• Journal of Welding and Joining
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• v.22 no.5
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• pp.65-72
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• 2004

The tendency and degree of hot cracking of high strength 5083, 6N01 and 7N01 Al alloy welds by using DCSP-GTAW through modified Varestraint test and autogenous butt welding were investigated. In hot cracking test, 6N01 alloy showed the highest susceptibility to hot cracking in the weld metal and HAZ. Cracking susceptibilities generally increased with increase of solidification temperature range of the base metal and bead penetration-to-width ratio of the weld metal. The cracks in welds of the alloys vertically formed to solid-liquid interface and propagated along with columnar grain boundaries. The fracture facets of cracks showed the typical morphology of solidification crack observed as dendritic structures. Especially, in 6N01 alloy, liquation cracks which were due to elements of Si, Fe and Mg also observed in HAZ near fusion boundary. In butt welding of different Al alloys, the bead crack was mainly occurred in the welds of 6N01, 7N01 and other Al alloys together with 6N01 or 7N01. In the butt welds of 7N01, it was found that the component of Cu had an effect on the higher susceptibility to the hot cracking.

• Journal of Digital Contents Society
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• v.18 no.7
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• pp.1387-1391
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• 2017

Cutting power estimation can be used to select appropriate actuators in the design process of machine tools. Therefore, accurate estimation of cutting power is an important part of the design process. In this study, pipe cutting power is first calculated theoretically using the slotting cutting power equation and then verified experimentally. In this case, a pipe cutting machine is used to cut two pipes made of different materials. Power consumptions in the motor during pipe cutting are measured by using the embedded software, Labview, and NI hardware. The slotting cutting power equation can thus be confirmed easily comparing theoretically calculated cutting powers with experimentally measured cutting powers. The pipe materials used in this study are SUS304 and AL6N01. The specific cutting power of AL6N01 material is proposed through our cutting experiment. As a result, this cutting power can be used to design machining tools for AL6N01 material.

• Journal of Welding and Joining
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• v.21 no.5
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• pp.540-546
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• 2003

Recently Al alloys are being used gradually for structural materials of transports. In welding of Al alloys used for transports, good weldabilities as well as adequate mechanical properties of the welds should be ensured as structural materials. In this study, the welds formation, macro and microstructural characteristics, generation of defects and hardness distribution in welds of Al alloys of 5083, 6N01 and 7N01 by DCSP- and AC-GTA welding process, were investigated. The deeper penetration was obtained in all welds of the alloys by DCSP-GTAW with He gas, compared with those by using AC-GTAW. The 6N01 alloy showed high susceptibilities to solidification cracking in weld metal and liquation cracking in HAZ of the welding beads of both DCSP- and AC-GTAW process. The cracking ratio of 6N01 alloy was increased with increasing of welding current. The porosity ratios in weld metal of all alloys used were extremely low including all welding conditions of DCSP-GTAW. However, in AC-GTAW process, the porosity ratios of the welds using Ar gas showed much higher values than those using He gas.

• Electronic Materials Letters
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• v.14 no.6
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• pp.784-792
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• 2018

In this letter, a standard deviation based optimization technique has been applied on High Resolution X-ray Diffraction symmetric and asymmetric scan results to accurately determine the Aluminum molar fraction and lattice relaxation of Molecular Beam Epitaxy grown compositionally graded Aluminum Gallium Nitride (AlGaN)/Aluminum Nitride/Gallium Nitride (GaN) heterostructures. Mathews-Blakeslee critical thickness model has been applied in an alternative way to determine the partially relaxed AlGaN epilayer thicknesses. The coupling coefficient determination has been presented in a different perspective involving sample tilt method by off set between the asymmetric planes of GaN and AlGaN. Sample tilt is further increased to determine mosaic tilt ranging between $0.01^{\circ}$ and $0.1^{\circ}$.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.4
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• pp.268-273
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• 1998

