• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1995년도 춘계학술대회논문집
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• pp.114-123
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• 1995

Hot workability and microstructural development of 7075Al alloy were studied by hot torsion test. With decling temperature from 440$^{\circ}C$ to 340$^{\circ}C$, and strain rate ranges form 5 ${\times}$10-3/sec to 5 ${\times}$10-1/sec , flow stress and microstructural development were analyzed . The hot resoration mechanism was found to be dynamic recrystalization (DRX) form the analysis of the flow curves and the microstructures. In multistage deformation with decreasing temperature grain refinement was obtained effectively compared to conventional thermomechanical treatment (TMT) process. The strain of the 1st stage deformation at 440$^{\circ}C$ was found to play an important role for the next stage deformation behavior at 380$^{\circ}C$.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.172-175
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• 2003

Thermomechanical behavior of Al-Mg-Si alloys have been studied to investigate the effect of microstructural features such as pre-existing substructure and distribution of particles on the deformation characteristics. The controlled compression tests have been carried out to get the basic information on how the alloy responds to temperature, strain amount and strain rate. Then hot forging of Al-Mg-Si alloys has been carried out and analyzed by the comparison with the compression tests. Microstructural features after forging have been discussed in terms of the thermomechanical response of Al-Mg-Si alloys. As already well mentioned, we have found that the deformation of Al-Mg-Si at the elevated temperature brought the recovered structure on most conditions. In a certain time, however, abnormally large grains have been found as a result of deformation assisted grain growth, which means that hot forging of Al-Mg-Si alloys could lead to a undesirable microstructural variation and the consequent mechanical properties such as fatigue strength.

• 소성∙가공
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• 제13권1호
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• pp.27-32
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• 2004

Thermomechanical behavior of Al-Mg-Si alloys was studied to investigate the effect of microstructural features such as pre-existing substructure and distribution of particles on the deformation characteristics. The controlled compression tests were carried out to get the information on how the alloy responds to temperature, strain amount and strain rate. Then hot forging of Al-Mg-Si alloys carried out and analyzed by the comparison with the compression tests. Microstructural features after forging were discussed in terms of the thermomechanical response of Al-Mg-Si alloys. As already well mentioned, we found that the deformation of Al-Mg-Si at the elevated temperature brought the recovered structure on most conditions. In a certain time, however, abnormally large grains were found as a result of deformation assisted grain growth, which means that hot forging of Al-Mg-Si alloys could lead to a undesirable microstructural variation and the consequent mechanical properties such as fatigue strength.

• 소성∙가공
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• 제10권1호
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• pp.35-41
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• 2001

The high temperature deformation behavior of SCM 440 can be characterized by the hot torsion test in the temperature ranges of $900^{\circ}C$~$1100^{\circ}C$ and strain rate ranges of 0.05/sec~5/sec. The aim of this paper is to establish the quantitative equation of the volume fraction of dynamic recrystallization (DRX) as a function of processing variables, such as strain rate ($\varepsilon$), temperature (T), and strain ('$\varepsilon$). During hot deformation, the evolution of microstructure could be analyzed from work hardening rate ($\theta$). For the exact prediction of dynamic softening mechanism the critical strain ($\varepsilon_c$), the strain for maximum softening rate ($\varepsilon^*$ and Avrami' exponent (m') were quantitatively expressed by dimensionless parameter, Z/A, respectively. The transformation-effective strain-temperature curve for DRX could be composed. It was found that the calculated results were agreed with the experimental data for the steel at any deformation conditions.

• 소성∙가공
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• 제31권2호
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• pp.64-72
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• 2022

Since aluminum alloys experience both tensile and compression deformation modes during forming process, it is important to understand the role of deformation mode on the hot formability of metallic alloys. In the present work, the hot formability of Al7050 alloy was investigated by conducting both tensile and Gleeble tests at various temperatures and strain rates. Processing maps representing low efficiency regions were observed at low temperature and high strain rate in both tensile and compressive deformation modes while the maximum efficiency regions depended on different deformation modes. Moreover, samples tested at stable processing conditions presented a smaller pore fraction than those at instable conditions that resulted in crack initiation during plastic deformation. This result shows that different deformation modes during plastic forming can affect formability changes of metallic alloys. Understanding of tension-compression behaviors will help us solve this problem.

• 한국정밀공학회지
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• 제26권3호
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• pp.73-80
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• 2009

In accordance with the trend for high-speed multi-axes, and the increasing technical sophistication of machine tools, thermal deformation has become an important factor in the accuracy of machine tools. It was analyzed that thermal deformation error accounts for about 70% of all errors made with machine tools. For precise temperature control, both cooling and heating should be implemented. A hot gas bypass type cooling cycle method has a simplified structure and temperature control accuracy to with in ${\pm}0.1^{\circ}C$. In this study, the performances of oil cooler system, including temperature controllability according to hot gas floe and preset temperature sustainability according to temperature load, were tested. It is expected that this study will contribute to the development and performances of oil cooler system, which could minimize thermal errors and improve the quality of precision machine tools.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 The 8th Asian Symposium on Precision Forging ASPF
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• pp.55-58
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• 2003

Many researches have been already done on the issues of high temperature deformation and the microstructural evolution. The information has been very useful for the plasticity industry, especially successful for the extrusion. However, the parts made with forging usually have a complex shape. It is difficult to control the distribution of the variables like strain, strain rate and temperature rise due to the working heat during a hot-forging process. Consequently, the microstructural variation could be occurred depending on the plastic deformation history that the forged part would get during a hot forging. In the present study, the microstructural characteristic of a hot-forged 6061 aluminum alloy has been discussed on the aspect of grain size evolution. A forging of 6061 aluminum alloy has been carried out for a complex shape with a dimensional variation. Also, finite element analysis has been done to understand how the deformation variables such as strain, strain rate give an influence on the microstructure of a hot forged aluminum product.

• 소성∙가공
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• 제23권7호
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• pp.425-430
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• 2014

The aim of the current study was to predict the plastic deformation behavior of a heated slab during hot rough rolling. FE-simulations were performed to investigate the metal flow and to locate the position of surface material from the slab through the rough rolling and onto the strip, using a material point tracking technique. In addition, experimental hot rolling trials were conducted where artificial defects were impressed onto a heated slab in order to validate the FE-simulation results. The simulated results show the same tendency of deformation behavior as the experimental measurements. The movement of slab defects from the side surface towards the strip center is directly linked to the extent of lateral spread during the rolling.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.23-26
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• 2003

This paper explains the die cooling method for improving tool life in the hot forging process. In continuous forming operation such as hot forging process, performed at high speeds, temperature increases of several hundred degrees may be involved. Die hardness was reduced due to thermal softening. Factor of die fracture are wear and plastic deformation of die due to hardness reduction by high temperature. Because die service life was reduced due to this phenomenon during hot forging, quantified data for optimal die cooling method is required. The new developed techniques for predicting tool life applied to estimate the production quantity for a spindle component and these techniques can be applied to improve the tool life in hot forging process

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 추계학술대회 논문집
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• pp.25-28
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• 2000

The flow stress of 304 stainless steel during high during hot forming process were determined by conducting hot compression tests at the range of 1273 K-1423 K and 0.05 /s-2.0 /s as these are typical temperature and strain rate in hot forging operation. Based on the observed phenomena, a constitutive model of flow stress was assumed as a function of strain, strain rate, temperature. Dynamic recrystallization was found to be the major softening mechanism with this conditions as previous studies. A finite element analysis was performed to predict the recrystallized volume fraction and the mean grain size in hot compression of 304 stainless steel.