• Journal of the Korean institute of surface engineering
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• v.54 no.2
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• pp.62-70
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• 2021

Al2024 aluminum alloy specimens were exposed to atmospheric conditions for maximum 24 months and analyzed by electron microscopes to characterize their corrosion behavior and oxide film characteristics. As the exposure time increased from 12 months to 24 months, the number of pitting sites per 1 mm² increased from ~100 to ~200. The uniform oxidation (or non-pitting) region of the 12-month exposure specimen showed 30~120 nm thick oxide layer, whereas the 24-month exposure specimen showed 170~200 nm thick oxide with the local oxygen penetration region up to 1 ㎛ deep. There was no local corrosion area observed in the 12-month exposure specimen except pitting. However, in the 24-month exposure specimen, local oxygen penetration region was observed beneath the uniform oxide layer and near the pitting cavity. Al2024 showed two times thicker uniform oxide layer but much shallower local oxygen penetration region than Al1050, which appears to be related to low Si concentration. Further research is needed on the effects of Mg segregation near the tip of the oxygen penetration region.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.384-386
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• 2005

Initial oxide layer on the butt surface fragments during friction stir welding (FSW) and then often remains as a faint zigzag-line pattern on the cross section. When remnant of the oxide layer often adversely affects the mechanical properties in the weld, it is called as 'kissing-bond'. The present study systematically examines effect of oxide array on bend property in the root of friction stir (FS) welded Al alloy 1050 by transmission electron microscopy (TEM), and then clarifies identity of the kissing-bond.

• Journal of the Korean institute of surface engineering
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• v.50 no.5
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• pp.421-426
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• 2017

Herein, we investigated surface morphological characteristics of anodic films on Al6061 alloy prepared by unipolar pulsed Micro-arc oxidation (MAO) in a mixed solution of $Na_2SiO_3$ + KOH. The number and size of pores as well as craters on anodic alumina surface were studied as a function of different voltages, duty cycles and applied anodic current densities. The morphological characteristics of all samples were investigated by scanning electron microscopy, conforming that the most uniform surface morphology of MAO films on Al1050 alloy was obtained at high applied current density with low duty cycle.

• Journal of the Korean institute of surface engineering
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• v.48 no.2
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• pp.68-72
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• 2015

The corrosion behavior of metals and alloys for the safety of offshore structures in seawater was investigated for the application of sacrificial anodes. The experiments were focused on the polarization behaviors and the surface morphology of each metal after experiments. Pure Zn, pure Al (Al1050), Al alloys (Al5052, Al6061), Mg alloys (AZ31, AZ91D) and steel (SCM440) were assessed in 3.5% sodium chloride solution by means of potentiodynamic polarization to verify the galvanic corrosion potential ($E_{couple}$). Potentiostat plots were plotted to compare the surface and corrosion current density ($i_{couple}$) of metals as sacrificial anodes in seawater to protect steel alloy as a cathode. Al alloys showed the best performance as a sacrificial anode, on the other hand, Mg alloys showed overprotection behavior. The surface morphologies of sacrificial anodes were observed by FESEM and compared.

• Journal of the Korean Society of Industry Convergence
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• v.20 no.3
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• pp.221-232
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• 2017

In this study, bipolar plates in fuel cells are formed using rubber forming process. The effects of important parameters in rubber forming such as hardness and thickness of rubber pad, speed and pressure of punch that compress blank, and physical property of materials on the channel depth were analyzed. In the soft material sheet Al1050, deeper channels are formed than in materials STS304 and Ti-G5. Formed channel depth was increased when hardness of rubber pad was lower, thickness of rubber pad was high, and speed and pressure of punch were high. It was found the deepest channel was achieved when forming process condition was set with punch speed and pressure at 30 mm/s and 55 MPa, respectively using rubber pad having hardness Shore A 20 and thickness 60 mm. The channel depths of bipolar plates formed with Al1050, STS304 and Ti-G5 under the above process condition were 0.453, 0.307, and 0.270 mm, respectively. There were no defects such as wrinkle, distortion, and crack found from formed bipolar plates.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.148-151
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• 2005

