• 한국재료학회지
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• 제31권6호
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• pp.339-344
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• 2021

Composite materials offer distinct and unique properties that are not naturally inherited in the individual materials that make them. One of the most attractive composites to manufacture is the aluminum alloy matrix composite, because it usually combines easiness of availability, light weight, strength, and other favorable properties. In the current work, Powder Metallurgy Method (PMM) is used to prepare Al2024 matrix composites reinforced with different mixing ratios of yttrium oxide (Y₂O₃) particles. The tests performed on the composites include physical, mechanical, and tribological, as well as microstructure analysis via optical microscope. The results show that the experimental density slightly decreases while the porosity increases when the reinforcement ratio increases within the selected range of 0 ~ 20 wt%. Besides this, the yield strength, tensile strength, and Vickers hardness increase up to a 10 wt% Y₂O₃ ratio, after which they decline. Moreover, the wear results show that the composite follows the same paradigm for strength and hardness. It is concluded that this composite is ideal for application when higher strength is required from aluminum composites, as well as lighter weight up to certain values of Y₂O₃ ratio.

• 대한기계학회논문집A
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• 제36권12호
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• pp.1577-1583
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• 2012

횡방향 관통 효율 강화 탄체(PELE)는 기폭장치가 없는 새로운 개념의 발사체이다. PELE 는 배면이 닫혀있는 고밀도 피복과 저밀도 충전재로 구성되어있다. PELE 의 폭발 특성을 연구하기 위해 AUTODYN-3D code 를 이용하여 발사체와 표적체의 모델을 구축하였다. PELE 의 의해 알루미늄-2024 합금 표적체를 천공하는 과정을 시뮬레이션으로 구현하였으며 또한 다양한 내부 충전재에 의해 분산되는 표적체의 파편 특성도 연구하였다. PELE 파편의 유한요소해석은 AUTODYN-3D code 의 추계학적 파괴기준을 사용하여 구현되었다. 내부 충전재의 팽창으로 인해 파편은 속도를 얻으며 횡방향으로 분산된다. 따라서 손상영역의 범위가 증강한다. 관통 및 횡방향 분산 과정에서 생성되는 파편은 내부 충전재의 충격 압력에 따라 그 양과 형태가 다른 것으로 나타났다.

• 한국자동차공학회논문집
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• 제20권1호
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• pp.141-146
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• 2012

Aluminum alloys have been used with various thicknesses suitable for light weight of structure. It is known that the thickness effect of material is an important factor affecting fatigue crack propagation under constant fatigue stress condition. In this work, we presented the behavior of fatigue crack propagation in thin plate compared to thick plate Al 2024-T3 alloy with referred thickness effect in a correlative equation determined by the shape factor and the loading factor. We chose two factors that are used in the correlative equation with considering that the experiments were carried out under a constant fatigue stress condition. The thickness ratio of thin plate compared to thick plate and the equivalent effective stress intensity factor ratio depending on thickness were chosen as shape and loading factors. A correlative equation is utilized to determine the equivalent effective stress intensity factor range of thin plate and identify the degree of increasing phenomenon of fatigue life in thin plate compared to thick plate.

• 한국해양공학회지
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• 제7권1호
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• pp.124-132
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• 1993

In order to examine the effect of anisotropy and stress ratio on fatigue crack propagation rate and opening-closing behavior and also arrest behavior by single tension peak overload, the fatigue tests of constant amplitude atress and single tension peak overload adding to cycle of constant amplitude were carried out in stress ratio of -0.4, -0.2, and 0.4 with materials of T-L and L-T directions in 2024-T3 aluminum alloy plate. Crack opening-closing begavior were measured by the compliance method using COD gage and strain gage. In case of the crack opening-closing behavior was measured by strain gage, the effect of stress ratio is unchangeable. But in the case of COD gage, that is remarkably decreased. Fictitious effective stress intensity factor(U sub(f)) and effective stress intensity factor ratio(U) in L-T direction was higher than those in T-L direction and also threshold arrest overload ratio incrased as stress ratio decreased and that of T-L direction was higher than that in L-T direction.

• 열처리공학회지
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• 제37권3호
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• pp.121-127
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• 2024

We investigate the effect of T6 heat treatment on the microstructure and mechanical properties of AA365 (Al-10.3Si-0.37Mg-0.6Mn-0.11Fe, wt.%) alloy fabricated by vacuum-assisted high pressure die casting by means of thermodynamic calculation, X-ray diffraction, scanning and transmission electron microscopy, and tensile tests. The as-cast alloy consists of primary Al (with dendrite arm spacing of 10~15 ㎛), needle-like eutectic Si, and blocky α-AlFeMnSi phases. The solution treatment at 490 ℃ induces the spheroidization of eutectic Si and increase in the fraction of eutectic Si and α-AlFeMnSi phases. While as-cast alloy does not contain nano-sized precipitates, the T6-treated alloy contains fine β' and β' precipitates less than 20 nm that formed during aging at 190℃. T6 heat treatment improves the yield strength from 165 to 186 MPa due to the strengthening effect of β' and β' precipitates. However, the β' and β' precipitates reduce the strain hardening rate and accelerate the necking phenomenon, degrading the tensile strength (from 290 to 244 MPa) and fracture elongation (from 6.6 to 5.0%). Fractography reveals that the coarse α-AlFeMnSi and eutectic Si phases act as crack sites in both the as-cast and T6 treated alloys.

