Metallographic Determination of Strain Distribution in Cold Extruded Aluminum Gear-Like Element

Abstract

In this study, an experimental, metallographic method for determining strain distribution in a cold extruded aluminum gear-like element, based on the dependence of recrystallized grain size on prior deformation, was devised in order to overcome design problems in manufacturing of complex parts where critical values of strain and stress could cause a fracture. The method was applied on a 99.5% aluminum bar subjected to cold, radial extrusion, in order to produce complex gear-like element. To reveal the strain and stress distribution in specimens, the calibration and flow curves were first obtained by uniaxial compression (Rastegaev test). Afterwards, the grain size in different parts of the gear section was examined, the strain and stress distributions were calculated, and the results were confirmed by microhardness measurements. It was found that grain size, strain, stress, and microhardness considerably differed throughout the cross-section of the gear. The coarsest grain, and thus the lowest strain zone, was obtained in the central part of the tooth and in the zone between teeth. Conversely, the finest grains appeared in the highest strain zone at the specimen surface, particularly in the root of the teeth. Furthermore, results were supported by microhardness measurements, i.e., microhardness corresponded to grain size and strain hardening. Finally, the real view of material flow in the complex extruded part was successfully obtained by the metallographic method.