• Journal of Welding and Joining
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• v.26 no.6
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• pp.54-58
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• 2008

Laser welding with AZ61 filler wire was carried out to improve formability though reduction of porosity and formation of under fill bead. Optimum welding condition and mechanical properties of butt joint for $400{\times}500{\times}1.3mm$ magnesium sheets were studied. Optimal welding conditions of laser power, welding speed, and defocusing length are 1000W, 3m/min, and 2mm, respectively. Results of tensile test indicated that both tensile strength and elongation of specimens welded with filler wire were improved at room temperature because of reduction of porosity and under-filled bead formation in addition to the precipitation hardening and microstructure refinement by Al-Mn and Mg-Al-Zn precipitates. At elevated temperature of $200{\sim}350^{\circ}C$, fracture location of tensile specimen was shifted from weld metal to base metal, indicating less softening of weld metal than base metal.

• Korean Journal of Materials Research
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• v.14 no.12
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• pp.851-856
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• 2004

The aim of this study is to investigate the optimum drawing parameter for BAS121 welded tubes. The BAS121 aluminium alloy tubes with 25 mm in external diameter and 1.3 mm in thickness for heat-exchangers were manufactured by high frequency induction welding with the V shaped convergence angle $6.5^{\circ}$ and power input 55 kW. With increasing the reduction of area ($13,\;21\%$) by drawing, tensile strength was increased and elongation was decreased. With increasing the reduction of area by drawing, hardness in weld metal increased rapidly, while that of base metal increased slowly. In the specimen with the outer diameter smaller than 22 mm, hardness of weld metal was higher than that of base metal. The optimum drawing parameter of area reduction in BAS121 alloys was estimated about $13\%$ because of the work hardening of welds.

• The korean journal of orthodontics
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• v.15 no.2
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• pp.261-269
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• 1985

The purpose of this study was to measure and compare tensile strength for 3 types of new direct-bond brackets and the same brackets after recycling and to evaluate recycled brackets to determine the extent of physical alteration after recycling. Three types of new direct-bond brackets were bonded to recently extracted human premolar teeth and the tensile strength was measured by Universal Testing Machine. The brackets were recycled by thermal process and the tensile test was repeated. To determine the extent of physical alteration after recycling, the slot width and the hardness of metal brackets were measured and to analyze the microstructure of the brackets, photographs of the bracket microstructure were taken. Following results were obtained: 1. The tensile strength of recycled brackets was lower than that of new brackets, but there was no statistically significant difference. (p>0.05) 2. In the new and recycled brackets, the tensile strength of mini-mesh base bracket was statistically higher than that of conturlok base bracket, $(p\leq0.05)$ but there was no statistically significant difference between production of other companies. (p>0.05) 3. The slot width of metal bracket was enlarged from 0.459mm to 0.469mm as a result of the recycling process. (p>0.005) 4. As temperature was increased in thermal treatment, the grains of bracket metal gradually became coarser and the hardness was decreased.

• Nuclear Engineering and Technology
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• v.44 no.5
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• pp.491-500
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• 2012

The dissimilar metal joints welded between Ni-based alloy, Alloy 690 and low alloy steel, A533 Gr. B with Alloy 152 filler metal were characterized by using optical microscope, scanning electron microscope, transmission electron microscope, secondary ion mass spectrometry and 3-dimensional atom probe tomography. It was found that in the weld root region, the weld was divided into several regions including unmixed zone in Ni-base alloy, fusion boundary, and heat-affected zone in the low alloy steel. The result of nanostructural and nanochemical analyses in this study showed the non-homogeneous distribution of elements with higher Fe but lower Mn, Ni and Cr in A533 Gr. B compared with Alloy 152, and the precipitation of carbides near the fusion boundary.

• Journal of Surface Science and Engineering
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• v.50 no.6
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• pp.498-503
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• 2017

The aim of the present study is to evaluate electrochemical corrosion characteristics of base metal and weldment of Al-Mg alloy in seawater solution. The specimen was 5mm thick 5083-H321 Al alloy plate which was butt-welded using gas metal arc welding (GMAW). To identify the types of inclusions in the weldment, the microstructural observation was performed along with Energy dispersive spectrometer (EDS) analysis. The anodic polarization experiments were performed to evaluate the corrosion characteristics. After the anodic polarization test, the corroded surface was observed by SEM(scanning electron microscope) and EDS. The result of the analysis revealed a large number of voids in the weldment, especially coarse grains and inclusions in the heat affected zone. The corrosion current density of the weldment was found to be approximately 13 times higher than that of the base metal, indicating lower corrosion resistance of the weldment due to the defects in the weldment and the heat affected zone.

• Nuclear Engineering and Technology
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• v.53 no.2
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• pp.572-582
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• 2021

This study investigated the creep and creep crack growth (CCG) behavior of the base metal (BM), weld metal (WM), and heat affected zone (HAZ) in a Gr. 91 weldment, which was made by a shield metal arc weld process. A series of tensile, creep, and CCG tests were performed for the BM, WM, and HAZ at 550 ℃. Creep behavior of the BM, WM, and HAZ was analyzed in terms of various creep laws; Norton's power-law, Monkman-Grant relation and damage tolerance factor (λ), and their constants were determined. In addition, each CCGR law for the BM, WM, and HAZ was proposed and compared in terms of a C^*-fracture parameter. The WM and HAZ revealed faster creep rate, lower rupture ductility, and faster CCGRs than the BM, but they showed a similar behavior in the creep and CCG. The CCGRs obtained in the present study exhibited a marginal difference when compared with those of RCC-MRx of currently elevated design code in France. A creep crack path in the HAZ plane progressed towards a weak fine-grained HAZ adjacent to the BM.

