• Transactions of Materials Processing
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• v.14 no.1 s.73
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• pp.71-77
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• 2005

Thermal stability and dry sliding wear behavior of ultra-fine grained 6061 Al alloy fabricated by an accumulative roll-bonding (ARB) process have been investigated. After 4 ARB cycles, an ultra-fine grained microstructure of the 6061 Al alloy composed of grains with average size of 500nm, and separated mostly by high-angle boundaries was obtained. Though hardness and tensile strength of the ARB processed Al alloy increased with ARB cycles up to 4 cycles, the processed alloy exhibited decreased ductility and little strain hardening. Thermal stability of the ARB-processed microstructure was studied by annealing of the severely deformed alloy at $423K{\sim}573K$. The refined microstructure of the alloy remained stable up to 473K, and the peak aging treatment of the alloy at 450K for 8 hrs increased the thermal stability of the alloy. Sliding-wear rates of the alloy increased with the number of ARB cycles in spite of the increased hardness with the cycles. Wear mechanisms of the ultra-fine grained alloy were investigated by examining worn surfaces, wear debris, and cross-sections by a scanning electron microscopy (SEM).

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.147-150
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• 2001

The ARB (Accumulative Rolling Bonding) Process was applied to a 6061 Al alloy to obtain ultra-fine grains. After 4 ARB cycles at $315^{\circ}C$, original equilibrium large grains were transformed to ultra-fine grains of several hundred nano-meter size with nonequilibrium grain boundaries. At lower number of cycles, microsutcture of highly-tangled dislocation cells were observed. Large grains and coarsened precipitates filled the microstructure of specimens experienced ARB cycles more than 5. Sliding wear tests using a pin-on-disk type wear tester were conducted on the ARB processed 6061 Al alloy plate. Wear rates of the 6061 Al alloy increased with the increase of ARB cycle number as well as the applied load. Worn surfaces and debris, cross-sections of the worn specimen were examined with scanning electron microscopy (SEM) to investigate the wear mechanism of the ultra-fine grained 6061 Al Tensile properties of the 6061 Al alloy were also studied and used to correlate the wear test results with the microstructures, which evolved continuously with the number of ARB cycles.

• Journal of the Korean Society of Safety
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• v.27 no.5
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• pp.42-48
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• 2012

Peel-tension fatigue experiments were conducted for investigating on fatigue strength of mechanical press joints of SPCC steel sheet used in the field of the automobile industry. In addition, finite element method analysis on the peel-tension specimen was conducted using HyperMesh and ABAQUS softwares. The cold rolled mild steel was used to join the T-shaped peel-tension specimen with a button diameter of 5.4 mm and a punch diameter of 8.3 mm. The fatigue limit load amplitude was found to be 112.4 N at the number of cycles 106, indicating that the ratio of fatigue limit load to static peel-tension strength was about 8%. This value suggests that the mechanical press joint is highly vulnerable to peel-tension load rather than to tensile-shear load, considering that the ratio of fatigue limit load to static tensile-shear strength was about 43%. Fatigue failure mode was found to be interface-failure mode.

• Journal of Welding and Joining
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• v.27 no.3
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• pp.52-59
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• 2009

Flash butt welding is applied in many industries. New technology was developed recently for joining billets which called "EBROS (Endless Bar Rolling System)". After reheating billets in furnace, two billets were joined using flash butt welding. The objective of this study was to investigate the effect of alloying elements on mechanical properties of flash butt welded zone of hot rolled steel bar. The tensile properties on welded zone of Fe-Mn steel and Fe-Mn-V steel were dropped as compared with non-welded zone. Fe-Mn-Nb steel was opposed to the former. It was found that the white band at the welded zone had high ferrite volume fraction and large ferrite grain size. The vertical white band between flash butt welded billets was transformed into an arrowhead it of steel bar. According to this band, softening has been appeared. There was a interesting phenomenon with HAZ of Fe-Mn-Nb Steel, 40nm scale of particles were observed and hardness of HAZ was higher than non-welded zone.

• Journal of Welding and Joining
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• v.31 no.1
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• pp.51-57
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• 2013

Residual stress caused in the weldments with high restraint force are often observed during welding in the weldments of Inner and outdoor materials or radial tanks. The reason is that quantitative analysis about thermal stresses during laser welding is lacking for this weldments. To verify Finite Elements Method (FEM) theory, the temperature was measured with thermocouple in a real time in this paper. Also analysis of the thermal stress for welding condition is performed by Comsol program package on various welding condition in SCP1-S butt welding. The principal stress in laser welding process is seen through the width direction. Also, it was confirmed that a change in base metal by thermal expansion made the stress in width direction stronger. Base metal close to the weld bead as the process progresses to the tensile stress in the compressive stress was varied. It was shown that the change of stress was quantitative from the bead at a certain distance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.8
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• pp.649-656
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• 2019

Flux cored arc welding (FCAW), which is used widely in many fields, such as shipyards, bridge structures, construction machinery, and plant industry, is an alternative to shielded metal arc welding (SMAW). FCAW is used largely in the welding of carbon and alloy steel because it can be welded in all poses and obtain excellent quality in the field under a range of working conditions. In this study, the mechanical properties of welded parts were analyzed after different welding of SS400 and SM490A using FCAW. The following conclusions were drawn. The tensile test results satisfied the KS standard tensile strength in the range of 400~510 N/mm2 in all welding positions. The bending test confirmed that most of the specimens did not show surface breakage or other defects during bending and exhibited sufficient toughness, even after plastic deformation. The hardness test results were lower than the standard value of 350 Hv of KS B 0893. Similar to the hardness test, were greater than the KS reference value. The macro test revealed no internal flaws, non-metallic inclusions, bubbles or impurities on the entire cross section of the weld, and there were no concerns regarding lamination.

