• Journal of Surface Science and Engineering
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• v.36 no.2
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• pp.176-184
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• 2003

New lubricant film of organic and inorganic composite resin was developed to improve the press formability of galvannealed steel sheets (GA) for automotive body panels. The frictional coefficient of lubricant GA steel sheets is about 20% superior to that of uncoated GA. The current range of spot welding of lubricant GA is similar to that of the uncoated GA, but the burning trace of spot welding is inferior to that of the uncoated GA in the oiling condition. The alkaline degreasability of lubricant GA shows 100% in alkaline degreasing condition of automotive company. The size and shape of the phosphated coating layer are similar to those of the uncoated GA sheet. The powdering property of the lubricant GA gives rise to 20∼50% improved property compared with the uncoated GA sheet.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.04a
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• pp.154-161
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• 2001

A procedure of the design optimization for steel box girder bridges using micro genetic algorithms(μGA) is developed. The effect of population size is investigated and the efficiency and reliability of μGA is demonstrated in the optimum design of steel box girder bridges. Optimum design problems of steel box girder bridges are formulated, where tile design of concrete slab is based on the USD specifications and steel box girder based on LRFD respectively. Design of optimizations of single-span and 2-span steel box girder bridges are performed with the population size of 5, 40, 80, and 120, respectively The μGA-based optimum design of the 3-span steel box girder bridge is compared with SQP results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.4
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• pp.747-754
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• 1988

High strength steels (HS) of dual phase and monogalvanized steel sheets (GA ; plated plane, GAB ; bare plane0 were used to investigate the fatigue strengths of four kinds of single-spot-welded joint specimen under tensile-shear repeated load. The specimen is classified as the same mating metal specimen (HS*HS, GA*GAB) and different mating metal specimen (HS*GA, HS*GAB). Some of the results are ; (1) Static tensile load of single-spot-welded joint specimens is proportional to tensile strength of metal and rigidity of mating metal sheet. (2) Fatigue life of HS*HS specimens increased about 20% longer than that of GA*GAB specimens in low cycle range. (3) In different mating metal specimens, the fatigue life of HS*GA specimens increased about 84% more that of HS*HS specimens in high cycle range.

• Journal of Welding and Joining
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• v.19 no.1
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• pp.58-64
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• 2001

The initiation and propagation lives of fatigue crack were studied for spot weldments composed of cold rolled steel plates(SPC$\times$SPC) and galvanized steel plates(GA$\times$GA) using DC potential drop method(DCPDM). Through the various test results, it was known that the fatigue crack initiation and propagation behaviors in all specimens could be definitely detected by DCPDM. The fatigue crack initiation life( $N_{i}$) detected by DCPDM in SPC$\times$SPC and GA$\times$GA spot weldments increased as the welding current and the nugget diameter( $N_{d}$) increased. The fatigue crack propagation life($\Delta$ $N_{f-i}$) declined as the difference of $N_{i}$ and the fatigue fracture life( $N_{f}$) also increased according to the decrease of fatigue load, $\Delta$P and the increase of nugget diameter. In the same spot weldments, the increase of nugget diameter came to increase fatigue crack propagation life owing to a decrease of stress concentration in front of nugget, especially the increasing extent for GA$\times$GA spot weldment was very high. In the welding current 6kA, $N_{f}$ for GA$\times$GA spot weldment decreased more than that of SPC$\times$SPC specimen due to zinc layer coated in steel plate and undersized nugget diameter. On the other hand, in 8kA and 10kA, the GA$\times$GA spot weldment showed higher $N_{f}$ in spite of lower $N_{i}$, than that of SPC$\times$SPC specimen except 3,000N fatigue load.ue load. load.d.

• Corrosion Science and Technology
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• v.9 no.2
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• pp.74-80
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• 2010

For the purpose of applying a hot-dip Zn-6mass%Al-3mass%Mg alloy coated steel sheet (ZAM) to automotive body materials, a laboratory study of the general properties required for inner and outer panels of automotive bodies was performed. Even with only light coating weight, ZAM showed an excellent corrosion resistance in terms of both cosmetic and perforation corrosion compared to the currently used materials for automotive bodies, GI70 and GA45. In our study, it was confirmed that ZAM exhibits as good as or better properties than GI70 in terms of spot weldability and press formability. Furthermore, since the same corrosion resistance can be achieved with less coating weight by applying ZAM, laser weldability is better than GI and GA.