• Journal of Advanced Marine Engineering and Technology
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• v.9 no.2
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• pp.126-142
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• 1985

The plane bending corrosiion fatigue test for the welded metal parats was performed in the air and in the natural sea water with and without applying cathodic protection. The specimens tested were the weld of SM41 steel plates, SM58 steel plates and of SM41 to SM58, which were all prepared by submerged arc welding. The main results obtained from the experiment are summarized as follows: (1) In case with SM41 and SM58 steel plates, lower value of impact strength, higher value of hardness and more noble electrode potential were observed in the welded metal part than in the HAZ and base metal. Also the lowest hardness zone in the HAZ was observed with SM58 which was not found with SM41. In case with weld specimen of SM41 to SM58, the impact strength and the electrode potential of the welded metal part showed again the lowest and most noble value but the hardness value was located between those of SM41 and SM58 base metal. (2) In the fatigue test, the specimens tested in the air and under the cathodic protection were both cracked in a purely mechanical mode, but the specimens tested without cathodic protection were cracked by the combination of mechanical fracture and electro-chemical corrosion. (3) The corrosion fatigue limit of the welded metal parts of the specimen was increased by the cathodic protection. As the protection potential was varied down to -800 mV vs. SCE the fatigue limit was increased to the value tested in the air, and the maximum fatigue limit appeared at the -1, 000 - -1, 200 mV vs. SCE. However, as the protection potential was further decreased below -1, 200 mV vs.SCE, the fatigue limit of weld of SM58 and of SM41-SM58 joining was decreased but the limit was almost constant in the case of weld of SM41. (4) It is suggested that when designing steel ship the corrosion fatigue limit of welded metal parts should be stressed as a designing strength of the structure of steel ship in addition to the conventional basis considering simply tensile strength of steel and safety factor.

• Journal of Welding and Joining
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• v.34 no.2
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• pp.46-53
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• 2016

Effect of heating rate on microstructure of brazed joints with STS 304 Printed Circuit Heat Exchanger (PCHE),which was manufactured as large-scale($1170(L){\times}520(W)){\times}100(T)$, mm), have been studied to compare bonding phenomenon. The specimens using MBF 20 was bonded at $1080^{\circ}C$ for 1hr with $0.38^{\circ}C/min$ and $20^{\circ}C/min$ heating rate, respectively. In case of a heating rate of $20^{\circ}C/min$, overflow of filler metal was observed at the edge of a brazed joints showing the height of filler metal was decreased from $100{\mu}m$ to $68{\mu}m$. At the center of the joints, CrB and high Ni contents of ${\gamma}$-Ni was existed. For the joints brazed at a heating rate of $0.38^{\circ}C/min$, the height of filler was decreased from $100{\mu}m$ to $86{\mu}m$ showing the overflow of filler was not appeared. At the center of the joints, only ${\gamma}$-Ni was detected gradating the Ni contents from center. This phenomenon was driven from a diffusion amount of Boron in filler metal. With a fast heating rate $20^{\circ}C/min$, diffusion amount of B was so small that liquid state of filler metal and base metal were reacted. But, for a slow heating rate $0.38^{\circ}C/min$, solid state of filler metal due to low diffusion amount of B reacted with base metal as a solid diffusion bonding.

• Economic and Environmental Geology
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• v.23 no.2
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• pp.183-199
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• 1990

Ore deposits of Dongwon mine are composed of numerous gold and silver veins emplaced in sedimentary rocks of Cambrian Choseon Supergroup and granitoids of Cretaceous age. Ore veins of the mine can be divided into gold and silver veins on the base of vein structure, mineral assemblage and vein trends. Mutual relationships between gold and silver veins are uncertain. Gold veins are simple veins which are composed of base-metal sulfides, and electrum with quartz and ankerite. On the other hand, silver veins are complex veins which reveal three distinct stages of mineral deposition based on vein structure; stage I, deposition of small amounts of oxides and pyrite with quartz; stage II, deposition of base-metal sulfides, small amounts of Ag-bearing minerals, calcite and quartz; stage III, deposition of base metal sulfides, electrum, Ag-sulfosalts, native silver, carbonates and quartz. Homogenization temperature and salinity of fluid inclusion from quartz of gold vein are as follows; $229^{\circ}$ to $283^{\circ}C$, 4.7 to 6.4 wt.% equivalent NaCI. The ore mineralogy suggests that temperature(T) and sulfur fugacity($fs_2$) of the formation of the gold vein and stage III of silver vein are estimated as T ; $294^{\circ}$ to $318^{\circ}C$, $fs_2\;10^{-9.4}$ to $10^{-10.1}$ atm. and T; $240^{\circ}$ to $279^{\circ}C$, $fs_2;10^{-11.1}$ to $10^{-17.3}$ atm. respectively. Pressure condition during gold vein formation estimated from data of ore mineralogy and fluid inclusion range 500 to 750 bar.

• Journal of Korea Foundry Society
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• v.16 no.6
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• pp.523-536
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• 1996

This paper relates to fabrication processing analysis of metal matrix composites by the injection of liquid metal into a fibrous preforms. One dimensional heat transfer analysis during squeeze infiltration process of aluminum base composites has been studied. An analysis method was investigated for the temperature distribution, infiltration velocity and melt infiltration characteristics with the commercial preform with short fiber array. When molten metal is infiltrated in a fibrous preform with random orientation, phase transformation will be occurred in a region such as molten metal, solidified region, preform region and infiltration composites region. a mathematical modelling for a solidification phenomena in fabrication process of metal matrix composites using a squeeze infiltration technique was investigated by the basic relations for liquid metal into a fibrous preform. The temperature distribution of theoretical results was compared with experimental data.