Solid State Phenomena Vols. 192-193

Abstract: The relatively high costs of processing titanium alloys and the high variability in the products' quality currently represent the major economic obstacles to using such materials in either production or medical engineering. For this reason, new research and development work at the Institute for Metal Forming Technology of the University of Stuttgart is pursuing the objective of improving and enhancing pre-existing processes for these types of materials. In doing this, aspects are considered which specify definite mechanical properties during and after the forming process as well as reduce the costs by means of cutting the manufacturing times, increase the use of semi-finished products and minimise finishing operations.

Abstract: Based on several years of research, this paper presents some approaches on industrial installation on thixoforging steel with an important potential of an innovative technology. The possibility of Thixoforging industrialization makes it possible to consider new steel components production. From billet to final part with complex shape obtained in one step, several “keys” are developed as heating system, transfer system, part and die design.

Abstract: The aim of this work is to evaluate the thermal and mechanical loadings applied to the tools during steel thixoforming process in order to determine appropriate tool materials and solutions. This evaluation was realized thanks to experimental trials and to the finite elements simulations. The effect of these loadings on the tool’s failure modes are highlighted and compared to the ones observed in classical forming processes. Beyond this, the failure modes of different tool materials and solutions are presented. The tested materials are hot-working tool steels. Other possibilities and tool coating or surface treatments are discussed as well.

Abstract: Heat treatment of rheo-high pressure die cast (R-HPDC) A356 brake callipers has produced good mechanical properties on the laboratory scale. An industrial heat treatment is required to evaluate the applicability and conformance of the R-HPDC A356 brake callipers to the automotive industry. This research studied A356 brake callipers heat treated on the industrial scale with particular emphasis on the resulting microstructure, hardness and tensile properties. The eutectic Si-particle spheroidisation after solution heat treatment was achieved and observed with optical microscopy. A hardness increase from 64 to 100 Vickers was achieved from the as-cast condition to the industrially heat treated T6 condition. The heat treatment caused no significant variation in hardness and tensile properties from brake callipers within the same batch or from different batches. The yield and ultimate strengths of the industrial heat treated brake callipers were lower compared to the laboratory scale heat treatment properties, while the ductility increased, mainly due to quenching effects. Even though the industrial heat treated A356 brake callipers resulted in yield and ultimate tensile strengths lower than those achieved on a laboratory scale, they still exceeded the minimum specifications for gravity die cast A356 brake callipers.

Abstract: Recent studies regarding semi-solid casting as a viable alternative to conventional liquid metal casting have been met with considerable interest. The dual nature of semi-solid materials results in a marked decrease in internal defects otherwise associated with conventional casting methods. In recent years, the National Research Council Canada - Aluminum Technology Centre (NRC-ATC) has dedicated itself to better understanding the behaviour of semi-solid aluminum alloys, notably 357, using the SEED (Swirled Enthalpy Equilibration Device) rheocasting method. SEED is a novel process which relies on the mechanical agitation and cooling of molten aluminum to produce a semi-solid billet. This billet is then injected into a die to yield the desired cast shape. The current work focuses on the rheocasting of a 357 aluminum alloy support bracket, consisting of four rings. Material flow around a ring is known to result in a welding of the two metal fronts. Traces of porosity and oxides can sometimes be found at the weld, unless preventative measures are taken. These include the use of overflows attached to the ring via a web as well as a careful control of the casting parameters. At NRC-ATC, several parts were rheocast and then subjected to both destructive and non-destructive testing, in an effort to better understand the material flow behaviour around these rings. The results obtained are presented herein.

Abstract: This paper presents an analysis of a new rheocasting process suitable for the manufacturing of high performance automotive parts. The process is able for the realization of components using Al alloys. An important aspect is related to the possibility to obtain quite wide range of thicknesses, starting from 2.5 mm. The used alloy is the well known A356, with low Fe content, maximum 0.08 wt%. T6 heat treatments has been performed, while the soundness of the parts has been certified by non destructive tests. These parts are produced to be mounted on a top level and famous sport car. Non standard samples for mechanical tests have been machined directly from the components. Following the mechanical tests fracture surface analysis has been carried out by SEM to observe some morphological details and to evaluate the influence of the process and of the alloy conditions on the fracture behaviour. On the polished transverse sections of the samples morphological analysis has been performed. The obtained results shown high level of mechanical strength for all series of components. The reliability of the process is very high at a convenient level of manufacturing rate. The weldability of the parts has been demonstrated.

Abstract: Semisolid forging process, characterized by short process, near-net shape, low cost, and high performance, is increasingly playing an important role in lightweighting transportation systems for light metals. In this study, semisolid forging process for hypereutectic Al-Si alloy, as a substitute for nodular cast iron, was applied in producing automobile AC compressor components. The results showed that hypereutectic Al-Si alloy swash plate thixo-forged had higher strength than nodular cast iron one by optimizing forming process parameters.

Abstract: Commercial semi-solid cast impellers are produced from Al-Si-Cu alloys heat treated to the T6 temper. The study described in this paper involved the identification of casting and heat treatment parameters to produce semi-solid processed turbocharger impellers from a silicon-free, higher strength 201 alloy. Casting parameters were identified which minimized hot tearing in the alloy 201 impellers. A series of heat treatment studies were performed to determine optimum heat treatment parameters. The T71 temper was identified as the preferred heat treatment condition to produce high strength as well as superior elongation. The results from mechanical property measurements conducted on the T71 heat treated impellers are reported. Optical and scanning electron microscopy (SEM) were also used to characterize the microstructure of alloy 201 impellers before and after heat treatment, and representative microstructures are presented.

Abstract: The aim of this work was to evaluate the advantages in using semisolid processing of Al-Sn alloys in order to improve microstructural homogeneity and, consequently, wear resistance. Different tests were performed on an Al3Sn4Cu by using ultrasound treatments during solidification to obtain an almost globular microstructure. Metallurgical characterizations and pin on disk wear tests were carried out on semisolid as well as on conventionally cast samples in order to assess the benefit of the treatment.

Abstract: Ternary Mg-based thermoelectric materials are prepared by Semi-Solid Processing (SSP) and Spark Plasma Sintering (SPS). DTA, XRD and SEM analysis are applied to explore the processing conditions of Mg2Si1-xSnx (x=0, 0.2, 0.4, 0.6, 0.8, 1). The results show that raw-materials should be put into the furnace at 773 K, and kept 60 min in 1123 K. Then stirring 5 min under semi-solid state and air cooled finally. At temperature of 1023 K, pressure of 30 MPa, the sample is sintered by SPS. The XRD shows that the peaks of sample are sharp and complete, and move left with increasing Sn. The thermoelectric properties of Mg2Si1-xSnx (x=0.4, 0.6) are analyzed between 373 K to 673 K. Results indicate that electrical conductivity (σ) increases continually, Seebeck coefficient (α) increases then decreases, and thermal conduction (κ) decreases and increases with increasing temperature. Except that, electrical conductivity and Seebeck of Mg2Si0.6Sn0.4 are better than Mg2Si0.4Sn0.6 made by the same method. The properties of Mg2Si0.4Sn0.6 sintered at 1023 K, is better than the one at 973 K. The maximum zT of Mg2Si0.4Sn0.6 is 0.086 at 573 K.