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Thermo-mechanical finite element analysis was carried out to study the deformation behavior and temperature distribution during equal channel angular pressing (ECAP). The material model used is the Johnson-Cook constitution model that can consider the multiplication effect of strain, strain rate, and temperature on the flow stress. The effects of pressing speed, pressing temperature, workpiece material and die geometry on the temperature rise and flow behavior during ECAP process were investigated. The simulated temperature rise due to deformation heating was compared with published experimental results and a good agreement was obtained. Among the various die geometries studied, the two-turn die with 0° round corner generates the highest and most uniform plastic strain in the workpiece.

The temperature rise and temperature distribution in the workpiece during equal channel angular pressing were investigated by using the finite element method for Al–1%Mg and Al–3%Mg at different pressing speeds. The simulated temperature rise was compared with published experimental and analytical results.

A well-designed runner and gating system is very important to secure good quality die castings through providing a homogenous mould filling pattern. Numerical simulation is a cost-effective tool in the design of runner and gating systems to visibly analyse the mould filling process. A thin-walled magnesium telecommunication part was selected to be hot chamber die cast and a numerical simulation technique was applied for the optimisation of the runner and gating. Two types of runner and gating systems were designed and analysed. A preliminary design with a split gating system led to a swirling filling pattern and insufficient central flow, which prematurely closed the edges and left the last filled areas falling into the inner portion of the part. It resulted in a high possibility of air entrapment in the casting and the design was not proper for the part. The design was improved by using a continuous gating system and a bigger size runner. The gate area was increased and the gating speed was slightly reduced. Numerical simulation showed that the new design provided a homogenous mould filling pattern with the last filled areas being located at the upper edge of the part, where overflows and vents were conveniently attached. For the study, die inserts for both designs were fabricated. A series of casting experiments were conducted. The short shot filling tests proved that the simulation results matched the actual casting results very well. Good quality thin-walled telecommunication parts with sound microstructure were produced based on this optimised runner and gating system.

High pressure die castings usually contain gas porosity due mainly to the entrapment of air or gas in the melt during the very high speed injection of the molten metal into the cavity. In this paper, the advantages of using an evacuated die cavity during mould filling were evaluated. ASTM standard die casting tensile specimens of three Al alloys, Al–5%Si, Al–8%Si and Al–18%Si, were cast on a Buhler shot control die casting machine equipped with a Fondarex vacuum assist system. The effect of vacuum assistance on the porosity distribution and mechanical properties of the produced castings were studied in detail. Selected specimens were also subjected to a T6 tempering treatment to evaluate the formation of surface blisters and effects on the mechanical properties. It was found that the volume of gas porosity and the pore sizes in the castings were significantly reduced by using vacuum assistance during die casting. As a result, the density and the mechanical properties, particularly the tensile strength and ductility, were improved markedly. An optimum injection speed was also identified for producing high performance castings. After heat treatment, vacuum assisted die cast parts showed much less surface blistering when compared to conventional die cast parts, demonstrating that vacuum assisted die castings are promising for heat treatment at elevated temperatures to improve the mechanical properties.

We propose and demonstrate experimentally a novel design of single-electron quantum dots. The structure consists of a narrow band gap quantum well that can undergo a transition from the hole accumulation regime to the electron inversion regime in a single-top-gate transistor configuration. We have observed large size quantization and Coulomb charging energies over 10meV. This quantum dot design can be especially important for scalable quantum computing., Comment: 5 figures

Optical properties of deep level EL2 in LEC, HB and VPE GaAs have been investigated by using photocapacitance technique. It indicated that EL2 in various GaAs samples has slightly but definitely different optical properties. Such phenomena further demonstrate the reasonableness of the concept of “EL2 family”.

Seven electron traps and two hole traps have been detected on various n-InP samples of high-quality Au/InP Schottky barrier and p + n junction structures by using DLTS technique. We propose that electron trap ME 1 (E C -0.69eV) observed for the first time is related to impurity iron, and the commonly detectable electron trap ME 2 (E C -0.62eV) is probably caused by native defect or residual impurity other than iron.