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A new 5xxx-series aluminum alloy, which was designed to have an excellent paint-bake-hardenability with practically no room-temperature aging, has been developed for automobile body sheets. The alloy contains 2∼3%Mg with additional amounts of Cu and Si. Yield strength in the as-shipped condition is very low, 80∼100MPa, but it can be increased by as much as about 60MPa through 2% stretch and paint-bake at 170°C. Such an excellent response to paint-bake was revealed to result from Guinier-Preston-Bagaryatskii(GPB) zone formation and enhanced by the optimum addition of Si. Density of vacancies in the alloy was reduced through a special annealing process to suppress room-temperature aging. Press-forming for fender outer and engine hood inner panels was done, and the alloy was demonstrated to have formability superior to 6xxx-series alloys and Al-4.5%Mg alloys, due to the reduced initial yield strength which also suppressed susceptibility to spring back.

Increase of load capacity for trucks by weight reduction of the body has been required to cut down transportation costs. The weight reduction of truck body is feasible in terms of the application of high-strength steel sheet to body. Especially, the application to truck frame is important because it is heavy. The required properties of steel sheet for truck frame use are press formability and fatigue strength. Press formability can be optimized based on the previous investigation results. On the other hand, investigations on fatigue strength are relatively few, and the value of fatigue strength is not sufficient. Accordingly, the fatigue strength of high-strength steel sheet for truck frame use was investigated in this study. As for fatigue strength, the fatigue strength of steel sheet with scale is significant because the steel sheet is painted without pickling to remove the surface scale.

Vibration Damping Steel Sheet (VDS), which is composed of two steel-sheet skin layers and a middle layer of viscoelastic polymer resin, has been applied to automotive parts. For application to body panels, VDS needs several superior characteristics, such as, high damping capacity at room temperature and spot weldability as well as press formability. VDS developed by sandwiching a thermosetting resin has the loss factor of 0.2 at room temperature, and can be press formed and spotwelded under the same conditions as for an conventional steel sheet.

The formability of electrodeposited Zn-SiO2 composite coating has been studied. Flaking of the coating and die pick-up were hardly observed during the draw bead simulation test. Powdering resistance of the coating were also better than that of galvannealed steel. Good formability of Zn-SiO2 composite coatings is attributed, primarily to the low friction coefficient of the coating, and secondly to the microcracking effect which release the forming stress.

This paper presents the results of experimental analysis on the structural performance of steel, aluminum alloy and stampable sheets for bumper beams and the calculation results on the weight reduction of those bumper beams. Bending tests of straight beams, which were made of the three kinds of materials, were carried out in order to examine their structural performance. In consideration of failure modes, it was found that the maximum load and the absorbed energy of those beams can be evaluated by their material strength, their side-wall thickness and the height of their cross sections. Based on this evaluation method, the weight and the absorbed energy of the constant displacement were calculated using a common cross section. The weight reduction of aluminum alloy and stampable sheets is superior to 590MPa high tensile strength steel sheets.