Effect of Strain Rate Investigation on Forming Limit Diagram of Al-Cu Two-Layer Sheet

The use of two-layer sheets to improve mechanical properties such as ductility and strength and to improve chemical properties such as corrosion resistance has led to an increasing number of such materials in the industry. In this study, the formability of aluminum-copper two-layer sheets at a high strain rates is investigated by electromagnetic forming method. The simulation of electromagnetic forming of the two-layer sheet was performed at high strain rate using Maxwell and Abaqus software. By making coil and die and using sheets with different geometries and grids on the sheets, the forming limit diagrams (FLD) was also extracted experimentally. The simulation results showed that the electromagnetic pressure applied on the sheet in CA lay-up was 19% higher than in AC lay-up. Using the second derivative of strain criterion, the FLD of aluminum-copper two-layer sheet was derived. The FLD of aluminum-copper two-layer sheet with an initial thickness of 0.5mm is 30% higher in the AC lay-up than in CA lay-up. The reason for this improvement is that in the AC lay-up the sheet with more ductility (copper) is in the outer layer and has greater resistance to tensile stress and necking. The outer layer with better ductility can improve the ductility of the two-layer sheet. The FLD of aluminum-copper two-layer sheets has improved 120% in right-hand side and 55% in left-hand side at high strain rates compared to static conditions. There is about a 6% differences between the simulation and experimental results for forming limit diagram.