• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2012.10a
• /
• pp.695-696
• /
• 2012

• Journal of Korea Foundry Society
• /
• v.41 no.6
• /
• pp.528-534
• /
• 2021

To confirm effects of natural and artificial aging of precipitate on thermal diffusivity and hardness, the studied Al-Mg-Si alloy were manufactured by gravity casting method with 0.6 wt% and 1.0 wt% additional Cu element. The samples were used for measuring thermal diffusivity and hardness. The addition of Cu, promoted by intermediates such as Q'' and θ'' phases, contributing to the improvement of hardness and high-temperature thermal diffusivity. The natural aging decreased the hardness of the Al-Mg-Si-Cu alloys with increasing time, but did not affect the thermal diffusivity.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.34 no.3
• /
• pp.220-225
• /
• 2014

Generally, the nonlinearity of ultrasonic waves is measured using a nonlinear parameter ${\beta}$, which is defined as the ratio of the second harmonic's magnitude to the power of the fundamental frequency component after the ultrasonic wave propagates through a material. Nonlinear parameter ${\beta}$ is recognized as an effective parameter for evaluating material degradation. In this paper, we evaluated the nonlinear parameter of Al6061-T6 which had been subjected to an artificial aging heat treatment. The measurement was using the transmitted signal obtained from contact-type transducers. After the ultrasonic test, a micro Vickers hardness test was conducted. From the result of the ultrasonic nonlinear parameter, the microstructural changes resulting from the heat treatment were estimated and the hardness test proved that these estimates were reasonable. Experimental results showed a correlation between the ultrasonic nonlinear parameter and microstructural changes produced by precipitation behavior in the material. These results suggest that the evaluation of mechanical properties using ultrasonic nonlinear parameter ${\beta}$ can be used to monitor variations in the mechanical hardness of aluminum alloys in response to an artificial aging heat-treatment.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.7
• /
• pp.717-722
• /
• 2011

The purpose of this study is to predict the residual stress in Al6061 during T6 heat treatment. In this study, the variable residual stress in case of the solid solution($530^{\circ}C$, 2h) and artificial ageing($175^{\circ}C$, 9h) of Al6061 subjected to T6 heat treatment is determined at different ageing times. A heat treatment experiment is conducted to determine the heat transfer coefficient, on the basis of which the residual stress during the T6 heat treatment is predicted. In order to take into account the relaxation of residual stress during artificial ageing, a Zener-Wert-Avrami function is used and elasto-plastic nonlinear analysis is conducted through FE-simulation. Further, the residual stress is measured by using the X-ray diffraction(XRD) method, and the result is compared with the result from the FE-simulation. It is found that the residual stress predicted form the FE-simulation is in good agreement with the residual stress measured by using the XRD method.

• Journal of Welding and Joining
• /
• v.12 no.1
• /
• pp.38-43
• /
• 1994

고강도 알루미늄합금은 중량이 가벼우면서 인장강도와 항복강도가 높고 가공성, 성형성이 좋아 항공기, 자동차, 선박 등 수송용 재료로 각광을 받고 있으며, 이 중 Al-Zn-Mg계(7000계) 알루미늄 합금은 용접 구조물용 경량소재로 활용범위가 높다. Al-Zn-Mg계 알루미늄 합금은 고온에서 용체화 처리후 저온으로 급냉시킨 재료를 자연시효 또는 인공시효처리를 하여 이 때 석출되는 시효 석출물에 의해 강도를 증가시킨 석출 경화형 합금이다. 그런데, 7000계열 알루미늄합금은 적절한 열처리 작업을 통해 최적의 기계적 성질이 얻어지도록 합금설계가 되어있기 때문에 구조물 제작시 용접에 의한 ARC 열을 받게 되면 열이력(thermal cycle)에 의해 모재의 미세조직이 변화하고 용접 결함이 발생하며 강도의 약화와 함께 내식성 등이 저하한다. 따라서 고강도 알루미늄합금의 용접성을 향상시키기 위해서는 용접부의 미세조직거동과 용접부에 발생하는 용접결함의 현상을 조사하여 용접용 고강도 합금에 필수적으로 요구되는 용접성에 대한 검토가 충분히 이루어져야 한다. 따라서 본 고에서는 알루미늄합금, 특히 7000계열 알루미늄합금에 주목하여, 용접방법, 각종 결함과 대책, 용접부의 시효경화와 응력부식균열 및 기계적 성질 등을 지금까지 보고된 각종 자료를 기초로 하여 3회에 걸쳐 기술하고자 한다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.5
• /
• pp.467-471
• /
• 2015

