, possible damage of the ceramic body, the residual porosity, the filling of microporosity of the cell walls and possible interface reactions depending on the thermal parameters of the manufacturing process were investigated in this paper.
Authors: Chong Lin, Shu Sen Wu, Shu Lin Lü
Abstract: The influence of high pressure and manganese on Fe-rich phases (FRPs) and mechanical properties of Al-14Si-2Fe alloy with rheo-squeeze casting (RSC) were investigated. The semi-solid alloy melt was prepared using ultrasonic vibration (UV), then formed by squeeze casting (SC). Results shows that the FRPs in as-cast Al-14Si-2Fe-(0.4,0.8)Mn alloys with SC are composed of coarse plate-shaped δ-Al4(Fe,Mn)Si2, long needle-shaped β-Al5(Fe,Mn)Si and bone-shaped α-Al15(Fe,Mn)3Si2 phases when the pressure is 0 MPa. During the solidification of the alloys with RSC, the FRPs are first refined by UV, then furtherly refined as the pressure increases. With RSC, the FRPs in Al-14Si-2Fe-0.8Mn alloy are finer and rounder than that of the Al-14Si-2Fe-0.4Mn alloy under the same pressure. The FRPs in RSC Al-14Si-2Fe-0.8Mn alloy are mainly granular particles with an average diameter of about 12 μm under 300 MPa. For the alloy with the same composition, the ultimate tensile strength (UTS) of RSC sample is higher than that of the SC sample. Under the same forming process, the UTS of Al-14Si-2Fe-0.8Mn alloy is higher than that of the Al-14Si-2Fe-0.4Mn alloy.
Authors: Mnel A. Abdelgnei, M. Zaidi Omar, Mariyam Jameelah Ghazali
Abstract: Earlier work has shown that Al-5.7Si-2Cu-0.3Mg aluminium alloy is suitable for thixoforming process. Here, the dry sliding wear behaviour of the alloy, in the as-cast and thixoformed conditions were investigated. The cooling slope technique was used to produce the alloy with globular microstructure for the thixoforming process. Both the thixoformed and cast samples were subjected to T6 heat treatments prior to the wear tests. The tests were carried out using a pin-on-disc tribometer, against a hardened M2 tool steel disc of 62 HRC at different loads, under dry sliding conditions at fixed sliding speed and sliding distance of 1 m.s–1 and 5 km respectively. The microstructural response, worn surfaces were thoroughly and carefully examined using various methods such as scanning electron microscopy, energy dispersive spectroscopy, and differential scanning calorimetry. The density of the heat treated thixoformed alloys showed significant increase in the hardness property, among others, due to its reduced porosity. Their wear test results also observed that the weight loss of materials increase with an increase in the input load and the sliding distance for all samples. However, the as-cast alloy displayed higher wear rate compared with the thixoformed alloys. In general, the wear mechanisms showed a mixture of abrasive, oxidative and delamination wear (mild wear) at low applied loads and mainly an adhesive (severe wear) at high applied loads.

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