First-principles virtual tensile and shear strength calculations have been performed on the Fe2Al5// Fe4Al13 and -AlFeSi// Fe4Al13 interfaces. The Fast Inertial Relaxation Engine (FIRE) algorithm is used for optimizing these complex Intermetallic Compound (IMC) interface structures. To characterize the virtual tensile strength, an extended generalized Universal Binding Energy Relation (UBER) was used to fit the energy-displacement data. The virtual tensile strength was evaluated with the Rigid Grain Shift (RGS) methodology without atomic relaxations during tensile displacement and with RGS+relaxation with atomic relaxations. All calculated values for IMC//IMC interfaces in this study are compared with pure Al//Fe and Al//IMCs  interfaces to identify the role of IMCs at aluminum-steel joints.