Papers by Keyword: Hot Extrusion

Abstract: Ultimate tensile strength (UTS) becomes a primary concern in direct recycling of metal chips. This study investigates the influences of preheating temperature, preheating time and volume fraction of alumina on the tensile strength performance. The parameters of temperature, time and volume fraction of micro alumina were varied between 450 - 550 oC, 1 - 3 hours and 5 - 15% respectively. The full factorial design with center point analysis was employed to analyse the effect of process variables on the response. A total of 19 experimental runs were performed through the hot extrusion operation. The preheating temperature and volume fraction were identified as the key variables affecting the UTS. An optimum UTS was obtained for the profile extruded at 550 oC, 3 hours duration and 5% volume fraction of alumina.

Abstract: Products by solid-state recycling of aluminum chips in hot extrusion process were controlled by temperature related parameters using preheating temperature 450 °C, 500 °C, and 550 °C for 1 hr, 2 hr, and 3 hr preheating time. By using Design of Experiments (DOE), the results found that the preheating temperature is more important to be controlled rather than the preheating time and increasing of temperature led to the high tensile strength. The profile extruded at 550 °C with 3 hr duration had gained the optimum case to get the maximum tensile strength. For the optimum case, heat treatment was carried out using quenching temperature at 530 oC for 2 h and aging process at 175 oC for 4 h. The tensile strength of extrudes specimen was improved significantly compared to those of non-treated specimen.

Abstract: Aluminium-Matrix-Nanoparticle-Composites were produced by ball milling of micro scale Aluminium powder with various nanoscales ceramic powders like Silicon Carbide, Alumina and Boron Nitride with subsequent consolidation by hot extruding. The composites were investigated by amplitude dependent damping tests, tensile tests at elevated temperatures, hardness measurements, imaging methods and electric conductivity tests. All tested samples were machined out of hot extruded rods. The Amplitude dependent damping of bending samples was determined by measuring the strain dependent logarithmic decrement of free decaying vibrations of bending beams at room temperature. These tests were done after successive step by step isochronal heat treatments. Some samples show substantial improvement of the mechanical properties due to dispersion hardening or grain refinement. It can be concluded that the results are mainly influenced by dislocation effects like Orowan-effect, work-hardening, grain-size-hardening, recrystallization, and creation of dislocations at ceramic particles due to thermal mismatch. Moreover some results can be attributed to fatigue during mechanical cycling namely crack nucleation, crack growth and fraction. The electric conductivity was measured indirectly by permeability tests with a digital hysteresis recording devise. The results show the low influence of nano-particle dispersion hardening to conductivity in comparison of work-hardening.

Abstract: Aluminum alloy metal matrix composites are a class of materials object of large and intensive research during the last years. In this study an AA2124 aluminum alloy were processed by means of mechanical alloying added by 10, 20 and 20 percent of silicon carbide (SiC) in vibratory SPEX type mill during 60 and 120 minutes. After this the composites powders obtained were characterized by means of Scanning Electron Microscopy (SEM) plus Energy Dispersive Spectroscopy (EDS) to determine the powders morphology. In order to consolidate the AA2124 aluminum alloy composites reinforced by silicon carbide (SiC) composites, the powders processed by high energy ball milling technique were hot extruded and the billets were characterized by SEM to determine the microstructure and the distribution of the reinforced ceramic phase of silicon carbide throughout the aluminum matrix and at last the microhardiness Vickers technique were used to evaluate the mechanical properties.

Abstract: The effects of solution treatment on the microstructure evolution of hot-extruded Cu-15Ni-8Sn alloy were investigated by optical microscope (OM), scanning electronic microscope (SEM), differential scanning calorimetry (DSC) and tensile testing, and the effects of solution temperature and time on the mechanical properties of the alloys were analyzed. The results indicated that, the γ-phases precipitated at first and then dissolved with the extension of the solution time during solutionizing at 800 C,the volume fraction of theγ-phase reached its peak at about 1h. However when solutionizing at 860°C, theγ-phase solely dissolved gradually with the extension of the solution time . In addition, a small amount of annealing twins appeared intragranular in the process of solution treatment. The γ-phase dissolution and the grain growth of α (Cu) were the main softening factors of the alloy during the solution treatment. Through overall consideration, the optimum solution treatment was annealing at 840°Cfor 1 h.

