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Monolithic copper honeycombs were fabricated by a plasticizing powder extruding-sintering technology. The effect of sintering conditions on volume shrinkage, apparent density, microstructure, mechanical properties and heat conductivity of copper honeycombs were studied. With increasing sintering temperature and time, the metal particles form sintering necks and gradually coalesces into grains, and volume shrinkage, apparent density and strength increase, and the optimum sintering parameters are 950 °C for 2 h. When sintering temperature rises from 800 to 1000 °C, the volume shrinkage ranges from 15 to 30%, and the apparent density ranges from 1.49 to 1.74 g/cm3. When sintering time increases from 1 to 2.5 h, the volume shrinkage ranges from 18 to 27%, and the apparent density ranges from 1.52 to 1.70 g/cm3. Under axial compression, the yield strength ranges from 7.2 to 20.4 MPa. Under radial compression, the yield strength ranges from 2.1 to 3.5 MPa. The longitudinal and transverse effective thermal conductivity of monolithic copper honeycomb was calculated by parallel and series models, respectively. The maximum longitudinal effective thermal conductivity of copper honeycomb is 50.26 W/(m K) and the maximum transverse effective thermal conductivity is 0.033 W/(m K), which indicates that the longitudinal heat transfer of copper honeycomb is much better than transverse. It can be designed as heat sinks by using the performance of longitudinal thermal conductivity of copper honeycombs. [ABSTRACT FROM AUTHOR]

Microstructure uniformity and grain refining efficiency of Al-5Ti-1B alloy rod prepared by powder extruded process and continuous casting and rolling process are investigated in detail by X ray diffractometer, scanning electron microscope and electron probe. It is found that TiB2 and TiAl3 particles are uniformly distributed in the powder extruded Al-5Ti-1B alloy via gas atomization and hot extrusion process. The samples with 0.2% powder extruded Al-5Ti-1B alloy rod holding for 2 min consist of equiaxed grains with an average diameter of 183 µm. Even the holding time extended to 180 min, the average diameter is still stable (229 µm). Al-5Ti-1B alloy rod prepared by the powder extruded process presents better grain refinement and stronger resistance to grain coarsening. [ABSTRACT FROM AUTHOR]

In this study, mechanical properties and microstructures of extruded aluminum matrix composites were investigated. The composite materials were manufactured by two step methods: powder metallurgy (mixture of aluminum powder and carbon fiber using a turbular mixer, pressing of mixed aluminum powder and carbon fiber using a cold isostatic pressing) and hot extrusion of pressed aluminum powder and carbon fiber. For the mixing of Al powder and carbon fibers, aluminum powder was used as a powder with an average particle size of 30 micrometer and the addition of the carbon fibers was 50% of volume. In order to make mixing easier, it was mixed under an optimal condition of turbular mixer with a rotational speed of 60 rpm and time of 1800s. The process of the hot-extrusion was heated at 450°C for 1 hour. Then, it was hot-extruded with a condition of extrusion ratio of 19 and ram speed of 2 mm/s. The microstructural analysis of extruded aluminum matrix composites bars and semi-solid casted alloys were carried out with the optical microscope, scanning electron microscope and X-ray diffraction. Its mechanical properties were evaluated by Vickers hardness and tensile test.

Abstract In this paper, 2.5 vol% TiBw/TA15 composites were fabricated by low-energy milling and subsequent powder extrusion. After low-energy milling process, the fine TiB 2 powders were adhered on the surface of the spherical TA15 powders. Next, the blended powders were extruded at 1100 °C with extrusion ratio of 10:1. The Widmanstatten α + β microstructure with thickness of 550–620 nm in α phase was obtained and the strong (0001) α //ED and (101) α //ED texture was formed after powder extrusion. The TiB whiskers (TiBw) twisted along the extrusion direction and led to the 'wall' structure. High-temperature tensile behavior of this studied composites was investigated at 800–950 °C with strain rate of 0.001–0.1 s−1. According to the stress-strain curves, the activation energy (Q) was calculated to be 325 kJ mol−1, higher than the TA15 matrix, which is due to the combined effect of phase morphology, extrusion texture and TiBw reinforcements. In addition, the tensile strain has effect on microstructure evolution. Static spheroidizing has been processed in the grip area of tensile sample. As the tensile strain increased, the volume fraction of and the average grain size α phase decreased. Moreover, voids nearby the TiBw reinforcements were observed due to the incoordination deformation between TiBw and TA15 matrix. [ABSTRACT FROM AUTHOR]

