• 한국주조공학회지
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• 제34권1호
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• pp.22-26
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• 2014

Internal defects, such as shrinkage during casting, cause stress concentrations and initiate cracking. Therefore, it is important to understand the effects of internal defects on the mechanical properties including the impact behavior. This study evaluates the effects of internal casting defects on the impact performance of A356 Al-alloy castings. The internal shrinkage defects in the casting impact specimen are scanned using an industrial Computed Tomography (CT) scanner, and drop impact tests are performed with varing impact velocities on the A356 casting aluminium specimen ($10mm{\times}10mm$ section area) in order to locate the fracture energy under an impact load. The specimens with defects with a diameter less than 0.35 mm exhibit equivalent fracture impact energies of approximately 32 J and those with a 1.7 mm diameter defect reduced the fracture impact energy by 35%.

• 한국주조공학회지
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• 제20권4호
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• pp.269-276
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• 2000

So far, the study on semi-solid process has been carried out to develop and research new advanced materials without some casting defects. In this study, A356 billets consisted of various dendritic shapes were prepared using electro-magnetic stirring process continuously. As-cast respectively has liquidus temperature of $625.6^{\circ}C$ and solidus temperature of $573.55^{\circ}C$ A356 slugs were reheated homogeneously at different temperatures of 580, 590 and $605^{\circ}C$, followed by squeezing in a mold insulated with applied pressures(0, 25, 50 and 70 MPa). In order to investigate on aging responce for casts, 50 MPa squeezed specimen among all specimens was prepared in aging treatments, which conditions are aging temperature of $160^{\circ}C$ and holding times of 0, 45, 90, 270, 360, 720, 1440 and 2880 min after solution treatment ($540^{\circ}C$ for 10 hr). SSM ingot with the output velocity of 150mm/min appeared more spheroidal shape and fine structure than that with the output velocity of 250 mm/min. According to increasing in reheating temperature, numbers of fatigue cycles, U.T.S and elongation increased at same time.

• 소성∙가공
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• 제18권4호
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• pp.296-303
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• 2009

The effect of porosity on the high-cycle fatigue properties of Al-Si-Mg casting aluminum alloys was investigated in this study. Microstructure examination, tensile and high-cycle fatigue test were conducted on both Al-Si-Mg casted (F) and heat-treated (T6) conditions. Porosity characteristics on the fracture surfaces of fatigue-tested samples were examined using SEM and image analysis. The microstructure observation results showed that eutectic Si particles were homogeneously dispersed in the matrix of the Al-Si-Mg casting alloys, but there were porosities formed as cast defects. The high-cycle fatigue results indicated that the fatigue strength of the 356-T6 alloy was higher than that of the 356-F alloys because of the significant reduction in volume fraction of pores by heat treatment. The SEM fractography results showed that porosity affected detrimental effect on the fatigue life: 80% of all tested samples fractured as a result of porosity which acted as the main crack initiation site. It was found that fatigue life decreased as the size of the surface pore increased. A comparison was made between surface pore and inner pore for its effect on the fatigue behavior. The results showed that the fatigue strength with the inner pores was higher than that of the surface pore.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.350-352
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• 2009

The effect of porosity on the high-cycle fatigue properties of Al-Si-Mg casting aluminum alloys was investigated in this study. Microstructure examination, tensile and high-cycle fatigue test were conducted on both Al-Si-Mg casted (F) and heat-treated (T6) conditions. Porosity characteristics on the fracture surfaces of fatigue-tested samples were examined using SEM and image analysis. The microstructure observation results showed that eutectic Si particles were homogeneously dispersed in the matrix of the Al-Si-Mg casting alloys, but there were porosities formed as cast defects. The high-cycle fatigue results indicated that the fatigue strength of the 356-T6 alloy was higher than that of the 356-F alloys because of the significant reduction in volume fraction of pores by heat treatment. The SEM fractography results showed that porosity affected detrimental effect on the fatigue life: 80% of all tested samples fractured as a result of porosity which acted as the main crack initiation site. It was found that fatigue life decreased as the size of the surface pore increased. A comparison was made between surface pore and inner pore fur its effect on the fatigue behavior. The results showed that the fatigue strength with the inner pores was higher than that of the surface pore.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.299-302
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• 2005

Semisolid A356 slurries were prepared by electromagnetic stirring casting and by inoculation of Al-5Ti-B master alloy. As stirring time and addition of Al-5Ti-B are different, the grain size of the primary phase is different. Through the experiment of rheocast in a Buhler horizontal die casting machine, it was found that the finer the equiaxed primary dendrites, the smoother the die filling and better cast quality. Small equiaxed primary dendrite also results in less liquid segregation on the surface.