• Corrosion Science and Technology
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• v.20 no.1
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• pp.7-14
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• 2021

PosMAC^® is a brand of Zn-Mg-Al hot-dip coated steel sheet developed by POSCO. PosMAC^® can form dense surface oxides in corrosive environments, providing advanced corrosion resistance compared to traditional Zn coatings such as GI and GA. PosMAC^® 3.0 is available for construction and solar energy systems in severe outdoor environments. PosMAC^®1.5 has better surface quality. It is suitable for automotive and home appliances. Compared to GI and GA, PosMAC^® shows significantly less weight reduction due to corrosion, even with a lower coating thickness. Thin coating of PosMAC^® provides advanced quality and productivity in arc welding applications due to its less generation of Zn fume and spatters. In repeated friction tests, PosMAC^® showed lower surface friction coefficient than conventional coatings such as GA, GI, and lubricant film coated GA. Industrial demand for PosMAC^® steel is expected to increase in the near future due to benefits of anti-corrosion and robust application performance of PosMAC^® steel.

• Journal of Welding and Joining
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• v.34 no.6
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• pp.28-34
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• 2016

Galvannealed(GA) steels are now generally used in car body manufacturing for corrosion resistance. In this study, the weldability and joint mechanical behavior of a newly developed 1.2GPa grade GA ultra high strength TRIP(transformation induced plasticity) steel was investigated for three joining processes, such as adhesive bonding, resistance spot welding and weldbonding. Under both shear and peel stress conditions, the failure mode of the adhesive joints were the mixture of the adhesive cohesive failure, adhesive interface failure and coating layer failure. It means that the adhesion strength of GA coating onto the base metal was similar to that of adhesive bonding onto the GA coating. Under the shear stress condition, the weldbonding exerted to expand the optimal spot welding condition of 1.2GPa GA TRIP steel because the strength of adhesive bond overwhelmed that of the resistance spot weld. Under the peel stress condition, the weldbonding also exerted to expand the optimal spot welding condition of 1.2GPa GA TRIP steel by inducing the tear fracture mode rather than the partial plug fracture mode.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.389-392
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• 2005

In the modern days, a galvannealed sheet steel(GA) instead of a cold rolled steel sheet has been widely used as an alternative to extend the life of automotive body. Accordingly, the mechanical properties of GA for automobiles were taken Into account and studied by comparing with the temperature variation on annealing in this study. To clarify the effect of surface features in the mechanical properties of GA, the several tests such as nanoindentation and FE-analysis were executed. For this goal use is made of the method of neural networks. The developed neural networks apply also to obtain reliable mechanical properties of the thin films. Load-displacement curve was computed by the analysis procedure and compared with experimental results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1575-1578
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• 2005

As GA(Galvannealed sheet steel, GA) has good corrosion resistance, weldability and paintability as well as excellent stamping formability it's demand is rapidly increasing for automotive panel. But the layer of the Galvannealed sheet steel is easy to have a coating layer such as powdering and flaking in the press process because it is composed of Fe-Zn alloy. Therefore, the process condition is properly required to form the surface treated sheet steel. The frictional characteristics with dies are changed according to the annealing temperature, $505^{\circ}C,\;515^{\circ}C\;and\;540^{\circ}C$ during the process. To obtain the frictional characteristics of GA sheet steel in this study, on flat friction test is conducted. The friction coefficient is compared with the variation of pressure and velocity, viscosity of lubricant at the various galvannealed temperatures.

• Korean Journal of Metals and Materials
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• v.46 no.8
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• pp.495-505
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• 2008

With the high proportion of zinc coated steels in body-in-white assembly, newly developed surface roughness textured galvannealed steel sheets have been introduced. In this study, zinc coated and surface roughness textured steel sheets were welded by resistance spot welding to investigate its weldability including electrode wear test. Based on the results of tensile-shear test, nugget diameter changes, and electrode tip growth test, it was clear that both surface roughness textured steels (GA-T and GA-E) showed good weldability. Also, there was no large difference in weldability and electrode wear behavior between GA-T and GA-E steels which have different surface roughness morphology. An analysis of electrode degradation showed Fe and Zn penetration through the electrode tip surface at 2400 welds reached $55{\sim}60{\mu}m$ and $75{\sim}80{\mu}m$, respectively. Therefore, there is no significant effect of surface roughness morphology on spot weldability of surface roughness textured galvannealed steel sheets. However, slight difference in thickness of alloying layers existing on electrode tip was found between GA-T and GA-E steels.