J. Richert

Work hardening and microstructure of AlMg5 after severe plastic deformation by cyclic extrusion and compression

Deformation by cyclic extrusion/compression in AlMg5 leads to the same stages of work hardening as unidirectional deformation. The analogy is confirmed by studies of the microstructure, by analysis of long range internal stresses and by evaluation of dislocation densities. The strains leading to the various stages of work hardening are much higher than those in conventional deformation modes while the dislocation densities in the stages are about the same. The strain shift in cyclic extrusion/compression is attributed to the reversal of strain path. The resulting subgrain size is smaller than that resulting from conventional deformation modes which seems to be a consequence of the higher hydrostatic pressure of cyclic extrusion/compression.

Characteristic features of microstructure of ALMg5 deformed to large plastic strains

Abstract The evolution of the microstructure of the AlMg5 alloy was analysed and its typical features were determined. Large degrees of deformation were achieved using the cyclic extrusion compression method. The microstructure was analysed by transmission electron microscopy and scanning electron microscopy. Dense dislocation walls and microbands cutting randomly distributed tangles of dislocations, were observed. After a true strain ϕ =16, mutual crossing of microbands led to a ‘subgrain like’ microstructure. Large disorientation angles up to 60° were found between some neighbouring ‘subgrains’, but generally angles were lower (below 15°).

Effect of large deformations on the microstructure of aluminium alloys

Abstract AlMg5 and AlCu4Zr alloys have been deformed in the range of true deformations ϕ=0.4–13.9 using the cyclic extrusion compression (CEC) method. In the entire range of the examined deformations a strong tendency to form microbands in the dislocation structure of the alloys has been observed. In the area of the microbands a strong misorientation of 60° occurred. Characteristic changes appearing as a result of the intersection of the microbands, leading to the formation of subgrain microstructure, have been observed. Similarly as in the microbands, large misorientation angles between the newly formed subgrains occurred. The nanometric dimensions of the newly formed subgrains and large misorientations angles in the alloys, plastically deformed above the conventional deformation range, indicated the tendency to form a microstructure typical for metallic nanomaterials.

Microband formation in cyclic extrusion compression of aluminum

Abstract The influence of very large deformations on the properties and microstructures of Al99.95 and Al99.992 is investigated. The very large deformations are imposed by the cyclic extrusion-compression (CEC) method, which combines extrusion and compression processes. It is found that above true strains of 4 and 8 respectively, the compression proof stresses of Al99.992 and Al99.95 stabilize. The property stabilization appears to result from the increasing incidence of microbands which leads to the final constancy of the microstructure parameters. The homogeneous chess-board like microstructure forms during the deformation by the CEC method, as the result of rearrangement of microstructure by the mutually crossing microbands leading to the final dominance of persistent macro shear bands.

Physical modeling pertaining to extrusion of asymmetric shapes

This study investigates the influence of weld cavity geometry on metal flow during the extrusion process. The results of physical modeling done with lead billets are presented. A method of weld cavity design that ensures uniform metal flow in extrusion of asymmetric shapes is proposed.

Ag Powders Consolidated by Reciprocating Extrusion (CEC)

CEC has unique characteristic. These are applicability of very large strain and deformation under high hydrostatic pressure. Due to these abilities of CEC, several unique phenomena have been observed. One of them is the possibility of consolidation of metallic powders in room temperature to the form of bulk material. In the present paper the consolidation of AgSnBi and AgNi to bulk composites was presented. Applying the deformation of  = 0.42 in the single cycle of CEC, under high hydrostatic pressure, the samples without pores and discontinuities were fabricated. The microstructure observations were performed by optical microscopy (MO), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). They show refinement of microstructure at all levels of observation. The nanometric-size subgrains/grains were found inside consolidated granules. The microhardness level of AgSnBi in average achieved level 110 μHV100, and AgNi of about 90 μHV100. The AgSnBi samples consolidated by CEC and additional hydrostatically extruded to wires with 3 mm in diameter average showed 500 MPa yield point.

Numerical Analysis of Aluminum Alloys Extrusion through Porthole Dies

In the work the distribution of stresses and strains as well as temperature field within the welding chamber of the porthole die were determined. The analysis was performed by the use of the computer program DEFORM based on a finite element method. The direct hot extrusion of 2024 aluminum alloy was investigated with the use of the porthole dies of different geometry. Particularly, a different height of the welding chamber was adopted in calculations. The calculations allowed determining both pressure and temperature levels and their distributions within the welding chamber leading to the best welding conditions for the alloy tested.

Bulk Nanomaterials and Powders Consolidation Produced by Cyclic Extrusion Compression

The Cyclic Extrusion – Compression - reciprocating extrusion process (CEC) is one of severe plastic deformation methods (SPD), which allow to produce bulk nanomaterials without changing the initial shape of deformed samples. The results are presented showing that the average grains size and microbands thickness in aluminium alloys decrease below 100 nm. The investigations revealed that the average grains size is about 250 nm and 200 nm in polycrystalline and monocrystalline copper, respectively.The Cyclic Extrusion Compression method is also used to produce bulk materials by powder consolidation. The subgrains/nanograins inside the silver powder particles after the consolidation processes achieved the mean size of about 100 nm. Moreover, it has been found that inside structure observed by TEM, the consolidated powder granules consisted from nanometric twins of about 10 – 20 nm. This silver based powder consolidated by CEC method were extruded by hydrostatic extrusion method. The final product were the wires with a diameter of 3 mm, which were used to electrical contacts production.

Microstructure of AgNi and AgSnBi Powders Consolidated by CEC

Powder metallurgy is widely used to the production of AgNi and AgSnBi powders employed for electrical contacts. In the work AgNi and AgSnBi powders were consolidated by the cyclic extrusion compression (CEC) method enabling cyclic unlimited deformation. In the initial stage the AgNi powder contained the two phases Ag and Ni, recognized by the EDX technique using scanning electron microscopy (SEM). The investigations shown that the Ni phase is distributed in the form of small granules around larger Ag granules. In the AgSnBi powder phases Ag + Bi + Ag3Sn (ξ) were distributed uniformly. It was found that after the CEC consolidation phases were excellently joined without cavities and cracks. Detailed observations of microstructure have been performed by the transmission electron microscopy (TEM) and revealed inside the consolidated granules nanometric grains with the nanometric twins inside.