The flow behaviour of Al–SiC nanocomposites prepared by mechanical milling and hot powder extrusion methods was studied at different temperatures (350–500°C) and strain rates (0.005–0.5 s−1). The flow of the Powder metallurgy nanocomposites exhibited a peak stress followed by a dynamic flow softening behaviour. It was shown that mechanical milling increased high-temperature strain rate sensitivity of ultrafine-grained (UFG) aluminium while decreasing its flow dependence to temperature. Constitutive analysis of the hot deformation process by Zener–Hollomon parameter (Z) also indicated a remarkable increase in the deformation activation energy (about 40%). Likewise, SiC nanoparticles (up to 2vol.-%) were shown to contribute in the high-temperature strengthening of UFG aluminium with a significant effect on its thermal stability. The findings were explained based on the pinning effect of hard nanoparticles on grain boundaries and mobile dislocations as well as microstructure stabilisation at elevated temperatures. [ABSTRACT FROM PUBLISHER]

A powder extrusion pr°Cess based on the superplastic behavior of Zn-22wt%Al eutectoid alloy is proposed as a means to achieve fine microstructures in the manufacture of miniature hollow helical gears by reducing the forming load. In this paper, the Zn-22wt%Al powder compromising fine spherical particles is first produced by gas atomization, compacted, and then consolidated by solution heat treatment. This is found to produce billets with a very fine-grained microstructure, which were subsequently utilized in extruding helical gears at a temperature of 250°C and a strain rate of 2.36×10s. The specifications of these helical gears are: module, 0.2; number of teeth, 12; helix angle, 20°; pitch diameter, 2.55 mm; and internal diameter, 1.5 mm. An investigation of the mechanical properties of the extruded gears through Vickers hardness test and extrusion load measurement, and SEM observation, confirms the effectiveness of superplastic Zn-22wt%Al eutectoid alloy powders for the production of miniature hollow helical gears. [ABSTRACT FROM AUTHOR]

On the present work the objective is to manufacture a AA2014+10 vol-% Intermetallic (NbAl3 or FeAl2 ) metal matrix composites. Since Powder Metallurgy route was chosen, the powder mixtures of metallic powders which forms AA2014 alloy and intermetallic powders were obtained by mechanical alloying. Powder mixtures were cold die pressing and green samples were hot extruded. As result of this intermetallic addition, mechanical properties of AA2014 alloy are improved and a tensile strength of 516 MPa on AA2014+NbAl3 and 465MPa on AA2014+FeAl2 within an elongation close to 2% on both metal matrix composite materials are reached.El objeto del presente trabajo es la obtención de los materiales compuestos AA2014 +10 vol-% NbAl3 o FeAl2. Para ello se realizó la mezcla inicial de los polvos metálicos que constituyen la aleación AA2014 y de los polvos de estos intermetálicos seguido de su aleación. Las mezclas obtenidas se compactaron en frío y los compactos en verde se extruyeron en caliente. Como resultado de la adición de los intermetálicos se mejoran las propiedades mecánicas de la aleación AA2014, alcanzándose resistencias a tracción de 516 MPa para el AA2014+NbAl3 y de 465MPa para el AA2014+FeAl2, con un alargamiento próximo al 2.0% en ambos materiales compuestos de matriz metálica.

