Analysis of the cracks formation on surface of extruded magnesium rod based on numerical modeling and experimental verification

To reduce the surface cracks of extrusion rod for AZ31 magnesium caused by nonhomogeneous metal flow in extrusion process, 3D computer finite element (FE) simulations of extruding a wrought magnesium alloy AZ31 into rods have been performed and the results have been verified in extrusion experiments under identical conditions. The tendency to generate the dead zone is decreased by employing the die angle 60 degrees at the cone-shaped die comparing with the die angle 180 degrees. The surface additional tensile stresses of the rod at the die exit are decreased greatly so that the surface cracks caused are avoided by using the die angle 60 degrees. The extrusion die with die angle 180 degrees would increase the higher temperature rise and possibility of crack formation on the rod surface that caused by die angle 60 degrees and temperature rise decrease tensile strength of the AZ31 rod. The experimental results show that die angle 180 degrees could cause continuous cracks on the surface of the extruded rod. The extrusion force required is reduced approximately 15 ton by employing the die angle 60 degrees. Theoretical results obtained by the Deform (TM)-3D simulation agreed well with the experiments. The obtained results provide the fundamental and also practical guidelines for the design and correction of dies to produce magnesium rod with good surface quality.