Effect of aging treatment on the microstructures and mechanical properties of 6N01 Aluminium alloy was investigated by differential scanning calorimetry, transmission electron microscopy, microhardness measurement and tensile test. It was found that the precipitation sequence of 6N01 Aluminium alloy was GP zone ${\rightarrow}$ metastable hexagonal $Mg_2S_i({\beta}^{\prime})$,${\rightarrow}$ equilibrium fcc $Mg_2S_i({\beta})$, and the precipitates at peak aged condition were GP zones and ${\beta}^{\prime}$ phase. Microhardness changes during over aged condition showed very small decrease upon increased aging time. This result was attributed to the very slow transformation rate of ${\beta}^{\prime}$ to ${\beta}$. Maximum hardness(116 Hv) and tensile strength(312.6MPa) with 22.3% elongation were obtained from the specimen aged at $180^{\circ}C$ for 15hrs.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1996.11a
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• pp.6-6
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• 1996

Ceramic based nanocomposite, in which nano-sized ceramics and metals were dispersed within matrix grains and/or at grain boundaries, were successfully fabricated in the ceramic/cerarnic and ceramic/metal composite systems such as $Al_2O_3$/SiC, $Al_2O_3$/$Si_3N_4$, MgO/SiC, mullite/SiC, $Si_3N_4/SiC, $Si_3N_4$/B, $Al_2O_3$/W, $Al_2O_3$/Mo, $Al_2O_3$/Ni and $ZrO_2$/Mo systems. In these systems, the ceramiclceramic composites were fabricated from homogeneously mixed powders, powders with thin coatings of the second phases and amorphous precursor composite powders by usual powder metallurgical methods. The ceramiclmetal nanocomposites were prepared by combination of H2 reduction of metal oxides in the early stage of sinterings and usual powder metallurgical processes. The transmission electron microscopic observation for the $Al_2O_3$/SiC nanocomposite indicated that the second phases less than 70nm were mainly located within matrix grains and the larger particles were dispersed at the grain boundaries. The similar observation was also identified for other cerarnic/ceramic and ceramiclmetal nanocornposites. The striking findings in these nanocomposites were that mechanical properties were significantly improved by the nano-sized dispersion from 5 to 10 vol% even at high temperatures. For example, the improvement in hcture strength by 2 to 5 times and in creep resistance by 2 to 4 orders was observed not only for the ceramidceramic nanocomposites but also for the ceramiclmetal nanocomposites with only 5~01%se cond phase. The newly developed silicon nitride/boron nitride nanocomposites, in which nano-sized hexagonal BN particulates with low Young's modulus and fracture strength were dispersed mainly within matrix grains, gave also the strong improvement in fracture strength and thermal shock fracture resistance. In presentation, the process-rnicro/nanostructure-properties relationship will be presented in detail. The special emphasis will be placed on the understanding of the roles of nano-sized dispersions on mechanical properties.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.4 s.346
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• pp.1-7
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• 2006

AlN thin films have been fabricated by using RF magnetron sputtering method and their crystal orientations, microstructures and piezoelectric properties have been investigated with variation of the $Ar/N_2$ gas ratio and the substrate temperature. Particularly, when the $Ar/N_2$ gas ratio and the substrate temperature are 10/10 (sccm) and $400^{\circ}C$, respectively, the AlN thin film exhibits the highest (002) orientation. The result of the surface roughness measurement by using AFM shows that the surface roughness becomes better as the partial pressure of $N_2$ increases at the substrate temperature of $400^{\circ}C$ and it becomes the smallest value of 2.1 nm when $Ar/N_2$ is 0/20 (sccm). The AFM measurement also shows that when $Ar/N_2$ is 10/10 (sccm) shows that surface roughness becomes better as the substrate temperature increases from room temperature up to $300^{\circ}C$ and then it becomes worse as the substrate temperature goes up from $300^{\circ}C$. At the substrate temperature of $300^{\circ}C$ and $Ar/N_2$=10/10 (sccm), the surface roughness is 3.036 nm. The piezoelectric constant ($d_{33}$) of AlN thin film is measured by Pneumatic probe method. The measurement shows that the AlN thin film with the highest (002) orientation, fabricated at $Ar/N_2$=10/10 (sccm) and the substrate temperature of $400^{\circ}C$, has the best Piezoelectric constant ($d_{33}$) of 6.01 pC/N.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.108-116
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• 1991

