• Journal of Welding and Joining
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• v.33 no.6
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• pp.55-59
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• 2015

Self-piercing riveting (SPR) is a sheet-joining method that can be used for materials that are difficult or unsuitable for weld, such as aluminum alloys and other steel sheet metals. The increased application of lightweight materials has initiated many investigations into new SPR conditions for riveting dissimilar materials. However, buckling of the semi-tubular rivet occurs during the riveting of AHSS. In this study, a helical SPR was designed for the riveting of AHSS and Al-alloy. In addition, the reinforced helical SPR which has straight parts was designed. The riveting of AHSS and Al-alloy was simulated. Simulated results were verified by comparison with experimental ones.

• Archives of Metallurgy and Materials
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• v.64 no.3
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• pp.875-878
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• 2019

Microstructures and mechanical properties of as-cast Al-6.5Mg-1.5Zn-0.5Fe alloys newly alloy-designed for the parts of automobile were investigated in detail. The aluminum (Al) sheets of 4 mm thickness, 30 mm width and 100 mm length were reduced to a thickness of 1mm by multi-pass rolling at ambient temperature and subsequently annealed for 1h at 200~500℃. The as-cast Al sheet was deformed without a formation of so large cracks even at huge rolling reduction of 75%. The recrystallization begun to occur at 250℃, it finished at 350℃. The as-rolled material showed tensile strength of 430 MPa and tensile elongation of 4.7%, however the specimen after annealing at 500℃ showed the strength of 305 MPa and the elongation of 32%. The fraction of high angle grain boundaries above 15 degree increased greatly after annealing at high temperatures. These characteristics of the specimens after annealing were discussed in detail.

• Journal of the Korean Society of Mechanical Technology
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• v.20 no.6
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• pp.886-893
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• 2018

In this study, clinching characteristics of aluminum and galvanized steels were investigated for the application of clinching as a joining technique to aluminum wheelhouse assembly. A6451 aluminium alloy and galvanized steel sheets were joined by hybrid joining(clinching + adhesive bonding). Tensile-shear load and fracture mode of hybrid joints were investigated. Maximum tensile-shear load of hybrid joints was about six times higher than that of clinched joints without adhesive. Energy absorption values of hybrid joints were higher than those of clinched joints without adhesive as well as resistance spot welded steel joints. Developed aluminum wheelhouse assembly showed higher static stiffness than the existing steel parts. Aluminum wheelhouse inner panel unit was 44% lighter than the steel unit, and the final assembled aluminum wheelhouse was 14.6% lighter than the existing steel parts.

• Transactions of Materials Processing
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• v.20 no.3
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• pp.257-264
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• 2011

Multilayer(clad) sheets, composed of two or more materials with different properties, are fabricated using the roll-bonding process. A good formability is an essential property for a multilayered sheet in order to manufacture parts by plastic deformation. In this study, the influences of temperature and strain rate on the plastic properties of stainless steel-aluminum-magnesium multilayered(STS-Al-Mg) sheets were investigated. Tensile tests were performed at various temperatures and strain rates on the multilayered sheet and on each separate layer. Fracture of the multilayered sheet was observed to be temperature-dependent. At the base temperature of $200^{\circ}C$, all materials fractured simultaneously. At lower temperatures, the Mg alloy sheet fractured earlier than the other materials. Conversely, the other materials fractured earlier than the Mg alloy sheet at higher temperatures. The uniform and total elongations of the multilayered sheet were observed to be higher than that of each material at a temperature of $250^{\circ}C$. Larger uniform elongations were obtained for higher strain rates at constant temperature. The same trend was observed for the Mg alloy sheet, which exhibited the lowest elongation among the three materials. The tensile strengths and elongations of the single layer sheets were compared to those of the multilayer material. The strength of the multilayered sheet was successfully calculated by the rule of mixture from the values of each single layer. However, no simple correlation between the elongation of each layer and that of the multilayer was obtained.

