• Journal of Welding and Joining
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• 제18권2호
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• pp.213-213
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• 2000

This study was performed to investigate types and formation mechanism of cracks in two Al alloy welds, A5083 and A7NO1 spot-welded by pulse Nd: YAG laser, using SEM, EPMA and Micro-XRD. In the weld zone, three types of crack were observed: center line crack($C_{C}$), diagonal crack($C_{D}$), and U shape crack($C_{U}$). Also, HAZ crack($C_{H}$), was observed in the HAZ region, furthermore, mixing crack($C_{M}$), consisting of diagonal crack and HAZ crack was observed.White film was formed at the hot crack region in the fractured surface after it was immersed to 10%NaOH water. In the case of A5083 alloy, white films in C crack and $C_D crack region were composed of low melting phases, Fe₂Si$Al_8$ and eutectic phases, Mg₂Al₃ and Mg₂Si. Such films observed near HAZ crack were also consist of eutectic Mg₂Al₃. In the case of A7N01 alloy, eutectic phases of CuAl₂, $Mg_{32}$ (Al,Zn) ₃, MgZn₂, Al₂CuMg and Mg₂Si were observed in the whitely etched films near $C_{C}$ crack and $C_{D}$ crack regions. The formation of liquid films was due to the segregation of Mg, Si, Fe in the case of A5083 alloy and Zn, Mg, Cu, Si in the case of A7N01 aooly, respectively.The $C_{D}$ and $C_{C}$ cracks were regarded as a result of the occurrence of tensile strain during the welding process. The formation of $C_{M}$ crack is likely to be due to the presence of liquid film at the grain boundary near the fusion line in the base metal as well as in the weld fusion zone during solidification. The $C_{U}$ crack is considered a result of the collapsed keyhole through incomplete closure during rapid solidification. (Received October 7, 1999)

• Journal of Advanced Marine Engineering and Technology
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• 제23권3호
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• pp.360-368
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• 1999

The paper describes spectroscopic characteristics of plasma induced in the pulsed YAG laser welding of alloys containing a large amount of volatile elements. The authors have conducted the spectroscopic analyses of laser induced Al-Mg alloys plasma in the air and argon atmosphere. In the air environment the identified spectra were atomic lines of Al, Mg, Cr, Mn, Cu, Fe and Zn and singly ionized Mg lines as well as the intense molecular spectra of ALO and MgO formed by chemi-cal reactions of evaporated Al and Mg atoms from the pool surface with oxygen in the air. In argon atmosphere MgO and AlO spectra vanished but AlH spectrum was detected. the hydrogen source was presumable hydrogen dissolved in the base metals water absorbed on the surface oxide layer or $H_2$ and $H_2O$ in the shielding gas. The resonant lines of Al and Mg were strongly self-absorbed in particular self-absorption of the Mg line was predominant. These results show that the laser induced plasma was made of metallic vapor with relatively low temperature and high density.

• 한국분말재료학회지
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• 제11권1호
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• pp.69-73
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• 2004

The sintering characteristics of commercial 7xxx series Al-Zn-Mg-Cu alloy have been investigated. Sintering system of this blended elemental powder has aspects of both transient and supersolidus liquid phase sintering. Transient liquids occur when the constitution point during sintering lies in a solid phase region but where the sintering temperature is greater than either the melting point of one of the constituent or a eutectic temperature. Supersolidus liquid phase sintering occurs when a preblended powder is heated to a temperature between the solidus and liquids. However, these reaction were restrained their inter diffusion due to the appearance of the oxide film. Thus, 7xxx series Al alloy is extremely sensitive to process variables, including particle size, holding time and sintering temperature. Therefore, above phenomenons were observed formation and behaviour of the liquid by using SEM and DSC.

• 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.

• 마이크로전자및패키징학회지
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• 제25권2호
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• pp.9-17
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• 2018

Aluminum (Al) and its alloys have been used widely in a variety of industries such as structural, electronic, aerospace, and particularly automotive industries due to their lightweight characteristic, outstanding ductility, formability, high oxidation and corrosion resistance, and high thermal and electrical conductivity. Al have different kinds of alloys according to the various additional elements system and they should be selected properly depending on their effectiveness and suitability for their particular purpose. The major elements for Al alloys are silicon (Si), magnesium (Mg), manganese (Mn), copper (Cu), and zinc (Zn). In order for Al alloys to use for each industry, it is necessary to study of Al to Al joining and/or the Al to dissimilar materials joining to combine the individual parts into one. Many studies on joining technologies about Al to Al and Al to dissimilar materials have been performed such as press joining, bolted joint, welding, soldering, riveting, adhesive bonding, and brazing. This study reviews a variety of Al alloys and their joining method including its principles and properties with recent trends.

