Effect of Die Bearing Geometry on Extrudability of High-Strength AA6082 Alloy with Cu

Abstract

This study investigated the impact of die bearing geometry on the surface cracking behavior, of a high strength AA6xxx alloy. Experimental and numerical methods were employed, along with differential scanning calorimetry tests to determine the material’s solidus temperature. Four different die geometries were employed in both the extrusion trial and the simulation. Extrusion trials were conducted for each die geometry over a range of extrusion speeds with the resulting surface defects being examined using SEM. The findings indicate that die bearing geometry significantly affects surface morphology and crack occurrence. Choked dies enabled crack-free extrusion at higher speeds, particularly a 12 mm choked bearing with a 1° angle, outperforming a 25 mm flat bearing and zero-bearing die. The 35 mm choked bearing achieved crack-free extrusion even at maximum extrusion speed, yielding smoother surfaces than the other dies. Numerical simulations demonstrated the differences in stress states using different die bearing geometries, showing that the choked bearings alter the stress state at the die corner to cause a transition from high tensile stress to lower tensile or compressive stress. The extrusion limit diagrams for different die bearings were also constructed based on the extrusion trial data to provide guidance for choosing appropriate extrusion parameters for future studies. This study adds a valuable contribution to the existing literature by shedding light on the role of die bearing geometry in controlling surface morphology and surface crack formation, providing important insights that can be used to optimize the extrusion process.