P.K. Seo

Microstructural characteristics and mechanical properties of hypo-eutectic and hyper-eutectic Al–Si alloys in the semi-solid forming process

Abstract The characteristics of the globularization distribution and quantitative mechanical properties in the forming process of rheologically formed parts with an arbitrary shape need to be investigated to minimize occurrence of defects and to minimize subsequent machining. However, most of relevant research that has been performed is about the effects of die temperature and applied pressure on the filling behavior of semi-solid materials. Therefore, in the present study, the microstructures and mechanical behavior of Al–Si materials with wear resistance fabricated by the rheological forming (semi-solid forming) process are evaluated in terms of globularization and surface non-uniformity. The effect of alloy compositions and heat treatment on the mechanical properties is investigated for a part fabricated using the rheological forming process. The three-step reheating process for rheological forming was performed with wrought and cast aluminum alloys. The mechanical properties of the parts so formed are obtained for several locations by the tensile test and microstructure investigation.

Numerical analysis by new proposed coil design method in induction heating process for semi-solid forming and its experimental verification with globalization evaluation

Abstract In this paper, four procedures for optimizing inductive coil design are presented to reduce computational time and lead time. First, a theoretical coil design is proposed by defining the quantitative relationship between billet length and coil length. Second, the numerical simulation of the induction heating process using a general purpose finite element analysis code, ansys , is carried out to predict the temperature distribution. Third, an objective function on the basis of the optimization process for the coil design is proposed by introducing an optimization technique. Finally, the results of the optimal coil design are also applied to the induction heating process to obtain a fine globular microstructure. The proposed objective function based on the computational techniques and numerical simulation model would contribute to producing thixoformed parts with good mechanical properties and reducing lead time.

The effect of test specimen size and strain-rate on liquid segregation in deformation behavior of mushy state material

Abstract For optimization of net shape forging process with semi-solid materials (SSMs), it is important to predict the deformation behavior of material. In this study, compression experiments have been performed to investigate the deformation behavior of SSM with variation in processing parameters such as test specimen size and strain-rate. Stress–strain curves and microstructures of SSM were investigated. The characteristics of flow between solid and liquid phase considering liquid segregation is examined through the above experiments. Moreover, porosities were measured to evaluate the effects of experiment parameters on liquid segregation quantitatively.

The effect of globular microstructure size on the mechanical properties in reheating process of aluminum alloys

One of the important steps in semi-solid forming is the process of reheating raw materials to the semi-solid state. This process is not only necessary to achieve the required semi-solid state of the billet, but also to control the microstructure of the billet. In the reheating process, the globule size is determined by the holding time of the final reheating step. Therefore, some experiments to investigate the relationship between the mechanical properties and the holding time in the last heating step were performed. The alloys used in this experiment were 357, 319, and A390 alloys. The experiments of reheating were performed using an induction heating system with a capacity of 50 kW. This article shows the evolution of the microstructure according to the holding time of the last reheating stage. Furthermore, to evaluate the effect of globule size as determined by holding time of the final reheating step, uniaxial tension tests were performed. The stress-strain curves were plotted according to the holding time, and a relationship between the microstructure and the flow stress of semi-solid material was formulated.

Mechanical characteristics evaluation of hollow shape part with metal matrix composites fabricated by thixoforging process

Abstract Thixoforming process has been accepted as a new method for fabricating the net shaped metal matrix composites (MMCs) with lightweight and wear resistance. In this paper, the effect of volume fraction and reinforcement sizes on mechanical properties in cylinder liner part of MMCs has been investigated with processes parameters such as pressure and velocity. Moreover, the methods to obtain the thixoforged composites cylinder liner with high quality has been proposed. To evaluate the composites cylinder linear fabricated at the conditions proposed, mechanical properties of fabricated composites cylinder linear were compared with those of commercial composites cylinder linear.

Reheating Process of Metal Matrix Composites for Thixoforming and Their Inductive Coil Design

In this work, the fabrication processes of particulate metal matrix composites (PMMCs) with a homogeneous distribution of reinforcement and their reheating for thixoforming were studied. Electromagnetic stirring was used to fabricate PMMCs to vary particle size. PMMCs were tested before and after the reheating process using a tensile test with and without heat treatment. The combined process conditions for fabricating the PMMCs are also suggested for a variety of particle sizes. For the thixoforming of PMMCs, fabricated billets are reheated by using an induction heating system with a maximum capacity of 20 kW. The effects of the dispersion state of the reinforcements on the reheating temperature and microstructural morphology were investigated.