• 대한기계학회논문집A
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• 제34권9호
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• pp.1257-1263
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• 2010

함정구조물은 함내 엔진 및 프로펠러 추진력의 환경진동에 노출되어 있다. 일반적으로 함상구조물은 함상진동규격인 MIL-STD-167-1A 에 따라 개발되고 있으며, 장기간 사용을 목적으로 하는 함상구조물의 진동에 대한 피로수명은 해석적 접근법과 진동실험을 통해 반드시 평가되야 한다. 본 논문에서는 함상구조재로 사용된 주조 알루미늄합금인 A356 의 피로강도를 14 S-N 법으로 평가하고, 구조물의 작용응력은 함상진동규격에 준하는 주파수응답해석을 통해 분석되었다. 최대등가응력의 주파수는 최대실험주파수에서 나타났으며, 함상장비의 진동피로수명은 누적손상법에 의해 평가되었다.

• 한국주조공학회지
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• 제22권3호
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• pp.109-113
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• 2002

A good fluidity of high strength Al-alloys is required to cast thin wall castings needed to reduce the weight of cast parts. The fluidity, measured as the length to which the metal flows in a standard channel, is affected by many factors, such as the pouring temperature, solidification type of the alloy, the channel thickness, melt head, mold materials and temperature, coating etc. Therefore the experimentally measured fluidity scatters very much and makes it difficult to estimate the fluidity of a melt with a few measurements. The effect of Ti content and grain refinement on the fluidity of high strength aluminum alloy was investigated with a test casting with 8 thin flow channels to reduce the scattering of the fluidity results. The fluidity of Al-4.8%Cu-0.6%Mn Al-6.2%Zn-1.6%Mg-1.0%Cu and well-known commercial aluminum alloy, A356 was tested. Initial content of Ti was varied from 0 to 0.2wt% and Al-5Ti-B master alloy was added for grain refinement. The flow length varied linearly with superheat. By adding Ti and Al-5Ti-B, the fluidity increased. The grain size decreased by adding grain refiner at the same time. The fluidity depended on the degree of grain refinement. The fluidity of the alloy solidifying in mushy type is improved by grain refinement, because grain refinement increases the solid fraction at the time of flow stoppage.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.350-353
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• 2005

Microstructures according to experimental conditions (pouring temperature, stirring current and stirring time) and hardness according to aging time were investigated for A356 cast aluminum alloy and 7075 wrought aluminum alloy. In pouring temperature control, grains became larger and non-uniform at high temperature, however dendritic shapes were shown at lower temperature. In stirring current control, dendritic grains were not destroyed enough at lower current, however fine grains were agglomerated at higher current. And, in stirring time control, grains were more globular but grew larger and larger with the stirring time increasing.

• 한국주조공학회지
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• 제32권1호
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• pp.24-31
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• 2012

In this study, semi-solid thin plate of A 356 aluminum alloy was fabricated by using slope plate apparatus and vacuum pressurization. Slope plate was used to produce semi-solid material with spheroidal microstructures. After molten metal was poured into the slope plate connected to the pouring hole of die, semi-solid material flowed into the die cavity by vacuum degree. The primary crystals of the cast metal became spheroidal. In order to increase the working pressure, gas pressurization of U shape was designed for fabrication of thin plate. For 3 bar of gas pressure and 60 mmHg of vacuum degree, thin plate was fabricated without defects on surface.

• 한국추진공학회지
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• 제16권5호
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• pp.81-88
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• 2012

액체로켓엔진의 핵심부품인 터보펌프의 경량화를 위하여 케이싱에 알루미늄 합금 소재를 도입하였고 생산성 향상 및 생산 단가의 절감을 위하여 주조 공법을 도입하였다. 부품의 신뢰도가 생명인 액체로 켓엔진에 주조를 사용하기 위하여 올바른 주조 규격 수립 및 주조 공법의 최적화, 그리고 주조된 제품의 다방면에 걸친 철저한 검증을 실시하는 것이 필수적이다. 이번 연구에서는 알루미늄 합금인 A356.0-T6 합금을 이용하여 연료펌프 입구케이싱을 주조하였으며 주조 품질의 기본적인 구조 검증을 위하여 파열시험을 수행하였다. 주조된 형상에 맞추어 구조해석을 실시하여 파열 시점을 예측하였으며 파열시험 시 제품에 부착된 스트레인게이지를 이용하여 해석을 통한 변형률 예측과 비교하였다.