Lüders effect in Al 99.7% extruded via the KoBo method

Abstract

Abstract The aim was to determine the effect of extrusion process parameters of the KoBo method (initial billet temperature, extrusion rate and die oscillation frequency) on the Lüders phenomenon occurrence in aluminum wires. The material used in the experiment was 99.7% pure Al billet. The extrusion was carried out with the following parameters: extrusion ratio λ = 100, initial billet temperature in the range of 293–493 K, extrusion rate of 0.1–0.5 mm · s−1 and frequencies of 3, 5 and 8 Hz (the die oscillation angle was a constant ± 8°). Output materials were mechanically tested and examined microscopically. Based on the results it was found that: the Lüders phenomenon in aluminum wires extruded by the KoBo method appears only i) in a specific range of the extrusion force, namely 450–650 kN, ii) a specific range of, yielding strength (100–140 MPa), iii) dependent on the combination of process parameters its extent and position can vary over a product's length, iv) tests have also shown that this phenomenon has a continuous propagation nature only at the initial stage of the tensile test.