Deformation Characteristics and Press-Formability of Steel/Aluminium Clad Sheet Metals

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Deformation characteristics and press-formability in biaxial stretching and stretch bending/unbending were investigated for warn-roll-bounded (at 400ﾟC) two-ply (SUS430/A1) and three-ply (SUS430/A1/SUS304) clad sheet metals. Delamination during stretch bending/unbending was also discussed for cold-roll-bonded SUS304/A1 clad sheet metals. The results are summarized as follows.(1) The forming limit diagrams (FLD) for the clad sheet metals and their components (SUS304, SUS430 and A1) were experimentally determined. The clad sheet metals of SUS430/A1 and SUS430/A1/SUS304 have higher formability compared with the warn-rolled SUS430 sheet.(2) The forming limit in the positive strain ratio for clad sheet metals has been derived based on Hill's localized necking concept. The predicted FLD by the theory agrees comparativery well with the experimental one.(3) The forming limit in the negative strain ratio for clad sheet metals can be explained by a model of the progress of sheet-thickness imperfection with consideration of void growth (modified M-K theory + void growth).(4) The sheet-thickness change during stretch bending/unbending around a die corner was examined both experimentally and theoretically for the clad sheet metals. The effects of laminate geometry (clad ratio), a die radius and stretching force on the sheet-thickness change have been clarified.(5) Delamination during stretch bending/unbending around a die corner was investigated for a cold-roll-boned SUS430/A1 sheet. Delamination likely occurs when a die radius is smaller and the stretching force is larger. It was found from the numerical simulation of the stretch bending/unbending that the delamination is strongly affected by the normal and shear stresses acting on the laminate boundary of a clad sheet during unbending process.