• Korean Journal of Materials Research
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• v.24 no.11
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• pp.585-590
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• 2014

Microstructural evolution in the thickness direction of an oxygen free copper processed by accumulative rollbonding (ARB) is investigated by electron back scatter diffraction (EBSD) measurement. For the ARB, two copper alloy sheets 1 mm thick, 30 mm wide and 300 mm long are first degreased and wire-brushed for sound bonding. The sheets are then stacked and roll-bonded by about 50% reduction rolling without lubrication at an ambient temperature. The bonded sheet is then cut to the two pieces of the same dimensions and the same procedure was repeated on the sheets up to eight cycles. The specimen after 1 cycle showed inhomogeneous microstructure in the thickness direction so that the grains near the surface were finer than those near the center. This inhomogeneity decreased with an increasing number of ARB cycles, and the grain sizes of the specimens after 3 cycles were almost identical. In addition, the aspect ratio of the grains decreased with an increasing number of ARB cycles due to the subdivision of the grains by shear deformation. The fraction of grains with high angle grain boundaries also increased with continuing process of the ARB so that it was higher than that of the low angle grain boundaries in specimens after 3 cycles. A discontinuous dynamic recrystallization occurred partially in specimens after 5 cycles.

• Journal of Welding and Joining
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• v.31 no.5
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• pp.47-53
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• 2013

We have investigated the traits of clad metals in hot-rolled clad steel plates, including the sensitization and mechanical properties of STS 316 steel plate and carbon steel (A516), under various specific circumstances regarding post heat treatment, multilayered welds, and thick or repeated welds for repair. For evaluations, sectioned weldments and external surfaces were investigated to reveal the degree of sensitization by micro vickers hardness, tensile, and etching tests the results were compared with those of EPR tests. The clad steel plates were butt-welded using FCAW and SAW with the time of heat treatment as the variable, a that was conducted at $625^{\circ}C$, for 80, 160, 320, 640, and 1280 min. Then, the change in corrosion resistance was evaluated in these specimens. With carbon steel (A516), as the heat treatment time increased, the annealing effect caused the tensile strength to decrease. The micro-hardness gradually increased and decreased after 640 min. The elongation and contraction of the area also increased gradually. The oxalic acid etch test and EPR test on STS316 and the clad metal showed STEP structure and no sensitization. From the test results on multi-layered and repair welds, it could be concluded that there is no effect on the corrosion resistance of clad metals. The purpose of this study was to suggest some considerations for developing on-site techniques to evaluate the sensitization of stainless steels.

• Korean Journal of Materials Research
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• v.26 no.7
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• pp.388-392
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• 2016

A cold roll-bonding process was applied to fabricate an AA1050/AA6061/AA1050 laminate complex sheet. Two AA1050 and one AA6061 sheets of 2 mm thickness, 40 mm width and 300 mm length were stacked up after surface treatment that included degreasing and wire brushing; material was then reduced to a thickness of 3 mm by one-pass cold rolling. The laminate sheet bonded by the rolling was further reduced to 1.2 mm in thickness by conventional rolling. The rolling was performed at ambient temperature without lubricant using a 2-high mill with a roll diameter of 210 mm. The rolling speed was 5.0 m/sec. The AA1050/AA6061/AA1050 laminate complex sheet fabricated by roll bonding was then hardened by natural aging T4) and artificial aging (T6) treatments. The microstructures of the as-roll bonded and the age hardened Al complex sheets were revealed by optical microscope observation; the mechanical properties were investigated by tensile testing and hardness testing. The strength of the as-roll bonded complex sheet was found to increase by 2.9 times compared to that value of the starting material. In addition, the hardness of the complex sheets increased with cold rolling for AA1050 and age-hardening treatment for AA6061, respectively. After heat treatment, both AA1050 and AA6061 showed typical recrystallization structures in which the grains were equiaxed; however, the grain size was smaller in AA6061 than in AA1050.

• Korean Journal of Materials Research
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• v.26 no.3
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• pp.154-159
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• 2016

A roll-bonding process was applied to fabricate an AA1050/AZ91/AA1050 laminate complex sheet. Two AA1050 and one AZ91 magnesium sheets of 2 mm thickness, 30 mm width and 200 mm length were stacked up after surface treatment that included degreasing and wire brushing; material was then reduced to a thickness of 3 mm by one-pass cold rolling. The laminate sheet bonded by the rolling was further reduced to 2 mm in thickness by conventional rolling. The rolling was performed at 623K without lubricant using a 2-high mill with a roll diameter of 210 mm. The rolling speed was 15.9 m/min. The AA1050/AZ91/AA1050 laminate complex sheet fabricated by roll bonding was then annealed at 373~573K for 0.5h. The microstructure of the complex sheets was revealed by electron back scatter diffraction (EBSD) measurement; the mechanical properties were investigated by tensile testing and hardness testing. The strength of the complex sheet was found to increase by 11 % and the tensile elongation decreased by 7%, compared to those values of the starting material. In addition, the hardness of the AZ91 Mg region was slightly higher than those of the AA1050 regions. Both AA1050 and AZ91 showed a typical deformation structure in which the grains were elongated in the rolling direction; however, the mis-orientation distribution of grain boundaries varied greatly between the two materials.