Manufacturing and characterization of bearing materials is the object of the present work. Thus, graphite particles are added to an aluminium matrix as lubricant. It was added as nickel coated graphite in order to avoid a strength decreasing. Mixing of powders following by cold compaction and hot extrusion was the manufacturing way. Extruded materials showed good graphite distribution into the aluminium matrix, with densities between 3.11 to 3.75 g/cm3 as a function of the nickel/graphite content. Hardness and radial crushing strength decrease when graphite content is increased. On the contrary, friction properties are improved with the graphite content because it decreases friction coefficient and wear. Diffusion heat treatment on extruded materials improves furthermore these friction properties but it decreases the radial crushing strength.El objeto de este trabajo es la obtención y caracterización de materiales compuestos (MMC´s) para la fabricación de cojinetes para fricción en seco. Así se incorpora a una matriz de aluminio, partículas de grafito para actuar como lubricante si bien en forma de grafito recubierto de níquel para disminuir la perdida de resistencia que presentan estos materiales. La fabricación de estos materiales se realizó mediante compactación de las mezclas de polvos en matriz y su extrusión en caliente. Los materiales obtenidos presentaron una buena distribución del grafito en la matriz de aluminio, con densidades entre 3.11 g/cm3 y 3.75 g/cm3 según el contenido de níquel/grafito. La dureza y la resistencia al aplastamiento radial disminuyen al aumentar el contenido en grafito. No obstante, un mayor contenido en grafito si mejora las propiedades a fricción del material, disminuyendo el desgaste ocasionado y reduciendo el coeficiente de fricción. El tratamiento térmico de difusión de los materiales extruidos mejora sus propiedades de fricción si bien disminuye su resistencia al aplastamiento radial.

Highlights: [•] An Al–Zn–Mg–Cu alloy is processed by direct hot extrusion of a premixed powder. [•] The effect of heat treatment prior to extrusion is investigated. [•] As-extruded microstructure is highly dependent on the heat treatment prior to extrusion. [•] The alloy extruded from presintered compact shows superior mechanical properties. [ABSTRACT FROM AUTHOR]

We investigated the extrusion behavior of mechanically alloyed Zn-22wt%Al powders with different lubricants and green-compact shapes. The mechanical alloying of powder particles was performed by planetary ball milling for 4 h, 8 h, 16 h, 32 h, and 64 h. The mechanical properties of these powders, as compacted and sintered cylindrical preforms, were estimated by uniaxial compression tests. The alloyed powder with an average particle size of 10 μm obtained after milling for 32 h had the highest compressive strength (288 MPa). Extrusions of miniature spur gears with pitch circles of 1.8 mm using the alloyed powder were carried out at different extrusion temperatures. An extrusion temperature of 310°C resulted in the highest Vickers hardness without surface defects when alloyed powder milled for 32 h was used. To investigate the effect of green-compact shape and lubricant on the dimensional accuracy and cracking regions during the first stage of hot extrusion, extrusion experiments with conical- or cylinder-type green compact shapes and BN spray or a graphite lubricant were performed at an extrusion temperature of 310°C. The results showed that the extrusion of spur gears by using the conical-shaped billet and graphite lubricant resulted in a low extrusion load, good surface roughness, a short cracking region during the first stage, and high dimensional accuracy. [ABSTRACT FROM AUTHOR]

The increasing interest in combustion of solid recovered fuels (SRF), whose physical properties may significantly differ from those of conventional solid fuels, draws attention to the handling of these materials. In this article a simple method for evaluating particulate solids flow properties based on a solid extrusion procedure is assessed. The effects of the main geometrical parameters of the tester and of the testing operating condition are investigated. Results are critically discussed by comparing them with the flow properties evaluated in a Schulze ring shear tester. [ABSTRACT FROM AUTHOR]

