Cold extrusion of porous metallic materials
Marek Galanty Akademia Górniczo-Hutnicza, Wydział Metali Nieżelaznych, al. Mickiewicza 30, 30-059 Kraków
Annals 2 No. 4, 2002 pages 135-138
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abstract The well known advantages of P/M technology focus our attention also on manufacturing long products of complicated cross-section. The extrusion process is capable of producing such products, and additionally, due to the favourable state of stress in the deformation zone, the high degree of material consolidation can be obtained. This influences in a positive way the mechanical properties of the product. The two extrusion techniques are possible in practice. First one (Fig. 1a,b) is similar to the conventional extrusion of solid feedstock; it consists in forward or backward extrusion of compacted samples. The second case consists in extrusion of a loose powder (Fig. 1d) material poured directly into the extrusion container, in which the opening (die) is covered with a metallic disk. The loose powder pressed by the punch undergo densification, next pushes out the disk and flows out through the die in the form of a solid extrudate. The second technique can be performed only in a room temperature without using of binders, that are usually added to the metal powder to enhance it densification. In this case the decisive role play the adhesive forces between the powder particles. The attraction of this procedure is shortened way from the powder to finished product, by eliminating compaction and sintering from the processing route. The aim of this work was to perform the extensive experiments on the cold extrusion of compacts and loose metallic powders. Three selected fractions of technical purity (99.5 wt.%) atomised aluminium powder RAL1 of 0÷30, 110 and 450 µm were used to prepare compacts of different green density (Fig. 2) for cold extrusion (Figs 3-5). Additionally, the loose fraction of 450 µm was used directly in the extrusion. The extrusion was performed on a 3MN capacity vertical hydraulic press. The container of 35 mm in diameter was equipped with a dies having different opening diameter within the range of 16÷9 mm. Before filing the container the die opening was covered with aluminium disks of various thickness. Due to this fact the extrusion was initiated at different loads, so that, the powder in the container was consolidated prior to extrusion to different density. At the stable state of the extrusion the process was interrupted and the rest of the feedstock was taken out of the container. The rests were next submitted to hardness examination on their axial cross-section (Fig. 6) to determine the mode of the material flow within the container. The density and hardness at different locations of the extruded rods were also examined. The extrusion load in dependence on the ram displacement was recorded during experiments (Figs 3, 7). The samples from different locations of the extrudate were submitted to mechanical testing. The obtained results enabled to determine the influence of the extrusion mode on the load required, on the material flow and on the distribution of mechanical properties along the extrudate length.