Material-based design of the extrusion of bimetallic tubes

Using finite element and polycrystalline plasticity modeling, we explore the influence of die design and material behavior on the extrusion of bimetallic tubes. Three distinctly different extrusion designs are introduced and evaluated based on a range of macroscopic and microstructural criteria: die and punch stress, interface roughness, peak forming loads, and strain and crystallographic texture heterogeneities across the tube thickness. We find that an extrusion die design proposed here that differs from the conventional one is better for reduction of peak forming load satisfying objectives of the traditional design. However, when the design is more constrained and considerations of strain and microstructural heterogeneities and gradients are made part of the design criteria, we show that one die design promotes such gradients while the other minimizes them. In all three designs, large disparities in flow stress and hardening rate (>3 times) lead to larger interfacial strain gradients. These findings provide basic die designs that can be used to evaluate the degree and locations of strain and texture gradients across the tube thickness.