Prediction of central bursting during axisymmetric cold extrusion of a metal alloy containing particles

A simple cell model based damage dependent yield surface is used to model the effect of void nucleation and growth in an aluminum alloy during an axisymmetric cold extrusion process. Material parameters for characterization of the yield surface are determined through a physically consistent micromechanical cell modeling technique. The model can account for the behavior of a void containing a particle under severe compressive processing conditions. The formation of distinct, equally spaced, arrowhead shaped ‘central burst’ defects is observed during simulation of the extrusion process. Application of the model to a two-stage rolling process is also briefly illustrated. Formation of central bursts during extrusion and edge cracking during rolling is explained in terms of the hydrostatic stress distribution and the related void growth. The affects of material hardening, surface friction and die geometry are examined in the case of extrusion. Correlation is found between the simulations and analytical and experimental results, confirming the suitability of the constitutive model.