• 한국산업안전학회:학술대회논문집
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• 한국안전학회 1998년도 춘계 학술논문발표회 논문집
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• pp.57-62
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• 1998

구조물이나 기계요소내의 결함이 성장하여 파손(Failure)에 이르는 현상은 공학분야에서 중요하게 평가되어 오고 있다. 반복적으로 변하는 응력에 의하여 결함이 초기 성장을 거쳐 재료의 파손에 이르게 되는 과정인 피로파괴는 파괴역학의 한 중요한 분야이다. 이에, 본 연구에서는 열처리의 특성상 부식환경에 매우 민감한 Al-Zn-Mg-Cu Alloy 7075에 대하여 Peak Aged T65l Tempering을 실시한 Al-Alloy 7075-T65l에 대하여 각기 환경(대기, 물, 해수)의 변화가 부식피로균열성장에 미치는 영향과 부식환경에서의 긴 균열(Long Crack)과 짧은 균열(Short Clark)의 부식피로균열 성장특성을 비교, 고찰하여 초기균열의 잠재시간과 안정성장 시간을 예측하여 구조물의 수명예측 및 안전성 평가에 기여 할 수 있는데 목적이 있다. (중략)

• 한국재료학회지
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• 제9권6호
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• pp.609-614
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• 1999

The effect of the amount of $SiO_2$dopant on the behavior of $AlO_2$$O_3$-composite formation by melt oxdation of Al-alloy was examined in this paper. The $SiO_2$powder was spread on the top surface of the Al-1Mg-3-Si-5Zn-1Cu alloy in th alumina crucible. The selected amount of each powder was 0.03, 0.10, 0.16g/$\textrm{cm}^2$. The oxidation behavior was determined by observing the weight gain after the heat treatment for 10 hours at 1373K. The macroscopic structure of formed oxide layer was examined by an optical microscope. The top surface and the cross-section of the grown oxide layer were investigated by SEM and analysed by EDX. The $SiO_2$ powder was determined to enhance oxidation by thermit reaction with Al which reduced the growth incubation period of the oxidation layer. As the amount of the $SiO_2$dopant increased, the growth rate decreased due to the precipitated Si which blocked the Al-alloy channel in the composite materials. However, more uniform layer was obtained due to the occurrance of the enhanced oxidation reaction in the whole alloy surface compared to the case of addition of less amount of dopant.

• 한국재료학회지
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• 제28권9호
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• pp.534-538
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• 2018

The annealing characteristics of a cold rolled Al-6.5Mg-1.5Zn alloy newly designed as an automobile material is investigated in detail. The aluminum alloy in the ingot state is cut to a thickness of 4 mm, a total width of 30 mm and a length of 100 mm and then reduced to a thickness of 1 mm (reduction of 75 %) by multi-pass rolling at room temperature. Annealing after rolling is performed at temperatures ranging from 200 to $400^{\circ}C$ for 1 hour. The tensile strength of the annealed material tends to decrease with the annealing temperature and shows a maximum tensile strength of 482MPa in the material annealed at $200^{\circ}C$. The tensile elongation of the annealed material increases with the annealing temperature, while the tensile strength does not, and reaches a maximum value of 26 % at the $350^{\circ}C$ annealed material. For the microstructure, recovery and recrystallization actively occur as the annealing temperature increases. The recrystallization begins to occur at $300^{\circ}C$ and is completed at $350^{\circ}C$, which results in the formation of a fine grained structure. After the rolling, the rolling texture of {112}<111>(Cu-Orientation) develops, but after the annealing a specific texture does not develop.

• 한국주조공학회지
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• 제38권6호
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• pp.111-120
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• 2018

In this study, the effects of two different casting methods (gravity casting and, diecasting) and various solid-solution conditions on the mechanical properties of ASC (Al-10.5wt%Si-1.75wt%Cu) and ALDC12 (Al-10.3wt%Si-1.72wt%Cu-0.76wt%Fe-0.28wt% Mn-0.32wt%Mg-0.9wt%Zn) alloys were investigated. A thermodynamic solidification analysis program (PANDAT) was used to predict the liquidus, solidus, and phases of the used alloys. In the results of an XRD analysis, ${\beta}$-AlFeSi peaks were observed only in the ALDC12 alloy regardless of the casting method or SST (solid-solution treatment) conditions. However, according to the results of a FE-SEM observation, both ${\theta}(Al_2Cu)$ and ${\beta}$-AlFeSi were found to exist besides ${\alpha}$-Al and eutectic Si in the gravity-casted ASC alloy at $500^{\circ}C$ after a SST of 120min. The ${\alpha}$-AlFeSi and ${\beta}$-AlFeSi phases including the eutectic phases were also found to exist in the ALDC12 alloy. The results of a microstructural observation and analyses by XRD, FE-SEM and EDS were in good agreement with the PANDAT results. The gravity-casted ALDC12 and ASC specimens showed the highest Y.S. and UTS values after aging for three hours at $180^{\circ}C$ after a SST at $500^{\circ}C$ for 30min. At longer solid-solution treatment times at $500^{\circ}C$ in the gravity-casted ALDC12 and ASC specimens, the elongations of the ASC alloys increased, whereas they decreased slightly in the ALDC12 alloys.

• 한국주조공학회지
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• 제32권2호
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• pp.98-103
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• 2012

Recently, development of Al-based alloys for high mechanical performance has been an important issue in automotive industry. The present study focused on the design of a high strength Al-based alloy for rheo-diecasting. The research was based on thermodynamic calculation and experimentals to optimize the alloy compositions. Two important considerations were carried out: i) to obtain uniform slurry with fine and globular microstructures for rheo-diecasting, ii) to be strengthend by T6 heat treatment. In order to evaluate the effect of Si content on the slurry microstructure and castability, thermodynamic calculation and fluidity test were carried out. The effects of various alloying components, such as Mg, Cu and Zn, on age hardenability were also investigated. The mechanical properties of the rheo-diecasting products using the newly developed alloy are 324MPa in tensile strength, 289MPa in yield strength, and 11.2% in elongation after T6 heat treatment.