• Transactions of Materials Processing
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• v.8 no.3
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• pp.313-318
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• 1999

Many products related to automobile and airplane industry have been manufactured by semi-solid forging. In this paper finite element analysis of product by combined extrusion in semi-solid state was performed and its experimental verification using A356 was conducted. distribution of solid fraction was analyzed and compared with the experimental microstructure in the product. In addition, distribution of temperature in the product was analysed by finite element method.

• Journal of Korea Foundry Society
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• v.13 no.3
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• pp.248-258
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• 1993

A semi-solid alloy in which solid and liquid phase are co-existing is obtained by stirring of A17075 molten metal. A semi-solid alloy is dependent on the corresponding temperature within the solid-liquid range, and the process parameters should be controlled accurately to obtain the homogeneous semisolid alloy. The fabrication possibility of fiber-reinforced aluminum alloy containing $Al_2O_3$ short fibers with vigorous agitation of short fibers were obtained by control of stirring time, solid fraction and impeller speed in extrusion billet fabrication processes. The microstructure to extrusion billet fabricated by low pressure casting was investigated for fiber dispersion state. The relationship between the extrustion force and velocity at hot extrustion, the flow strain and extrusion ratio were theoretically described. The surface defects with lubricants and without lubricant after hot extrusion were investigated. The composites materials after hot extrusion were measured by vickers hardness with extrusion ratio. It has become clear that the secondary working such as hot extrusion was very useful to obtained improved the mechanical properties of metal matrix composites.

• Journal of Korea Foundry Society
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• v.34 no.3
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• pp.87-93
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• 2014

Thixo-extrusion of semi-solid 7075 aluminum alloy and the mechanical properties of its extrudates were investigated. The semisolid alloy was prepared by a cooling slope cast. In other to perform thixo-extrusion, semi-solid 7075 aluminum alloy billets were reheated at the reheating conditions reported in a previous study. The maximum extrusion pressure in thixo-extrusion was 615MPa. This was lower than that of conventional hot extrusion ($P_{max}=940MPa$) at the same extrusion conditions due to the increased fluidity of the alloy billet in the semi-solid state. The values of Rockwell hardness (scale B) at the extrusion direction of the as thixoextruded bar were 48~53HRB and the difference in Rockwell hardness between the transverse direction and the extrusion direction was 5HRB or less. The results show that thxio-extrusion of semi-solid 7075 Al alloy improves the workability and anisotropic with the extrusion direction compared with hot extrusion of the conventional alloy.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.04a
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• pp.23-26
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• 2003

Solid-state extrusion technique was employed for the improvement of mechanical properties of polylactic acid (PLLA) widely used as biodegradable internal fixation devices currently. Cylindrical billets were machined out from the vacuum compression-molded PLLA to have various diameters, and solid-state extrusion of the billets was performed at various drawing rates and at the extrusion temperature of $130^{\circ}C$. Throughout the whole processes the decrease in molecular weight was significantly suppressed to be about $10\%$. Flexural modulus and strength of PLLA increased up to 8.3 GPa and 221 MPa, respectively. Studies on the orientation and crystallinity of extruded PLLA could reveal the effects of billet morphology, draw ratio, and drawing rate on the flexural strengths of PLLA.

• Journal of Adhesion and Interface
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• v.15 no.1
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• pp.9-13
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• 2014

The purpose of this work is to investigate the specific gravity, thermal, and mechanical property changes of polypropylene (PP)/mica composites before and after solid-state extrusion. On increasing the filler content, the specific gravity of the composites increased. The specific gravity of the oriented specimen containing filler in PP matrix is found to be much smaller than that of pre-specimen due to the formation of more microvoids. The presence of microvoids in the case of oriented composite specimen significantly affected the tensile and flexural properties of the composites. Both flexural strength and modulus of the composites showed maxima when the mica contents was 10 wt%, regardless of the orientation via solid state extrusion.