Abstract: In the present work, aluminum AA6061 chip metals were extruded by hot extrusion and the effect of extrusion parameters on the mechanical properties and surface integrity were investigated. The objective of the present studies it to analyze the mechanical and structural properties of 6061 after plastic consolidation by hot extrusion. Tensile test results showed that material extruded using temperature 550°C exhibit higher ultimate tensile strength (UTS) compared with temperature of 400°C. Fracture surfaces shown that ductile fracture mode occurred at condition 500°C and 2 hours, and brittle fracture occurred at condition 400°C.

Abstract: In this research, mechanical properties of recycled 6061 aluminium alloy, produced by solid state recycling through extrusion, were compared to as-received billets. Aluminum 6061 chips were extruded using a hot extrusion machine. The effects of extrusion parameters on the mechanical properties of the produced recycled 6061 aluminium alloy were investigated. The objective of the study was to analyze the mechanical and structural features of the alloy after plastic consolidation. The extrusion processes were conducted at different preheat temperatures and preheat times, while the ram speed was kept constant. The findings of the study highlighted the potential of combining the extrusion process parameters as an efficient processing route for production of high quality and high-performance type of extruded billets. Tensile test results showed that, material extruded at 550°C exhibited better mechanical properties compared to that extruded at 400°C. The higher temperature resulted in a higher tensile strength being produced, at the expense of a trade-off in ductility. Overall, it was revealed that, the ultimate tensile strength (UTS) and elongation (ETF) of the produced recycled 6061 aluminium through extrusion exhibited mechanical and structural properties comparable to those of the as-received billets.

Abstract: Ferritic ODS 14Cr steels reinforced by means of Yttrium oxide nanoclusters represent one of the options for future structural applications in nuclear Generation IV reactors. Due to their high tensile properties and resistance to irradiation damage, Oxide Dispersion Strengthened Steels (ODS-S) have been suggested for nuclear fusion applications. The present paper describes the experimental procedure of mechanical alloying, canning and hot extrusion adopted to produce ODS rods. The effect of variations in the processing parameters are also discussed. Hot extrusion has been successfully applied to produce a batch of about 10 kg of ODS steel. Full size ASTM E21 and E8 specimens have been tested from room temperature up to 800 °C. The microstructure characterization of the manufactured materials has been carried out by transmission electron microscopy. Ultimate tensile stress higher than 1350 MPa have been obtained in the as-extruded material and higher than 1100 MPa in samples annealed for 4 hours at 800 °C.

Abstract: This paper aims to manufacture magnesium alloy tubes with gradient hardness using hot extrusion process. A two-stage porthole die together with a mandrel is designed to have a straight channel part combined with a conical part. Materials are pushed through this specially-designed die cavity to generate a non-uniform velocity distribution at cross sections between the mandrel and the die and result in different strain and strain rate distributions. Accordingly, a gradient microstructure or hardness product can be obtained. Using the finite element analysis, the effective strain distributions inside the die cavity and at the die exit are firstly discussed for various inclination angles in the conical part of the mandrel. Then, hot extrusion experiments with a two stage porthole die set are conducted to obtain magnesium alloy products with gradient microstructures and hardness. Using a die set of mandrel inclination angle of 10^o and die inclination angle of 25^o, gradient microstructures of grain sizes of 4.30μm, 5.92 μm and 3.67μm at the outer surface, center zone, and inner surface, respectively, are achieved.

Abstract: The paper presents results of structural studies of hot extruded NiTi shape memory alloy that is in the B2 phase at room temperature. Texture of the alloy was determined from the X-ray diffraction measurements. It was found that in result of 60 % sample reduction (at a cross-section of a bar formed by hot extrusion) weak axial texture - type <110>_B2 was formed. The volume of the grains oriented in this way was approx. 20 %. Basing on metallographic observations it was also found that the size of the grains formed as a result of the thermomechanical treatment was uniform with the average area of 1700 μm². This information is significant from the point of view of functional properties. Hot extruded alloy revealed presence of the reversible martensitic transformation. Its characteristic temperatures were slight higher than in as-cast alloy. Moreover, the extruded NiTi alloy showed 100 % of the shape recovery.