Heterogeneous plastic deformation of stainless steel‑copper composites during multi-step micro deep drawing: experiment and modeling

In the present study, laminated 316 L stainless steel - T2 copper composites (50 μm) were initially annealed at 800, 900 and 1000 °C for 5 min, respectively, to achieve diverse microstructural characteristics. Then the formability of stainless steel‑copper composites was investigated through numerical simulation and multi-step micro deep drawing (MMDD) tests, and the deformation law and forming mechanism during MMDD was analyzed. The finite element model, which incorporates material inhomogeneity and surface morphology, exhibits excellent consistency with the experiment results obtained from MMDD tests. The stainless steel‑copper composites annealed at 900 °C exhibit the best plasticity owing to the homogeneous and refined microstructure and texture structure in both stainless steel and copper matrixes, and the micro composite cup with specimen annealed at 900 °C exhibits a uniformly distributed and symmetrical height profile, uniform wall thickness as well as high drawing ratio and superior surface quality with the fewest wrinkles. Additionally, the formability of stainless steel‑copper composites during MMDD is significantly influenced by size effects, and the barrel-shaped micro composite cups manufactured by the second step of MMDD exhibit a considerably deteriorated forming quality compared with bowl-shaped products obtained by the first step of MMDD. The stainless steel exhibits uniform wall thickness distribution comparing to copper during MMDD, and the maximum thickening and the maximum thinning occur at the cup mouth region where the compressive stress is the highest and nose radius region where the tensile stress is the highest, respectively.