In magnetic pulse welding, the deformation phenomenon of a moving sheet is divided into the deformation and continuous collision processes, then, the deformation analysis of the sheet is performed by using a magnetic pressure delivered to the sheet. When applying the pressure provided by neglecting an electric field generated during the deformation of the sheet, the calculated values accord only with one point for many measured values of both deformation height and deformation velocity, and errors greatly increase as the calculated values deviate from the point according. The new magnetic pressure corrected using a pressure drop coefficient is introduced because the deforming sheet leads to a drop in the pressure. If a successive approximation is applied to the deformation analysis, many calculated values approach the standard measured values. The calculated values are within a small error range for the measured values at 17 out of 18 points. It has been clarified that the deformation of the moving sheet is estimated fairly accurately by using the successive approximation.

To improve the press formability of aluminum alloy sheets, method using partially softened blanks, such as tailored heat-treated blanks method, have been investigated, in which aluminum alloy sheets whose strength has been distributed are formed. In square-cup forming, it is known that the softening corner flanges improves drawability, but it was not clear which region of the blank should be softened to improve drawability. In this study, the optimal region to be softened for the deep drawing of a square cup was investigated by experimental and numerical analyses. The A6061-T6 sheets were locally solution-treated and softened. Then, square-cup drawing tests were performed. Six types of softened region were prepared to investigate the effects of the distance from the center to the boundary of the softened region at the corner and of the softened region ratio in straight sections. In the blank with the widest softened region in straight sections, the shrinkage deformation of the corner flange was suppressed. Therefore, there was an appropriate range for the softened region ratios of straight sections and corners. The formability of blanks with appropriate softened regions was improved by 1.2 times compared with that of T6 sheets. In addition, a similar optimal value was obtained by optimization by numerical analysis.

The combination of the hydromechanical deep drawing method and the partially softened blank method was investigated to improve the press formability of aluminum alloy sheets. The strength distribution was previously endowed to an aluminum alloy sheet by partial heat treatment, and then the deep drawing was performed by applying hydraulic pressure against the punch during forming. This combined method was applied to the deep drawing of square cups of A6061 sheets and forming tests were conducted on circular blanks of various diameters to investigate the forming limits. While the conventional deep drawing method could form blanks up to 70 mm in diameter, a diameter of up to 90 mm could be achieved by the hydromechanical deep drawing with partially softened blanks. The effect of the partially softened region on the formability was investigated to clarify the optimal region for forming the maximum diameter. The effect of the hydraulic pressure in the hydromechanical deep drawing process was also investigated. The forming limit was improved by increasing the hydraulic pressure, and when the hydraulic pressure was 20 MPa, it was possible to form a blank of 100 mm. The mechanism for improving formability was clarified by studying the punch load force and thickness distribution.

A claying method for lubrication has been developed to reduce the environmental load when an aluminum workpiece is lubricated for cold forging. In this study, the claying method and the clayed lubricant are investigated. Claying produces a layered double hydroxide on the aluminum workpiece. It normally takes about 120 minutes to produce the clay film on the aluminum workpiece. A prior alkaline treatment of short duration before lubrication enables the claying reduction in claying time, so that the time to produce the clay film takes 2en10 min in the claying method. The clay lubricant resulted in less friction. Using the clay-lubricated workpiece, the ring compression test showed a Coulomb’s frictional coefficient m of 0.061, which is lower than m = 0.13 when using the conventional lubricant of aluminum-fluoride and zinc. Moreover, using another claylubricated workpiece, punch loads were reduced in 70-shot continuous backward-cup extrusion tests. Extrusion conditions included the cup depth/punch diameter ratio of 5.26, and an 81% reduction in cross-sectional area. All extruded cups showed a smooth inner surface without galling. It was found that the claying method is effective for lubricating aluminum for cold forging.

In the process of a tube, a phenomenon called "thickness deviation" occurs, in which wall thinning occurs on the tensile side and the wall thickening occurs on the compressive side. The reduction in wall thickness on the tensile side may result in a loss of strength. Defective phenomena in bending include wrinkling and flattening, and research has been conducted on methods to suppress these phenomena. However, there have been few studies on the suppression of wall thinning. The purpose of this study is to improve the uniformity of wall thickness in the cross section of square tubes after bending. We investigated the effects of the preprocessing cross-sectional shapes of strip and square tubes on wall thickness after bending and examined the cross-sectional shapes that should result in uniform wall thickness after processing.

Tailor welded blanks (TWBs) are considered a suitable method to achieve the light-weighting of automobiles efficiently, and the use of dissimilar metal TWBs may further enhance the effect. To produce steel/aluminum alloy TWBs with high weld strength, friction stir welding is useful, and previous research has revealed that an artificial re-aging treatment after welding further increased the weld strength. However, galvanic corrosion would cause the depression of reliability for such TWBs. In this study, the combined cycle corrosion test was conducted for SPCC/A6061P-T6 joined by friction stir welding. Before the corrosion test, the effect of the artificial re-aging treatment after welding was preliminarily investigated. From experimental results, it was confirmed that these treatments enhanced weld strength by 20-30%. After that, the combined cycle corrosion test was conducted for as-welded and treated SPCC/A6061P-T6 TWBs. As a result, we found that almost no change occurred in weld strength until around the 20th cycle, and after that, the weld strength decreased moderately. Beyond the 30th cycle, weld strength decreased rapidly and practically disappeared around the 40th cycle for as-welded blanks and around the 50th cycle for treated blanks. From the results of observation using FE-SEM and EDS analysis, the mechanism of the decrease in weld strength was clarified.