Thus far, solders used in electronics remain lead-based. Pb-free solutions in electronic components and systems are receiving increased attention in the semiconductor and electronics industries. Pb-free materials currently in used are Sn-37Pb, Sn-4Ag and Sn-4Ag-0.5Cu/Ni plate joints. In this study, solder alloys were used at high temperatures for artificial aging processing that was performed at $150^{\circ}C$ for 0hr, 100hr, 200hr, 400hr, 600hr and 1000hr. The SP test was conducted at $30^{\circ}C$ and $50^{\circ}C$. As a result, the maximum shear strength of all the specimens decreased with the increase in artificial aging time and temperature of the SP test. In addition, Pb-free solders showed higher total fracture energy compared with Sn-37Pb at high temperatures. The mechanical properties of Sn-4Ag-0.5Cu solder/Ni plate joints remained in excellent conditions in electronic parking systems at high temperatures.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.22 no.3
• /
• pp.90-96
• /
• 2014

The conventional SnPb solders were widely used for several decades in the electronic packing system due to the superior mechanical properties such as low melting point, better wettavility and good mechanical fatigue. However, in recent years, owing to adverse effect on the human health and environment, conventional SnPb solders have been replaced by Lead-free solders. In this research, the shear punch(SP) test of Sn-4Ag-(Cu)/Ni pad was performed. Pb-free solder alloys which are the environmentally friendly of the electronic components were performed at $150^{\circ}C$ for 100hr~1000hr to artificial aging processing. In order to evaluate the mechanical properties of solder joints, the SP test was conducted at $30^{\circ}C$ and $50^{\circ}C$. As a result, the maximum shear strength of almost the whole specimens was decreased with the increase in aging time and temperature of SP test. The mechanical properties of Sn-4Ag-0.5Cu solder were most excellent in all Pb-free solder which were produced by the SP test at $30^{\circ}C$.

• Journal of Power System Engineering
• /
• v.16 no.4
• /
• pp.66-73
• /
• 2012

본 연구는 횡방향 TIG 용접된 Al6013-T4 알루미늄 합금 용접부의 피로균열전파거동에 미치는 용접후열처리(PWHT)의 영향을 조사하는 것이 주목적이다. 기초적으로 인장시험, 경도 및 미세조직이 조사되었으며, 피로균열전파거동을 고찰하기 위한 피로 시험은 모두 중앙균열인장(CCT) 시험편에 대하여 수행되었다. T82열처리에 있어서 시효시간은 피로균열전파율, 인장강도 및 경도에 대단히 민감함을 나타내었으며, 모재와 열영향부재의 경우가 용접재보다 기계적 성질이 우수하였다. 횡방향 TIG 용접한 Al6013-T4 시험재의 용접후열처리 조건에 따라서 피로균열전파 저항에는 차이가 나타났으며, 본 실험의 조건하에서 24시간 인공시효 PWHT-82 시험편이 피로균열전파 저항이 가장 우수한 결과를 나타내었다.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.19 no.6
• /
• pp.411-419
• /
• 1999

It has been well recognized that a long term service at elevated temperature of $350^{\circ}C{\sim}550^{\circ}C$ induces embrittlement damage due to carbide precipitation and/or P, Sb and Sn segregation at grain boundaries and thereby deteriorates the grain boundary strength of heat resisting components in the energy-related plants. Therefore, it is very important to assess quantitatively the extent of embrittlement damage of heat resisting components to secure the reliable and efficient service condition and to prevent brittle failure in service. However, because fracture tests are limited in size and number of specimen obtained from the structural components, nondestructive test method is required. In this study, the optimum electrochemical parameters are investigated and discussed to evaluate nondestructive embrittlement damage for aged 2.25Cr-1Mo steels by means of electrochemical polarization test method (ECPTM) in proper corrosive environment. In addition, the electrochemical test results are compared with embrittlement degree evaluated by semi-nondestructive SP test.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2011.10a
• /
• pp.39.2-39.2
• /
• 2011

7075알루미늄 합금은 기계적 강도가 가장 높은 고강도 합금으로 열처리 공정이 반드시 필요하다. 그러나 열처리 공정 중 재료의 두께에 따른 내부 온도의 차이로 인한 잔류응력이 발생하여 최종 제품의 치수에 변화를 일으켜 제품 생산에 어려움이 있다. 따라서 본 연구에서 극저온 열처리 공정을 통하여 야기되는 7075알루미늄 합금의 기계적 특성 및 미세조직에 관하여 연구하였다. 7075 알루미늄 합금은 석출경화를 통한 강화가 이루어지며, 석출경화를 위해서 용체화 처리를 하여 인공시효를 하는 기존 공정과 비교하여 극저온 열처리 공정은 두 개의 추가적인 단계를 가지고 있다. 첫 번째 단계는 -196도의 액체 질소 속에 샘플을 극저온 ��칭을 하는 단계이고, 두 번째 단계는 샘플의 온도를 급격하게 올리는 up-hill quenching이다. 잔류응력은 X-ray diffraction을 이용한 $sin2{\psi}$ 방법으로 측정되었다. 극저온 열처리 후 기계적 특성을 평가하기 위하여 vickers hardness를 측정하였으며 미세 조직의 특성을 파악하기 위하여 EBSD와 TEM을 이용하여 평가하였다.