In the extrusion of clad composite materials with different flow stresses are usually used. This causes an inhomogeneous material flow which can induce sleeve or core fracture. In the present study, the material flow during indirect extrusion of copperclad aluminum (CCA) rods was analyzed by means of experimental and numerical investigations throughout the process. In order to provide material models for the numerical analysis hot compression tests of the aluminum alloy EN AW-1080A and the copper alloy CW004A were carried out. The indirect extrusion was performed using a conical die with a semi die angle of 45 • and an extrusion ratio of 14.8:1. The container was heated to 330 • C, while billet, die, and ram were kept at room temperature. The extrusion trial was then modeled with the FEM based software DEFORM 2D. Cross sections were taken from the extruded rod and compared to the corresponding sections of the simulation with regard to the development of the equivalent copper cross section. As a result, the development of extrusion force and equivalent copper cross section could be clarified. The numerical investigations indicated a higher flow velocity for the aluminum core than for the copper sleeve at the bearing channel. Therefore, high tensile stresses and fractures of the copper sleeve were induced. Additionally, the validated numerical analysis made possible to determine the conditions for a successful co-extrusion of the analyzed CCA rod.
The backward rod extrusion of bimetallic aluminum-copper alloys at room temperature was investigated. The aluminum alloy EN AW-1080A and the copper alloy Cu-ETP were selected to prepare the core and sleeve of the billet respectively. The copper cross section was equivalent to 30% of the billet. Moreover, the billet was extruded applying a conic die angle of 90° and an extrusion ratio of 14:1. Experimental results demonstrated that the combination of grounding marks on the die surface and the application of graphite foil reduced drastically the friction between copper and the conic die. Thus, a uniform material flow of aluminum and copper through the bearing channel was observed during the steady state of the extrusion process. However multiple fractures of the copper sleeve occurred at the end of the process. The extrusion process was numerically simulated applying the FEM-based software Deform 2D in order to estimate the state variables and material flow. The die and punch temperature evolution, as well as the die extrusion force were recorded during the whole process to facilitate the validation of the numerical analysis.
In order to investigate the multi-variable friction phenomenon during aluminium and magnesium extrusion, tribological experiments with the alloys AA6060 and AZ31 against hot working steel 1.2344 were carried out. Using a new axial friction test, the effects of the normalized normal stress (1.5-6), the temperature (300 °C - 500 °C) and the relative sliding speed (0.1 - 50 mm/s) were investigated. The influence of each parameter on the friction behavior is analyzed, the friction results are depicted and a modified Tresca friction model is developed.
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