• Transactions of Materials Processing
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• v.7 no.4
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• pp.364-374
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• 1998

It is the objective of this study to analyze the effect of various process variables on the quality of extruded product and extrusion force for semi-solid extrusion of Al2024 with solid phase structure of globular type by the finite element method. Process variables are initial solid fraction, ram speed, semi-angle of die, and reduction in area. The results of experiment are compared with those of simulation in order to verify the usefulness of the developed finite element program. The flow and deformation of semi-solid alloy are analyzed by coupling by coupling the deformation of porous skeleton and the flow of liquid phase. It is also assumed that initial solid fraction is homogeneous.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.06a
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• pp.5-15
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• 1997

It is the objective of this study that by conducting the serni-solid extrusion using A12024, the effect of various process variables on the quality of extruded product and extrusion force is understood. The results of experiment are compared with those of finite element simulation in order to verify the effectiveness of the developed FE-simulation code. In order to simulate densification in the deformation of serni-solid material, the semi-solid material is assumed to be composed of solid region as porous skeleton following compressible visco-plastic model and liquid region following Darcy's equation for the liquid flow saturated in the interstitial space. Then the flow and deformation of the semi-solid alloy are analyzed by coupling the deformation of the porous skeleton and the flow of the eutectic liquid. It is assumed that initial solid fraction is homogeneous. Yield and plastic potential function presented by Kuhn and constitutive model developed by Gunasekera are used for solid skeleton.

• Journal of Korea Foundry Society
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• v.24 no.6
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• pp.331-339
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• 2004

Melt-extrusion process, a metallic melt 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. In this study, the fabrication characteristics of the process were evaluated with various process parameters, such as preheating temperature of extrusion dies, extrusion temperature and extrusion ratio. AI-Cu alloys were successfully extruded after squeezing out of liquid during melt-extrusion with smaller force compared to the solid extrusion. Soundly AI-Cu alloy bar was fabricated at the preheating temperature of $500{\sim}520^{\circ}C$. The range of extrusion temperature for soundly melt-extruded AI-Cu alloy bar was increased with increasing extrusion ratio. Mechanical properties of melt-extruded AI-Cu alloy bars were found change with Cu content of the melt-extruded bars due to the occurrence of segregation. The various extrusion temperature yielded equiaxed structure with a grains size about 200 ${\mu}m$.

• Transactions of Materials Processing
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• v.8 no.4
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• pp.364-373
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• 1999

For material characterization of semi-solid materials, backward extrusion process, which has been used in forming of hollow-sectioned products, was analyzed by the upper bound analysis in the current study. The existing kinematically admissible velocity field was applied to steady state at which there was no change in the assumed regions of velocity field. For unsteady state, new velocity field, as a function of dead zone angle, was proposed. Through the whole analysis, fiction between die and workpiece was also considered. It has been studied how the process variables, such as friction factor and punch velocity, and material parameters, such as strength coefficient, strain rate sensitivity could affect on analysis results. Finally, by the comparison with the finite element analysis, the reliability and efficiency of the proposed velocity field were discussed.

• Transactions of Materials Processing
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• v.8 no.4
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• pp.374-383
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• 1999

To determine the flow stress of semi-solid materials, a new combined method has been studied by experimental and analytic technique in the current approach. Using backward extrusion experiment and its numerical analysis, the characterization scheme of semi-solid materials according to the change of initial solid volume fraction has been proposed. Because that solid volume fraction is sensitive to temperature change, it is required to precisely control the temperature setting. Model materials can guarantee the establishment of material characterization technique from the noise due to temperature change. Thus, clay mixed with bonded abrasives was used for experiment and the change of initial solid fraction was copied out through the variation of mixing ratio. Upper bound method was adapted to increase in efficiency of the calculation in numerical analysis and new kinematically admissible velocity field was employed to improve the accuracy of numerical solution. It is thought that the material characterization scheme proposed in this study can be applied to not only semi-solid materials, but also other materials that is difficult to obtain the simple stress state.