Papers by Keyword: Hydrostatic Extrusion (HE)

Abstract: The aim of this study was to investigate the homogeneity of the bulk nanocrystalline titanium rods obtained by Hydrostatic Extrusion (HE). The investigated material was commercially pure titanium grade 2. The final products of extrusion were nanocrystalline rods with diameters of 7 and 10 mm and lengths of about 250 mm. The size and shape of the grains were examined on transverse sections using transmission electron microscopy (TEM). The grain size was determined by the average grain equivalent diameter d2. The grain size diversity was quantified in terms of the equivalent diameter coefficient of variation CV (d2). The samples for the microscopic analyses were cut from various regions of the rods i.e. top, end, centre, and from surface of the rods. In all the samples, the average grain size determined on transverse sections was about 70 nm and the nano-grains in the various regions of the rods were similar in the shape. The examinations demonstrated that the nanostructure of the extruded rods was homogeneous. This observation was confirmed by the results of microhardness measurements.

Abstract: The aim of the work was to optimise the Hydrostatic Extrusion, HE, parameters in terms of their influence on the microstructure and certain mechanical properties of 6082 aluminium alloy. The investigations focused on the fabrication of a nano- or ultrafine-grained microstructure of the alloy. The effects of a multi-pass process were compared with those of a one-pass process producing the same cumulated true strain of 3.75. Both the multi-pass and the one-pass deformation resulted in profound grain refinement of the alloy. The microstructure contained grains with an average size of 195 nm and 239 nm, respectively. The grain refinement brought about a significant improvement in the microhardness and tensile strength of the alloy. It should be noted that the multi-pass HE produced slightly greater improvement than the single pass process.

Abstract: Titanium was subjected to hydrostatic extrusion, a method of producing Severe Plastic Deformation (SPD). The experiments were aimed at refining the microstructure of the titanium in order to improve some of its mechanical properties. The effect of the initial state of titanium on the process of extrusion process and the final product was investigated. The results of these investigations are used to establish the optimum conditions for the hydrostatic extrusion process and more easily selecting the initial condition of the material according to the intended application of the extruded product.

Abstract: Samples of 316LVM stainless steels were hydrostatically extruded in a multi-step process to a total true strain of 1,84 and subsequently annealed at different temperatures. The structural changes occurring as a result of HE and annealing were observed using a transmission electron microscope. The microhardness of the samples was measured using a load of 200g. The results show that hydrostatic extrusion results in a uniform microstructure characterized by a high density of nano-twins. Subsequent annealing at 600°C produces a partial transformation to a nano structure of average grain size 54 nm. At an annealing temperature of 700°C a fullyrecrystallized uniform microstructure consisting of 68 nm diameter nano-grains was formed. It should be noted that 700°C is much lower than that required to recrystallize a micro-grained alloy of the same composition. The microstructural changes which occurred during annealing have a significant effect on the mechanical properties. The microhardness after HE increased following annealing at 500°C. However, annealing at 800°C resulted in a drop in microhardness, indicating the occurrence of grain growth.

Abstract: Recrystallization and grain growth were studied in an austenitic stainless steel 316LVM processed by hydrostatic extrusion (HE) to a total true strain of 2. HE processing produces in this material the microstructure which consists of nanoscale twins on average 19 nm in width and 168 nm in length. The samples after HE were annealed at various temperatures for 1 hour. The structural changes were investigated using TEM. The heat induced changes in nanotwinned austenitic steel are significantly different when compared to the ones in a conventionally deformed material. Microstructural changes take place at lower annealing temperature. Annealing at 600°C brings about a partial a nanostructure reorganization into nanograin of average size 54 nm. An uniform microstructure with nanograins of 68 nm in equivalent diameter was obtained after annealing at 700°C whereas conventional 316LVM steel fully recrystallizes after annealing at 900°C for 1h. Annealing at higher temperatures results in grain growth.

Abstract: The potential application range of coarse-grained commercial purity titanium is limited by its low mechanical properties. A reduction of the grain size of titanium leads to a significant increase in its strength and hardness. This paper is concerned with application of hydrostatic extrusion (HE) for fabrication nano-grained titanium. In the present study titanium rods were subjected to hydrostatic extrusion with the aim to reduce the grain size to the nano-metric scale and thereby improve the mechanical properties. The obtained material can be an equivalent and compete with the commonly used Ti6Al4V alloy. The results were compared with those other SPD techniques reported in the literature and refered to Hall-Petch relationship.

Abstract: In this study particle redistribution and grain size refinement induced by hydrostatic extrusion (HE) have been studied in two Al-Si cast alloys (Al-9%Si and Al-11%Si). It has been found that HE results in a significant changes in particle shape, size and distribution which was revealed by SEM observations and quantified using stereological parameters. At the same time, significant grain refinement down to ~100 nm in diameter takes place in aluminium phase. Such a microstructure evolution affects substantially the mechanical properties of two-phase alloys. The yield strength and tensile strength increase over two times whereas the plasticity only slightly decreases.

Abstract: A bimetal composite material is a variant of the typical composite that is composed of two materials joined at their interface surface. The advantage of clad material is that the combination of different properties of materials can satisfy both the need of good mechanical properties and the demand of user such as electrical properties simultaneously. This paper is concerned with the hydrostatic extrusion process of copper-clad aluminum rod. The commercially available finite element program ANSYS was used to simulate the process of hydrostatic extrusion for Cu/Al bimetal composite through the equal-strain contour concave dies. The relative slippage between the inner and outer metals under the condition of different friction factors is studied, and the stress-strain distribution in the billet was analyzed. Experiment test was carried out; it was found that the experimental result has good agreement with relative slippage from the finite element analysis.

Abstract: Deformation characteristics and forming limit of ultrafine-grained bulk Al-Mg alloy were examined with upsetting process. The Al-7.5%Mg alloy produced by cryogenic milling and HIP was subjected to hot hydrostatic extrusion as a final consolidation in fabricating the ultrafine-grained bulk material. Upsetting was performed to study their mechanical characteristics in a practical forming process. The extruded specimen showed that the pores remained in spite of the HIP had been collapsed and almost eliminated. The effective removal of the distributed pores resulted in significant increase of formability by preventing early cracking. Metallographic investigations showed that the size of grain remained below a few hundred nanometer scale in the processes.

Abstract: Multi-filament fabrication process using repetitive hydrostatic extrusion of Cu/Al at high temperature was conducted to obtain micro-scaled Aluminum wires. In the process an aluminum rod claded with a copper tube was extruded repetitively three times where a number of the single extruded rods were bundled together and subjected to hydrostatic extrusion to obtain multi-filament wire bundle. Aafter final bundle extrusion the diameter of the aluminum rod was effectively reduced from 33.6 mm to 30μm.