Analysis of Forming Limits During Cold Forging of Aluminum Hybrid Billets

Metal forming processes for manufacture of hybrid components with complex geometry is one of the most promising trends in materials science. At the same time, such processes pose serious challenges regarding the interface properties between the different materials. Thus far, models are existing to describe cold welding of hybrid components and their plasticity during following deformation processes. However, these models have been developed and validated mainly for processes, where stress and strain states are recognized as simple (e.g., drawing, roll bonding). In this contribution, a flange upsetting process using hybrid billets made of AA-6060 and AA-7075 is subjected, where the deformation conditions significantly differ (non-monotonous and complex strain history). The main aim of this paper is to investigate such process with special emphasis on acting stress conditions in the interface with respect to delamination effects occurring during cold forging experiments. Also, the influence of an initial bond between the aluminum components, created by compound hot extrusion, is investigated both experimentally and numerically. In this context, three geometrical models of the hybrid billet (variation of diameter and wall thickness of the reinforcing component) were used. Analyses show that even if bonding in extrusion process is not ideal and depends on various influencing parameters, it makes subsequent cold forging process more stable and reliable regarding material flow compared to billets without initial bond.