Structure and mechanical properties of AlMg4.5 and AlMg4.5Mn wires extruded by KoBo method

Abstract

The influence of the number of extrusion steps in KoBo method (at the same total extrusion ratio of λ = 100) on structure, mechanical properties and work hardening characteristics of AlMg4.5 and AlMg4.5Mn (AA5083) alloys was investigated. It was found that one-step extrusion leads to the formation of recrystallised structure of the material, while the use of two-step extrusion yields a fibrous structure of a "mixed" type, i.e. containing areas where the intensive recovery effects are associated with partially recrystallised structure. As a consequence, the strength properties of the latter extrudate are much higher in both as extruded state and after the subsequent cold rolling. In all cases, the tensile stress-strain curves of the extrudates show the flow stress serrations that are typical for the Portevin - LeChatelier (P-L) effect. In a few tensile tests, the P-L effect was preceded by the plastic flow instability being typical for the occurrence of Lüders bands. Both AlMg4.5 and AlMg4.5Mn extruded wires show a monotonic increase of the work hardening that results from the following cold deformation in the groove rolling.