A study on the microstructure and the texture of the samples after ECAP and subsequent heat treatment has been carried out. The specimens after ECAP showed a very fine grain size, a decrease of <100> // ND, and an increase of <111> // ND textures. The $\{111\}<112>,\;\{123\}<634>,\;\{110\}<001>,\;\{112\}<111>,\;\{110\}<111>,\;and\;\{013\}<231>$ texture components were increased in the specimens after the ECAP and subsequent heat-treatment at $400^{\circ}C$ for 1 hour. One of the most important properties in sheet metals is formability. The r-value or plastic strain ratio has been used as a parameter that expresses the formability of sheet metals. The change of the plastic strain ratios after the ECAP and subsequent heat-treatment conditions has been investigated and it was found that they were two times higher than those of the initial Al sheets. This could be attributed to the formation above texture components through the ECAP and subsequent heat-treatment.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.4
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• pp.791-796
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• 2001

Friction stir welding is a solid phase welding process that does not melt the metal when welding. The FSW is the most remarkable and potentially useful new welding technique that is still in development. Friction stir butt welding process on 2 mm thick Al 1050 plates by utilizing a milling machine was experimentally studied. With the optimized heat generating tool welds could be achieved that are void and crack free. It was found that the friction stir welded tensile test specimens failed in the HAZ outside of the weld metal, and that the tensile strength was above 90% of that of the base metal.

• Transactions of Materials Processing
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• v.28 no.3
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• pp.135-144
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• 2019

Electromagnetic impulse welding (EMIW) is a type of solid state welding using the Lorentz force generated by interaction between the magnetic field of the coil and the current induced in the workpiece. Although many experimental studies have been investigated on the expansion and compression welding of tube using the EMIW process, studies on the EMIW process of lap joint between flat sheets are uncommon. Since the magnetic field enveloped inside the tube can be controlled with ease, the electromagnetic technique has been widely used for tube welding. Conversely, it is difficult to control the magnetic field in the flat sheet welding so as to obtain the required welding velocity. The current study analyzed the effects of coil shape on the impulse velocity for suitable flat one-turn coil for the EMIW of the flat sheets. The finite element (FE) multi-physics simulation involving magnetic and structural field of EMIW were conducted with the commercial software LS-DYNA to evaluate the several shape variables, viz., influence of various widths, thicknesses, gaps and standoff distances of the flat one-turn coil on the impulse velocity. To obtain maximum impulse velocity, the flat one-turn coil was designed based on the FE simulation results. The experiments were performed using an aluminum alloy 1050 sheets of 1.0mm thickness using the designed flat one-turn coil. Through the microscopic interfacial analysis of the welded specimens, the interfacial connectivity was observed to have no defects. In addition, the single lap joint tests were performed to evaluate the welding strength, and a fracture occurred in the base material. As a result, a flat one-turn coil was successfully designed to guarantee welding with bond strength equal to or greater than the base material strength.

• Transactions of Materials Processing
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• v.24 no.4
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• pp.293-298
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• 2015

A safety vent is crucial to protect its user from unpredictable explosions caused by increasing internal pressure of the lithium-ion batteries. In order to prevent the explosion of the battery, a safety vent rupture is required when the internal pressure reaches a critical value. In conventional manufacturing, the cap plate and the safety vent are fabricated separately and subsequently welded to each other. In the current study, a manufacturing process including a backward extrusion and coining process is suggested to produce an integral safety vent which also has the benefit of increasing production efficiency. FE simulations were conducted to predict the rupture pressure and to design the safety vent using a ductile fracture criterion and the element deletion method. The critical value, C, in the ductile fracture criterion was obtained from uniaxial tensile tests with an annealed sheet of 1050-H14 aluminum alloy. Rupture tests were preformed to measure the rupture pressure of the safety vent. The results met the required rupture pressure within 8.5±0.5 kgf/cm². The simulation results were compared with experimental results, which showed that the predicted rupture pressures are in good agreement with experimentally measured ones with a maximum error of only 3.9%.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1045-1050
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• 2003

In this study, to investigate the effects of omitting low-amplitude cycles from a flight-simulation loading, crack growth tests are conducted on 2124-T851 aluminum alloy specimens. Three test spectra are generated by omitting small load ranges as counted by the rain-flow count method. The crack growth test results are compared with the data obtained from the flight-simulation loading. The experimental results show that omission of the load ranges below 5% of the maximum load does not significantly affect crack growth behavior, because these are below the initial stress intensity factor range. However, in the case of omitting the load ranges below 15% of the maximum load, crack growth rates decrease, and therefore crack growth curve deviates from the crack growth data under the flight-simulation loading. To optimize the load range that can be omitted, crack growth curves are simulated by the stochastic crack growth model. The prediction shows that the omission level can be extended to 8% of the maximum load and test time can be reduced by 59%.