Solid State Phenomena Vols. 116-117

Abstract: An application of the semi-solid alloy Al-6Si-2Mg to produce automobile components was carried out for farther development of this new alloy. The experiments were done in a self-developed SSM trial line composed of semi-continuous caster combined with electromagnetic stirring for feedstock billet production, 6-station induction reheating equipment for restoring thixotropy of SSM billet and modified die-casting unit for semi-solid thixoforming. The results show that Al-6Si-2Mg alloy has such a suitable fraction solid and low temperature sensitivity of fraction solid that the controllability of SSM process is increased greatly. The billets have uniformly fine microstructure with a higher degree of sphericity and also retain good thixotropic properties. During thixoforming, the die is filled completely, the microstructure of components is dense, and the primary phases are near spherical, and the mechanical property after heat treatment has good performance.

Abstract: Aluminum-copper alloys offer both high strength and excellent ductility suitable for a number of automotive applications to reduce vehicle weight; however, the alloys are difficult to cast because of their tendency for hot tearing. In this work, semi-solid gravity casting of an aluminum-copper alloy, B206, was conducted in constrained rod casting molds to study the feasibility of using the process to reduce or eliminate hot tearing. To demonstrate the feasibility of gravity casting of the metal slurries, a fluidity test was also conducted. Results show that the hot tearing susceptibility of the aluminum-copper B206 alloy cast in semi-solid state is lower than those cast in liquid state with high superheat temperatures. The grain size of the semi-solid cast Al-Cu samples appears to be finer than those cast in liquid state with high superheat temperatures. In addition, the metal slurries had sufficient fluidity to fill the molds even with low gravity pressures. The results suggest that semi-solid gravity casting is a feasible process to help reduce hot tearing.

Abstract: Anodizing is widely used in the surface treatment of aluminium alloys in order to preserve the integrity of the alloy surface, to minimize the need for maintenance and repair, and to maximize the component life. The aim of this work is to study the influence heat treatments (T5 and T6) have on the anodization of A357 aluminium alloy produced by a Thixocasting process. In particular the effect of shape, size and distribution of silicon and intermetallic phases on the anodic oxide film formation. SEM and EDS analyses were used to examine the microstructural features found on, within and under the anodic oxide layer. Experiments using a tribometer (pin-on-disc tests) were performed in order to evaluate the friction and wear properties of the different layers.

Abstract: TiAlN/CrN multilayer coatings with an superlattice period of 6.1nm was applied to a proto-type high temperature segment mold for Cu semi-solid processing so that it was investigated the possibilities of TiAlN/CrN multilayer coating as a candidate protective coatings to extend the lifetime of high temperature molds and dies. Much improved performance was obtained from the TiAlN/CrN coated molds, although different behaviors were observed depending upon the type of substrate mold materials. . Improvement of mold performance was observed by TiAlN/CrN coating on AISI H13 steel, but TZM alloy with TiAlN/CrN coating was found to be the best candidate as a mold for high temperature Cu semi-solid processing.

Abstract: Water pump lid is selected as the automotive component to be cast using semisolid casting technology. Semisolid feedstock of alloy A357 was produced by a vertical continuous DC casting with electromagnetic stirring. Non-dendritic structure was obtained in the feedstock billets. A 6-station induction heating system was developed for feedstock billet reheating. Multi-stage reheating and well controlled reheating process resulted in a uniform temperature profile in the billet. Semisolid casting was carried out in a conventional high pressure die casting machine. Die design and casting parameters were adjusted to be suitable for semisolid casting. Compared with the conventional liquid melt casting, semisolid casting resulted in a much higher microstructural integrity with reduced shrinkage porosity.

Abstract: SSM is now considered an established technology to produce high integrity near net shape components for the automotive industry in particular. Although it is used extensively in the automotive industry, very little attention has been given to aerospace applications. SSM processing does demonstrate the potential to replace certain hogout components in commercial aircraft with the main aim to reduce costs while maintaining high strength to weight ratios. In order to achieve this it will require developing processes to reliably cast components with consistent properties to meet aerospace requirements. Since SSM forming is a relatively new process, materials properties data bases for components produced using this technique is very limited. One of the major challenges is the generation of a data base of material properties to assist design engineers for design of components, as well to assess the life expectancy and development maintenance schedules.

Abstract: It is well known that the family-mold has an advantage to reduce the overall production cost. However, defects are frequently occurred by an excessive packing the smaller volume cavity during molding, especially when the volumetric difference between two cavities is not negligible. Although the size of runner could be optimized by CAE analysis, the filling imbalance is hardly avoided in the actual injection molding process by various means. In this study, we confirmed the filling imbalance in a family-mold by the temperature and the pressure sensors, and developed a variable-runner system for balancing the cavity-filling. We carried out experiments of balancing the cavity-filling in the family-mold with the variable-runner system, and examined the effect of reduced cross-sectional area of a runner in the system. We examined the conditions of the shear rate and the viscous heating in the system with a CAE analysis. We also examined the influence of the injection speed and types of resins to the balancing-capability of the system in order to help mold designers easily adopt the variable-runner system to their design.

Abstract: Technology requirements for a billet micro globular structure development and following deformation are the basic inputs in a conceptual forging equipment design. The R&D team has studied the features of the Aluminum alloy thixoprocess experimentally on a crank press as well as with a help of computer simulation and have formulated requirements for SSM technology CNC prototype unit development.

Abstract: This study sought to examine the effect of various process parameters on the thickness of the amorphous strip produced by Planar Flow Casting (PFC), which is used to solidify molten metals rapidly. The processes were simulated via fully coupled fluid flow, heat transfer, and solidification models. The temperature distribution and velocity profile of melt in the computational domain with given process parameters were investigated according to various melt inlet temperatures, size of gap between nozzle slots, rotating wheel, and ejection pressure. In general, stable shaping of ribbons was obtained given a heat transfer coefficient of 100 cal/cm2/sec/°C. Strip thickness was found to decrease with the pouring temperature of melt. The results evaluated based on the numerical model were verified based on experimentally measured data.

Abstract: A functional automotive part, reaction shaft support, was fabricated by local squeeze and vacuum Diecasting (LSVD) with light-weight Al-15%Si hypereutectic alloy which has good fluidity and excellent wear resistance. The effects of local squeezing pressure and time-lag of LSVD process on the microstructure of the product were investigated. Measurement of specific gravity with the change of local squeeze pressure and time-lag showed that the local squeezing effect can be increased by increasing squeeze pressure and decreasing time-lag. However, too high a squeeze pressure and too a low time-lag brought about insufficient squeezing effect due to instant movement to the squeeze plunger stroke end point. Through the combination of vacuum suction before melt injection and local squeezing after melt injection in LSVD process, light-weight Al-15%Si alloy reaction shaft support was successfully developed, resulting in excellent microstructural and mechanical properties