EVOLUTION OF THERMO-MECHANICAL FIELDS IN HOT HOLLOW EXTRUSION OF ALUMINUM: A COMPUTATIONAL STUDY VALIDATED BY EXPERIMENTS

During the last decade it has become common practice to employ the finite element method (FEM) in the study and optimization of metal forming processes [1]. Metal forming processes are governed by non-linear momentum and heat transfer equations which are closely coupled. As a result, it is of cardinal importance that the FE models are both verified and validated.

In the current study the process of hot extrusion of a hollow Al 1050 billet was investigated by finite element analysis (FEA) in conjunction with hot extrusion experiments. First, the material plastic flow stress manifolds were determined using cylindrical billet upsetting experiments in conjunction with FEA. The Zener-Holloman (ZH) parameter, which can be correlated to microstructure evolution [2], was determined and its spatial distribution as a function of local strain rate and temperature was computed using the FE model. Second, the material flow stress manifolds determined in the first stage of the study were applied in a coupled finite element model developed for the study of hot hollow extrusion. The FE model was used to examine the influence of initial billet temperature, die opening angle, ram velocity and friction between tools and billet on the deformation process and resulting ZH distribution. Metallographic characerization of the extruded aluminum tubes was used to further examine the relation between the time dependent thermo-mechanical fields and changes in material grain size and texture.

References:

[1] Diter, G.E. Mechanical Metallurgy. McGraw-Hill 1981.

[2] Guzel, A. Jager, A. Parvizian, F. Lambers, H. G. Tekkaya, A.E. Svendsen, B. Maier, H.J. "A new method for determining dynamic grain structure evolution during hot aluminum extrusion", Journal of Materials Processing Technology 212, (2012) 323-330.