• 한국항공우주학회지
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• 제33권2호
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• pp.60-66
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• 2005

부식은 기계류나 금속 부품의 성능과 수명을 저해하는 가장 큰 요인으로 작용하고 있다. 이 논문에서는 쇼트피닝이 부식환경하에서 Al 7075-T6의 피로수명에 미치는 쇼트피닝의 효과를 연구하였다. 쇼트피닝한 시험편의 피로한도는 약 52% 증가하는 것으로 나타났으며, 금속재 부품의 피로수명을 크게 연장시키는 것으로 보인다. 쇼트피닝을 한 시험편과 쇼트피닝 하지 않은 시험편을 1주에서 1년까지 비교 시험한 결과 부식은 피로강도를 현격히 감소시켰다. 쇼트피닝을 하였을 경우에는 부식에 의해 6개월 까지는 피로강도 및 피로수명이 감소하지 않은 것으로 나타났다. 따라서 쇼트피닝 가공이 금속재료의 수명에 대한 부식의 영향을 크게 감소시키는 효과가 있음을 알 수 있다.

• 한국생산제조학회지
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• 제6권4호
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• pp.80-88
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• 1997

An experimental investigation of the fatigue through crack growth behavior under simple stepped variable loading condition has been performed using Al7075-T651. Experiments were carried out by using cantilever bending type specimens, with chevron notches on a small electro-magnetic test machine. Tensile overloads have a retarding effect on the fatigue crack growth rates, therefore tensile overloads were used for the beneficial effect on the fatigue life. While in most cases compressive overloads have only a vanishing effect on crack growth rates, some experiments with single edge crack tension specimens reveal a marked growth retardation. The stress ratios used in this investigations varies from R=0.32 to 0.81, from R=0.04 to 0.76, from R=-0.15 to 0.73, and from R=-0.33 to 0.68 and the peak load for each case was not varied. The crack growth and crack closure were measured by Kikukawa's compliance method with a strain gauge mounted on the backside of each specimens. The results obtained are as follows. When the stepped variable load was applied, the smaller the stress ration was, the larger the delayed retardation of the crack growth rate was. The fatigue crack growh rate data obtained for through cracks were plotted well against the effective stress intensity factor range from 4.0 to 20.0MP{a^{SQRT}m}. It was found that the effective stress intensity factor range ratio was related well to the opening stress intensity factor, the maximum stress intensity factor, and crack length.

• 한국생산제조학회지
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• 제25권3호
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• pp.211-216
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• 2016

Al alloys are useful materials having high specific strength and are used in machining of parts having thin-walled structures for weight reduction in aircraft, automobiles, and portable devices. In machining of thin-walled structures, it is difficult to maintain dimensional accuracy because machining deformation occurs because of cutting forces and heat in the cutting zone. Thus, cutting conditions and methods need to be investigated and cutting signals need to be analyzed to diagnose and minimize machining deformation and thereby enhance machining quality. In this study, an investigation on cutting conditions to minimize machining deformation and an analysis on characteristics of cutting signals when machining deformation occurs are conducted. Cutting signals for the process are acquired by using an accelerometer and acoustic emission (AE) sensor. Signal characteristics according to the cutting conditions and the relation between machining deformation and cutting signals are analyzed.

• 한국생산제조학회지
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• 제25권4호
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• pp.253-257
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• 2016

The effects of re-peening on the compressive residual stress and fatigue life of Al7075-T6 were investigated. The compressive residual stress induced on the surface of components by shot peening is known to increase the fatigue life. However, the fatigue load relaxes the compressive residual stress of components. Re-peening is a technique to again induce the relaxed compressive residual stress and increase the total fatigue life of components. In this study, the re-peening process was applied to fatigue-loaded specimens. The compressive residual stress and fatigue life were examined for re-peened specimens with fatigue ratios of 30%, 50%, and 70%. The results showed that the compressive residual stress of the specimens was relaxed under the fatigue load. The re-peening process significantly increases the compressive residual stress and total fatigue life.

• 한국정밀공학회지
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• 제33권12호
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• pp.993-998
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• 2016

In today's manufacturing industries, the demand for light non-ferrous materials is considerable due to the need to improve productivity and manufacturability. Since the surface roughness of a material is important for improving the functionality of machined parts, various techniques for surface treatments have been developed to obtain non-ferrous materials with low roughness. A superfinishing method utilizing polishing films is generally applied to the anodized surface of Al7075 in order to improve its roughness. The objective of this research is to determine through experiment the parameters that facilitate the shortest processing time, using a superfinishing method, for reaching a roughness of Ra $0.2{\mu}m$. This objective is met by applying the Taguchi method in the experiments. Through the experiments of superfinishing, the effectiveness of the parameters adopted for the surface treatment is demonstrated.

• 대한금속재료학회지
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• 제50권9호
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• pp.669-675
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• 2012

Hot tearing was the most significant casting defect when the castability evaluation of the Al-Zn-Mg-Cu alloy system was conducted. It was related to the solidification range of the alloy. Therefore, the hot tear susceptibility of the AA7075 alloy, whose solidification range is the widest, was evaluated. The hot tear susceptibility was evaluated by using a mold for a hot tearing test designed to create the condition for the occurrence of hot tear in 8 steps. According to the tearing location and shape, a hot tear susceptibility index (HTS) score was measured. The solidification range of each alloy and hot tear susceptibility was compared and thereafter the microstructure of a near tear defect was observed. As a result, the HTS of the AA7075 alloy was found to be 67. Also, the HTS in relation to a change in Zn, Mg, Cu composition showed a difference of about 6-11% compared to the AA7075 alloy.