In the non-linear behavior of many materials, there is difference between the monotonic behavior by static load and the cyclic behavior by cyclic load. In particular, the short fatigue cracks to propagate in elasto-plastic stress concentrations(notches), are governed significantly by the cyclic behavior of materials. Accordingly, it is needed to investigate and compare the monotonic and cyclic behavior of materials. In the pressent study, the stress-strain relations of materials by monotonic and cyclic load tests were examined for 2 kinds of steels(SS41, HT80) and 5 kinds of Al-alloys(A5083-O, A6N01-T5, A7N01-T4, A7016-T6, A7178-T6). And the constants for mechanical properties of the materials were determined by experimental results, Moreover, when a notch was subjected to cyclic load, the effect of cyclic hardening property of materials on the variation of stress-strain amplitude in the notch tip was discussed by the application of Neuber's rule and experiments for a center notched plate.

• The Korean Journal of Nuclear Medicine
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• v.37 no.2
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• pp.94-102
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• 2003

Purpose : Cerebral blood flow (CBF) reactivity to acetazolamide (ACZ) is useful to select patients with hemodynamic failure. However, it is still a matter of speculation that varying degrees of regional CBF increases after ACZ administration represent the severity or stage of regional hemodynamic failure as assessed by positron emission tomography (PET). We studied to elucidate whether ACZ challenge $^{123}I-IMP$ brain single photon emission tomography (SPECT) can accurately grade the seventy of regional hemodynamic failure. Materials and Methods: Eighteen patients (M: 16, F: 2, average age: 61 years) with unilateral occlusive disease of the internal carotid artery or the trunk of the middle cerebral artery (MCA). Patients undewent $^{123}I-IMP$ brain SPECT study with acetazolamide challenge and PET study was carried out within 2 weeks before and after SPECT study. Five healthy volunteers with a mean age of 48 years (range: 28-73 yr, M: 3, F: 2) underwent PET studies to determine normal values. In SPECT study, an asymmetry index (Al)-the percentage of radioactivity of region of interest (ROI) in the occlusive cerebrovascular lesion to the contralateral homologous ROI-was used for numerical evaluation of relative $^{123}I-IMP$ distribution. In PET study, regional CBF, oxygen extraction fraction (OEF), cerebral metabolic rate of oxygen ($CMRO_2$) and cerebral blood volume (CBV) values were measured with $^{15}O-labeled$ gas inhalation method and the values were used for comparison with Al (Al during acetazolamide challenge-Al of basal study) on the SPECT study. ROls were classified by severity into three groups (normal, stage I and stage II). Results: Mean values of Al in areas with normal, stage I and stage II hemodynamic failure were $6.25{\pm}7.77%\;(n=107),\;-10.38{\pm}10.41%\:(n=117)\;and\;13.30{\pm}10.51%\;(n=140)$, respectively. Al significantly differed with each groups (p<0.05). Correlation between Al and CBF, OEF and CBV/CBF in hemisphere with occlusive cerebrovascular lesion was 0.20 (p<0.01), -0.28 (p<0.01) and -0.28 (p<0.01), respectively. Conclusion: We concluded that $^{123}I-IMP$ brain SPECT with acetazolamide challenge could determine the severity ad stage of regional hemodynamic failure as assessed by PET.

• Proceedings of the Korea Society of Poultry Science Conference
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• 2002.11a
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• pp.103-105
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• 2002

This study was conducted to determine how broiler performance with the level of crude protein(23 CP%, 21 CP% and 19 CP%) can be changed and affected, adding Alum(Al$_{2}$(SO$_{4}$)$_{3}$ㆍ14H$_{2}$O) and no Alum in litter(two ALUM levels and 3 Protein levels with 2$\times$3 factorial design). Alum was added as a top dressing to the litter at a rate of 200g ALUM / kg of rice bran. With the exception of the protein levels for feed ：gain(P〈 0.05), there were no significant differences in feed intake, weight gain and feed ：gain of chicks. For ammonia gas emission, both the main effects of Alum and protein(P〈 0.01 and 0.05) at 3weeks and interaction between Alum and protein(P〈 0.05), the main effect of Alum(P〈 0.01) at 6weeks did affected them. In litter excluded the main effects of Alum(P〈 0.05), there was a significant difference among N contents ranged from pH to the rate of C： Organic-N(P〈 0.01).