• Transactions of Materials Processing
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• v.24 no.4
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• pp.256-263
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• 2015

Electric resistance spot welding has been used to join overlapped steel sheets in automotive bodies. Recently to reduce weight in automotive vehicles, non-ferrous metals are being used or considered in car bodies for hoods, trunk lids, doors parts, etc. Various welding processes such as laser welding, self-piercing rivet, friction stir welding are being used. In the current study, a new electric resistance heated friction stir spot welding is suggested for the spot welding of non-ferrous metals. The welding method can be characterized by three uses of heat -- electric resistance heating, friction stir heating and conduction heating of steel electrodes -- for the fusion joining at the interfacial zone between the two sheets. The welding process has variables such as welding current, diameter of the steel electrodes, revolutions per minute (rpm) of the friction stir pin, and the insert depth of the stir pin. In order to obtain the optimal welding variables, which provide the best welding strength, many experiments were conducted. From the experiments, it was found that the welding strength could be reached to the required production value by using an electrode diameter of 10mm, a current of 7.6kA, a stirring speed of 400rpm, and an insert depth of 0.8mm for the electric resistance heated friction stir spot welding of 5052 aluminum 1.5mm sheets.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.231-237
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• 2000

A15052/AFRP laminates were developed principally to obtain a material with good fatigue strength, in which possible cracks would grow very slowly. Weight savings of more than 30% should be attainable in practice. Also, the crack bridging fibers could still was carry a significant part of the load over the crack, thus the COD and stress intensity factor was reduced at the crack tip. A15052/ AFRP laminates consists of three thin sheets of 5052-H34 aluminum alloy and two layers of [0] unidirectional aramid fiber prepreg. The cyclic-bending moment test was investigated based on applying the five kinds of bending moments. The size of the delamination zone produced between 5052-H34 aluminum alloy sheets and fiber-adhesive layers was measured from ultrasonic C-scan pictures taken around the fatigue crack. In addition, the relationship between the cyclic-bending moment and the delamination zone size was studied and the effect of fiber bridging mechanism was also considered.

• Journal of the Korean Society of Safety
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• v.30 no.4
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• pp.1-7
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• 2015

Self-piercing riveting (SPR) process is gaining popularity due to its many advantages. The SPR does not require a pre-drilled hole and has capability to join a wide range of similar or dissimilar materials and combinations of materials. This study investigated the fatigue strength of self-piercing rivet joint with aluminum alloy (Al-5052) and steel (SPCC) sheets. Static and fatigue tests on tensile-shear specimens were conducted. From the static strength aspect, the optimal punching force for the specimen with upper SPCC (U.S) sheet and lower aluminum alloy(L.A) sheets was 34 kN. During static test the specimens fractured in pull-out fracture mode due to influence of plastic deformation of joining area. There was a relationship between applied load amplitude $P_{amp}$ and number of cycles N ; $P_{amp}=19588N_f^{-0.211}$ and $P_{amp}=4885N_f^{-0.083}$ for U.S-L.A and U.A-L.S specimens, respectively. U.A-L.S fatigue specimens failed due to fretting crack initiation around the rivet neck between upper and lower sheets.

• Journal of Institute of Convergence Technology
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• v.5 no.1
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• pp.7-12
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• 2015

Sheet metal formability can be defined as the ability of metal to deform without necking or fracture into desired shape. Every sheet metal can be deformed without failure only up to a certain limit, which is normally known as forming limit curve(FLC). In this paper, the dome stretching tests and tensile tests have been performed to obtain forming limit curve of aluminum alloy. During the experiment, failure strain is measured using digital image correlation(DIC) method. DIC method is a whole-field measurement technique that acquires surface displacements and strains from images information which characterized a random speckle as intensity grey levels. Recently years, this DIC method is being developed and used increasingly in various research. DIC results demonstrated the usefulness and ability to determine a strain.

• Transactions of Materials Processing
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• v.14 no.6 s.78
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• pp.553-558
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• 2005

A study on the microstructure, the texture and the formability of the samples after ECAPed and subsequent heat-treated AA 1050 aluminum alloy sheet have been carried out. The specimens after the 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 was as a parameter that expressed the formability of sheet metals. The change of the plastic strain ratios after the ECAP and subsequent heat-treatment conditions were 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 of AA 1050 Aluminum alloy sheet.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.118-121
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• 2005

The square cup drawing of magnesium alloy AZ31 $(aluminum\;3\%,\;Zinc\;1\%)$ sheets was studied by experimental approach in various temperatures (200, 250, 300, 350, $400^{\circ}C$) when blank holding force (BHF) was controlled in real-time. And so on, the drawability was measured with the different die and punch coating. The square cup drawing test was performed by three different coated punches (CrN, TiCN, Non-coated). BHF was set about 2.0 KN, forming speed was 50 mm/min, blank thickness were 0.5, 1.0mm and the cup size was 40 mm by 60 mm after forming. The experimental data of square cup drawing test show that the tools coating and temperature were effect on the drawbility.