• 한국재료학회지
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• 제28권12호
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• pp.738-747
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• 2018

For the aerospace structural application of high-strength 2xxx series aluminum alloys, stress corrosion cracking(SCC) behavior in aggressive environments needs to be well understood. In this study, the SCC sensitivities of 2024-T62, 2124-T851 and 2050-T84 alloys in a 3.5 % NaCl solution are measured using a constant load testing method without polarization and a slow strain rate test(SSRT) method at a strain rate of 10-6 /sec under a cathodic applied potential. When the specimens are exposed to a 3.5 % NaCl solution under a constant load for 10 days, the decrease in tensile ductility is negligible for 2124-T851 and 2050-T84 specimens, proving that T8 heat treatment is beneficial in improving the SCC resistance of 2xxx series aluminum alloys. The specimens are also susceptible to SCC in a hydrogen-generating environment at a slow strain rate of $10^{-6}/sec$ in a 3.5 % NaCl solution under a cathodic applied potential. Regardless of the test method, low impurity 2124-T851 and high Cu/Mg ratio 2050-T84 alloys are found to have relatively lower SCC sensitivity than 2024-T62. The SCC behavior of 2xxx series aluminum alloys in the 3.5 % NaCl solution is discussed based on fractographic and micrographic observations.

• 한국주조공학회지
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• 제44권2호
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• pp.43-48
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• 2024

• 한국항공우주학회지
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• 제38권4호
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• pp.382-388
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• 2010

본 논문에서는 마그네슘합금 재료로 제작된 F-5E/F의 외부 연료탱크 수평 핀의 균열 발생 원인을 분석하고 적절한 대체 재질을 검토하여 탱크의 투하 안전성을 보장하도록 핀의 형상을 재설계하였다. 재료는 재료의 성질과 조달 용이성을 고려하여 강도 및 파괴 인성이 기존재료보다 강하지만 핀 1개당 65%의 무게증가가 예상되는 알루미늄 합금 2024-T351을 선택하였다. 핀의 무게 증가로 인한 연료탱크 무게 중심의 후방 이동을 허용한계 이내로 유지하기 위하여 크기를 20% 축소하고, 두께 7 mm, 곡률 반경 8.5 mm로 설계된 핀에 대하여 정적 및 동적 응력을 해석한 결과 후방 체결부 및 체결 홀의 안전계수가 증가되었음이 확인되었다.

• 한국생산제조학회지
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• 제19권1호
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• pp.108-113
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• 2010

Decreasing products lifecycles and increasing consumers desires for quality and design make the automotive industries try to reduce time for developing new designs. In order to reduce developing time, I have designed head lamps, which are really important to have an effect on brand identities and images, using layers concept that is one of the international automotive design trends by alias and photoshop, and produced prototype by RP. To assemble the produced prototype to the body and manufacture the frame to exterior modelling efficiently, I have studied on joining dissimilar materials of aluminum alloy that can make the prototype lighter and stainless steel, which is good for corrosion resistance by using laser beam. These materials were welded for finding the optimum joining condition and evaluating the soundness of joining zone. The joining was performed under the condition of laser power 500, 550, 575, 600W and 11~14Hz. In this study, the suitable joining condition between aluminum alloy (Al 2024) and stainless steel (STS 304) can be obtained at the laser power 575W and frequency 12Hz.

• 한국항공운항학회지
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• 제27권3호
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• pp.24-29
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• 2019

The paste-type adhesive can be stored for a certain period of time and can be cured at room temperature. So it is mainly used for crack patching repair of aircraft airframe structures. This study analysed the influence of environmental factors and evaluated the adherence strength characteristics according to the adherence delay time of the paste-type adhesive. The test specimens were made of aluminum alloy(AL 2024-T3) with reference to ASTM D1002 which is generally performed to measure the adherence strength of the adhesive used for metal bonding. As a result of analysing the influence of temperature and humidity, it was found that the optimal temperature range is $24.5{\pm}0.5^{\circ}C$ and the optimal humidity range is $71{\pm}1%$ for maintenance work of the aircraft using EA-9320 adhesive. In addition, the adherence strength did not decrease with the inherent application time of the EA-9320, but it was found that the adherence strength dropped rapidly when the applied time exceeded the inherent application time of it.