Solid State Phenomena Vols. 116-117

Abstract: To aid the optimizing design of filling system, computer simulation technique is introduced to predict injection-forming process and to protect defects during trial manufacture of automotive parts by using semi-solid die cast process. By comparing formed appearance of parts in experiments and that in simulations, and observing the relationship between internal defects inspected by X-ray and flow field obtained in simulation, it is indicated that there are quite good agreements between simulation and experiment, right predictions for cast defects resulting from filling process can be made and improving direction is proposed. The realization of numerical visualization for filling process of high speed during semi-solid die cast process will play an important role in optimizing technology plan and process.

Abstract: Melt extrusion is a new fabrication process with the characteristics of both casting and extrusion. In this process, a metallic melt which is poured and solidified up to semisolid state in the container can be directly extruded through the die exit to form a product of bar shape without other intermediate processes. The effects of various process parameters, such as melt temperature and extrusion ratio, on the extrusion behavior of Al-Cu alloys in the semisolid state were investigated. Mechanical properties of the melt extruded Al-Cu alloy were measured and its characteristics are compared with the microstructure and copper contents in the alloy. Al-Cu alloys were successfully extruded after squeezing out of liquid during the melt extrusion with smaller force (60 Mpa) compared to the solid extrusion. Al-Cu alloys bar with the mean grain size of 200 μm was fabricated by melt extrusion; however, the mechanical properties have nothing to do with the extrusion ratio. The squeezing out of liquid was get lead to the segregation of the alloys and was affect on the mechanical properties.

Abstract: Uniaxial compression tests on semi-solid AZ61 alloy fabricated by stain-induced activation (SIMA) process and the conventional casts were carried out using the Gleedle-1500 dynamic material testing machine. The relationships between stress and stain were analyzed. The numerical relationships among processing parameters (strain rate z ε&
strain z ε
temperature T
liquid volume fraction L f ) and stress were studied. The proposed constitutive equation was established for semi-solid AZ61 magnesium alloy using the multiple nonlinear regression method. A scientific basic provided for both numerical simulation of processing process of semi- solid AZ61 alloy and rational choice and control of processing parameters.

Abstract: Thixotropy is the most important characteristic of semi-solid materials, and it is decided by the variation of microstructure during action of handling. In this paper, for the sake of the industrial thixoforming and numerical simulation, microstructure and stress variation of semisolid magnesium alloys during isothermal compression is researched. Here, samples are heated to the desired temperature in the empty space with various holding times and compressed horizontally. Stress–strain curves during compression can be given directly by the experimental computer, and each of curves show a peak stress in a small strain and then decrease rapidly, which originally because of the thixotropy of semisolid materials. Moreover, thixotropy of semisolid magnesium alloys is clearer with the evolution of microstructures including agglomeration and deagglomeration of solid particles and the moving way of liquid at different places and strain under different conditions. Microstructures during isothermal compression show that the deagglomeration of solid particles increase with increasing the strain rate, therefore, the thixotropy of semisolid magnesium alloys increases. However, when solid volume fractions are lower, the agglomeration of solid particles doesn’t change obviously with increase or decrease factors, meaning that the thixotropy is smaller. Relationships between thixotropy and microstructure at other different conditions are also given according to the experiments and analysis.

Abstract: By a high-temperature Couette type viscometer, we studied the thixotropic behavior of the semi-solid AZ91D magnesium alloy slurry. According to different variable conditions, we could measure the change of the shear stress. The results showed that the shear stress of semi-solid AZ91D magnesium alloy slurry increased at starting shearing, and the shear stress fell down at the maintained shear rate shearing. In our experiment data, we found that the semi-solid AZ91D magnesium alloy slurry had the behavior of shear thinning fluid. As the maximum shear rate increased, the measured shear stress increased at a dissimilar level. When the rising time was shorter, the increasing range of shear stress was larger. As the shearing time of the maintained shear rate increased, the falling down degree of the shear stress increased and it can be presented as a function of shearing time, such as: e 0.0159t min 11331 τ = − . At the same shear rate, the area of hysteresis loop was bigger and the thixotropic behavior was more obvious.

Abstract: Filling and solidification phenomena during thixoforming of copper rotor for small sized induction motors have been analyzed and characterized by experiment and computer simulation. Forming defects in slots of thixoformed rotor were examined by microstructural observation. Most filling and solidification failures were mainly related to complexity in slurry flows through slots in rotor core. Computer simulation with single slot model showed the effects of die temperature and ram speed on the filling characteristics clearly. Simulations with flow guide model showed that the control of filling velocity of slurry at slot and the consideration of possible differences in flow velocity in each slot are important.

Abstract: The surface tension and the viscosity characteristics of molten metal are the most important factors in casting process and metallic foam manufacturing especially. The surface tension (by the modified ring method) and the viscosity (by the rotational method) of molten Al-Cu alloys have been measured under high purity Ar gas atmosphere. The surface tension and the viscosity of Al-Cu alloys were investigated in the temperature range of 660-800oC, and the effects of the additional elements were investigated at the 660~680
. The result show that the surface tension and viscosity of these alloys decrease with increasing temperature together. The viscosity of Al-Cu alloys near the melting point is about 4.7 to 5.7 [mPa.s]. The effect of additional thickening elements has the tendency that is the surface tension decreased and the viscosity increased. This anomalous behavior has the relation of the preferential adsorption of high activity elements on the surface.

Abstract: This paper uses the small punch test (SPT) to some performance of the materials, have put forward basic method to test the material tensile mechanics performance from an inverse FE method with SPT. The research shows that some tensile mechanics performance and stress of each district of welding seam can be accurate determined by small punch test. This research has offered the theoretical foundation for characterizing of the welded joint with mechanical heterogeneity

Abstract: In this study, in order to develop the cast product of Al alloy having a globular microstructure by using the elctromagnetic (EM) stirrer, which was specially designed and manufactured to induce a various fluid flow type of melt during solidification, a morphlogy and size of primary solid phase of the solidifying slurry was investigated with respect to EM stirring condition such as an induced magnetic flux density (MFD) and a frequency of input current. The magnetic flux density of EM stirrer was measured by using a gaussmeter and its distribution and magnetic force within Al melt was simulated in ANSYS program. The induced MFD was increased with decreasing a frequency of input current at the same input voltage due to the increased penetrating depth of magnetic field. But, the magnetic force related directly with a stirring strength of melt was increased with the frequency. Both a roundness and size of primary α phase of Al alloy was decreased with increasing a frequency of input current and MFD within the experimental range. Therefore, the primary α phase was refined and globularized at the higher frequency and MFD.

Abstract: Current practice in designing tooling components for semisolid processing requires extensive commitments of human resources. Even when utilizing currently available Computer Aided Design (CAD) systems, tool design remains a complex task requiring large amount of design knowledge. Considerations such as part material, tool material, characteristics of die filling, flow behavior of semisolid slurries must be carefully thought by the tool designer to reach an acceptable tooling solution. This paper proposes the framework for computer assisted tool design by integrating tool design domain knowledge into CAD system to help tool designers.