Abstract: The processing and mechanical properties of rapidly solidified and consolidated hypereutectic Al-20wt% Si alloys were studied. A bulk form of rapidly solidified Al-20wt% Si alloy was prepared by extruding gas atomized powders having a powder size of 106–145μm. Powder extrudates were subsequently equal channel angular pressed up to eight repetitive route C passes to refine matrix microstructure and Si particles by imposing severe plastic deformation. The microstructures of the gas atomized powders, extrudates and equal channel angular pressed samples were investigated via a scanning electron microscope. The mechanical properties of the bulk samples were measured by compressive tests. Equal channel angular pressing was found to be effective in matrix grain and Si particle refinement, which enhanced the strength of the Al-20wt% Si alloy without deteriorating ductility in a range of experimental strain of up to 30%. [Copyright &y& Elsevier]

We studied the effects of deformation and annealing of n-type 90Bi2Te3-5Sb2Te3-5Sb2Se3 thermoelectric compound. Hot-extrusion was conducted to prepare the deformed compound and then this compound was annealed at 400°C for 1-24 hr. When the undoped cast-ingot was extruded, the compound was changed from p-type to n-type due to the electrons generated during the extrusion process. For the compound extruded with SbI3-doped powders, the thermoelectric properties were also varied for the extrusion process. After annealing at 400°C more than 9 hr, the powder-extruded compound was recrystallized. This caused a decrease in carrier concentration and crystallographic anisotropy. In case of the compound extruded at the ratio of 10:1, the Seebeck coefficient α and the electrical resistivity ρ increased due to recrystallization. However, thermal conductivity κ of the compound decreased. This resulted in an increase in the figure-of-merit from 1.23 x 10-3 to 1.63 x 10-3 K-1. [ABSTRACT FROM AUTHOR]

Al-20Si alloy with high thermal conductivity and adequately low coefficient of thermal expansion is successfully produced by hot extrusion of pre-alloyed powder and used as a model material in investigating the influences of heat treatment on the thermal properties of the material. In the as-extruded samples, fine Si particles are distributed uniformly in the Al matrix. When the alloy is annealed at 250 °C or 400 °C for 2 h, neither the Al nor Si grains grow significantly, but the internal strain developed in extrusion is relieved. Therefore, thermal conductivity is improved to 148.0 W/(m·K) and the coefficient of thermal expansion is reduced to 17.3 × 10−6/K. With further increasing annealing temperature to 560 °C, the coarsening of Al and Si grains occurs. On one hand, it significantly reduces the grain boundaries and phase boundaries in the material, consequently further increasing the thermal conductivity to 174.8 W/(m·K). On the other hand, the coarsened structures lead to thermal stress during cooling, which offsets the constraining effect of Si on the thermal expansion of Al and results in an increase in the coefficient of thermal expansion. • Fabricating Al-20Si alloy with good thermal properties by powder extrusion • Investigating microstructures by combined technology of EBSD and EDS • Studying the effects of annealing on microstructures and thermal properties • Revealing the internal stress generated in sample cooling and its effects on CTE [ABSTRACT FROM AUTHOR]

Pre-alloyed micron-sized 6005A Al alloy (AA 6005A) powders, with a Mg/Si atomic ratio of 0.75, obtained by high pressure inert gas atomization were consolidated by uniaxial cold pressing at 200 MPa into cylindrical Al containers and hot extruded at 450, 480 and 500 °C with an extrusion rate of 7:1, followed by artificial T6 precipitation hardening. Ageing conditions were varied between 170 °C and 190 °C and times of 6, 7 and 8 h. The microstructure of the extruded profiles was analysed using X-Ray diffractometry (XRD), light optical microscopy (LOM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Differential scanning calorimetry (DSC) was used to study the possible phase transformations. After our results, the peak-aging hardness condition was achieved at 180 °C for 6 h. Mechanical properties of the powder metallurgy (P/M) aluminium alloys consolidated by hot extrusion were superior to those of the extruded profiles of wrought alloy using conventional ingot metallurgy (I/M) billets. AA 6005A wrought P/M alloy via T6 heat treatment shown yield stress of 317 MPa and elongation of 21% at the extrusion pre-heating temperature of 500 °C. [ABSTRACT FROM AUTHOR]