Papers by Keyword: Hot Extrusion

Abstract: The hot backward extrusion process of the Mg-Gd-Y-Zn-Zr magnesium alloy was investigated by both numerical simulation and experiments. An axisymmetric 2D rigid-plastic finite element model (FEM) was established to simulate the material flow during the extrusion process. The shapes of the dies were optimized in order to avoid severe stress concentration and obtain uniform deformation of the workpiece. After hot extrusion, the microstructures of the alloys were obviously refined, and the secondary phases which included many long-period stacking order (LPSO) phases precipitated in the matrix. The optimal comprehensive mechanical properties of the alloy have been obtained after extrusion and ageing at 200°C for 48h with the ultimate tensile strength of 434MPa, tensile yield strength of 375MPa and elongation of 4.5%, respectively. The good mechanical properties were mainly attributed to the fine microstructures and numerous precipitates in the matrix.

Abstract: The hot extrusion process may lead to frequently observed textures in the profiles, like fiber structures in longitudinal direction. Aluminum profiles (AA6060) were extruded with different tool types (flat-face dies and modified porthole dies). Compression tests of cylindrical specimens, which were machined out of these profiles likewise in extrusion direction, were conducted to examine possible effects of the in-plane anisotropy in lateral direction. A hardness distribution over the cross section of the specimens was measured. It was found that dependent on tool design and profile geometry, the specimens developed preferred lateral flow directions during upsetting. Simulations of the upsetting test, with assigned Hill parameters to consider anisotropy of the material, showed, that this anisotropy, not the local hardness nonuniformity, is the main reason for the detected plastic flow properties.

Abstract: The processes of manufacturing continuously and discontinuously steel-reinforced aluminum profiles by means of co-extrusion and subsequent forging were examined. In the co-extrusion and subsequent forging of discontinuously reinforced parts, influences of the reinforcing elements on forming behavior and material bonding for both processes were investigated. It was shown that forming temperature as well as ram speed have no influence on joining quality and forming behavior of the reinforcing elements in the co-extrusion of continuously reinforced profiles. The analyses of the joining zone between the composite partners revealed that a good connection of the two materials could be achieved.

Abstract: Silicon nitride possess excellent hot hardness and wear resistance coupled with very good corrosion resistance. Hence, in recent years, silicon nitride has been a serious contender as a reinforcement to develop light weight metal matrix composites for several technological applications. Al6061 is most popular matrix alloy as it possess excellent formability and in particular the quality of extrudates of Al6061 is quite high and are the most preferred in space and naval applications especially for support structures and torpedoes blades respectively. Improved corrosion and slurry erosion resistance on use of silicon nitride in nickel and aluminum alloy matrices have been reported by several researchers. In the light of the above, this paper focuses on development of Al6061-6wt% Si₃N₄ by stir casting the most economical and popular route followed by hot extrusion. Hot extrusion was carried out using 200T hydraulic press at extrusion ratio of 1:10 at a temperature of 550°C. Slurry erosion tests were carried out using 3.5% NaCl solution containing silica sand particles of size 312μm at different rotational speeds varying between 300 rpm and 1200 rpm. The sand concentration was varied from 10g/l to 40 g/l. Under identical test conditions, hot extruded Al6061-6wt% Si₃N₄ composite do possess better slurry erosion resistance when compared with matrix alloy. The mechanism involved in the material removal process during slurry erosion process will also be discussed.

Abstract: The carbon steel/stainless steel composite pipe was prepared by centrifugal compound casting-hot extrusion-cold rolling. SEM was employed in detecting the microstructure and alloy element distribution maps in stainless steel of composite pipe. The mechanical properties were measured through tensile test. The corrosion resistance of the composite pipe was detected in acid, alkali and salt solutions. The results show that the outer and inner layers are integrated with good metallurgical behavior, and the mechanical properties of the composite pipe are satisfactory, the chemical compositions are well-distributed. The grain-boundary corrosion test is qualified. This composite pipe has better corrosion resistance in 10%H₂SO₄ and 10%NaOH solution than in FeCl₃ solution at room temperature.

Abstract: In this work, a comparison study has been performed on the two hot finished manufacturing processes i.e. hot extrusion and hot piercing which are used for manufacturing stainless steel hot finished pipes/tubes. Study is based on different parameters which include raw material, temperature, extrusion ratios, manufacturing process, compressive stresses, shear stresses, friction forces, tooling, etc. The aim of the study is to determine the qualitative difference in the output product which is manufactured through these two processes for hot finished pipes manufactured in austenitic, duplex, super-duplex stainless steels and nickel alloys. The study includes the testing of the hot finished product with non-destructive testing techniques of water immersion ultrasonic testing, Inside Diameter eddy current testing and dye penetrant testing and destructive testing techniques of mechanical testing, microstructure analysis and corrosion testing methods for confirming the qualitative difference in the outputs of both the processes. The products manufactured by hot extrusion are much more superior in terms of defects observed on the inside of the hot finished pipe apart from material soundness, metallurgy and corrosion properties.

Abstract: The microstructure evolution and control for Alloy 690 during cold rolling and annealing treatment was investigated. Cold rolling specimens were deformed in the strain range from 15% to 70% with strain rates from 0.01 to 10s^-1. Subsequent annealing treatment was carried out in the range of 1060~1100°C for dwell time 3~15mins. Rolling reduction, annealing temperature and annealing time except strain rate had obviously influence on grain size and hardness. Little coarsening of grains were observed below 1060°C during annealing treatment, whereas grains coarsened obviously over 1080°C. Besides, the behavior of grain growth for alloy 690 was investigated systematically.

Abstract: The microstructure evolution and mechanical properties of as-extruded Mg-2.5 Zn-0.5Y Mg alloy were investigated. The grainy intermetallic phases (I-phase and w-phase) observed in the as-cast Mg-2.5Zn-0.5Y alloy distributed homogeneously in the hot extruded alloys. Compared with the cast one, the extruded alloy shows predominant mechanical properties as the result of refined microstructure and the dispersed intermetallic phases formed during hot extrusion. The ultimate tensile strength and the yield tensile strength of the extruded alloy were 354.8 MPa and 305.9MPa respectively.

Abstract: Two Ni-based (Ni-Mn-Ga and Ni-Mn-Co-In) ferromagnetic nonstoichiometric shape memory alloys were studied in order to determine the influence of hot extrusion process on macro, microstructure and texture of the studied alloys. The microstructure of the alloys in the as cast state and after extrusion was analyzed by electron backscatter diffraction technique. Typical microstructure of the as cast alloys consisted of radially oriented columnar grains elongated perpendicularly to the casting axis. For the alloys Ni-Mn-Ga and Ni-Mn-Co-In alloys the 10M and 14M modulated martensite were observed, respectively. After extrusion Ni-Mn-Ga samples revealed high density of fibre texture parallel to the extrusion axis. In spite of applying different extrusion parameters it was not possible to avoid cracks and overcome the brittleness of the Ni-Mn-Co-In alloys.

Abstract: The behavior of texture formation in AA5182 aluminum alloy is investigated by hot extrusion tests under equivalent strain rates and temperatures ranging from 5.0×10^-4 s^-1 to5.0×10^-2s^-1 and from 723K to 823K, respectively. After the deformation, {001} (extrusion plane) and {111} double fiber texture is formed in all the deformation conditions. {001} texture develops after the deformation at 823K under equivalent strain rate of 5.0×10^-3s^-1 up to an extrusion ratio of 2.8. The size of {001} grains is larger than the mean grain size, suggesting that the {001} texture formation is attributed to grain boundary migration. Weakening of {001} texture is confirmed in the annealed section of the specimen.