• 한국산업융합학회 논문집
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• 제26권5호
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• pp.743-750
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• 2023

Aluminum alloy is a material widely used in the aircraft industry. However, since it has relatively low hardness, strength and tribological properties, it is necessary to improve these properties. In this paper, a TiN thin film was coated on the surface of AL7075-T7351 using DC magnetron sputtering. The coating was performed by setting different deposition pressure, deposition time, and applied power. Then, the tribological properties of the thin film were investigated. As a result of the experiment, the hardness of the thin film was higher than that of the base material, and the specimen with the highest hardness had excellent friction coefficient, wear amount, and adhesive strength characteristics. Through this study, it was confirmed that the tribological characteristics of aluminum alloy can be improved by depositing thin films using DC magnetron sputtering.

• Composites Research
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• 제13권4호
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• pp.42-53
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• 2000

차세대 항공기소재로 관심을 가지고 있는 Al 7075/CFRP 적층 복합재인 CARALL(CARbon ALuminum Laminates)하이브리드 복합소재 제조를 위한 중요조건중의 하나인 Al 표면처리조건과 경화방법에 대해 조사하였다. 항공기용 Al 전처리 중 대표적인 것으로 증기탈지, 크롬산 양극산화 피막처리, 황산-중크롬산 나트륨 에칭처리 및 인산 양극산화 피막처리공정이 있다. 본 실험에서는 상기 전처리 공정을 모두 항공 규격에 준해서 실시하여 Lap shear 및 Bell peel strength를 비교함으로써 효과적인 접착강도를 나타내는 표면처리 공정을 찾아내고, 시편의 자연표면상태를 그대로 관찰할 수 있는 AFM(Atomic Force Microscope)장비를 이용하여 각 전처리 시편의 표면형상을 측정함으로써 표면형상과 접착강도와의 상관관계를 고찰 하였다. 그리고 Al 표면처리와 별도로 Al과 접착제 및 탄소섬유 프리프레그를 동시에 경화시키는 방법과 탄소섬유 프리프레그를 미리 경화시킨후 다시 Al과 탄소섬유 라미네이트를 접착필름을 이용하여 재 접착시키는 이차 경화법을 적용하여 상호 접착강도 및 물성을 비교하였다. 또한 이차경화법에서의 오토클레이브 압력 변화와 DMA(Dynamic Mechanical Analysis) 장비를 이용한 접착필름의 유리전이온도($T_g$) 측정을 통해 효과적인 공정압력 및 접착내구성 유지에 필요한 최소 경화시간을 파악하였다. 상기 결과로부터 정밀 치수관리가 필요하며 고접착강도, 내구성 항공기 부품을 제작하기 위한 알루미늄 표면처리 공정과 복합재 경화공정 조건을 제시하고자 하였다.

• 한국재료학회지
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• 제4권1호
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• pp.24-30
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• 1994

가공열처리한 7075Al합금을 $170^{\circ}C$에서 퇴화처리하여도 GP대는 완전히 분해되지 않았으며 초기의경도저하는 부분적인 GP대의 분해에 기인하고 $\mu '$의 생성으로 강도는 증가하다가 $\mu '$의 성장 및 $\mu$의 생성으로 강도는 다시 저하한다. 퇴화처리시 경도 곡선의 극소점이나 2차 피크점(극대점)에서 RRA처리한 시편의 응력부식 특성은 T6재에 비하여 상당히 개선되며 강도의 저하를 수반하지 않는다. 또한 저온인 $170^{\circ}C$에서 퇴화처리시 기지조직의 변화가 크지 않아 퇴화처리시 경도곡도의 극소점과 2차 피크점에서의 특성차이는 거의 없었다.

• 한국표면공학회지
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• 제39권5호
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• pp.235-239
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• 2006

The aluminum nitride(AlN) layer on Al7075 substrate has been formed through nitrogen ion implantation process. The implantation process was performed under the conditions : 100 keV energy, total ion dose up to $2{\times}10^{18}\;ions/cm^2$. XRD analysis showed that aluminum nitride layers were formed by nitrogen implantation. The formation of Aluminum nitride enhanced surface hardness up to 265HK(0.02 N) from 150HK(0.02 N) for the unimplanted specimen. Micro-Knoop hardness test showed that wear resistance was improved about 2 times for nitrogen implanted specimens above $5\;{\times}\;10^{17}\;ions/cm^2$. The friction coefficient was measured by Ball-on-disc type wear tester and was decreased to 1/3 with increasing total nitrogen ion dose up to $1\;{\times}\;10^{18}ions/cm^2$. The enhancement of mechanical properties was observed to be closely associated with AlN formation. AES analysis showed that the maximum concentration of nitrogen increased as ion dose increased until $5\;{\times}\;10^{17}\;ions/cm^2$.