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

研究了两层复合金属（SUS430/A1）和三层复合金属（SUS430/A1/SUS304）在400oc条件下双向拉伸和拉伸弯曲/不弯曲过程中的变形特性和压成形性能。还讨论了冷轧粘接SUS304/A1复合板在拉伸弯曲/不弯曲过程中的分层现象。结果总结如下：(1)实验确定了复合金属板及其零部件（SUS304、SUS430和A1）的成形极限图。SUS430/A1和SUS430/A1/SUS304复合板材与SUS430预轧板材相比具有更高的成形性能。(2)基于Hill的局部缩颈理论，导出了复合板在正应变比下的成形极限。理论预测的FLD与实验结果比较吻合。(3)复合板负应变比下的成形极限可以用考虑孔洞生长的板厚缺陷发展模型（修正M-K理论+孔洞生长）来解释。(4)从理论和实验两方面研究了复合板在模角拉伸弯曲/不弯曲过程中板料厚度的变化。阐明了层合板几何形状（包层比）、模具半径和拉伸力对板厚变化的影响。(5)研究了冷轧SUS430/A1板在拉伸弯曲/不弯曲过程中在模具拐角处的分层现象。当模具半径较小，拉伸力较大时，容易发生分层。通过对拉伸弯曲/伸直过程的数值模拟发现，伸直过程中作用于复合材料层合边界上的法向应力和剪应力对分层的影响很大。

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.