Microstructure and Mechanical Properties of Al-4.9Ni-4.9Ti Alloy Prepared by Mechanical Alloying

Mechanically alloyed Al-4.9Ni-4.9Ti powders were prepared by milling mixed aluminium, titanium and nickel powders, and then consolidated by hot hydrostatic extrusion. The microstructures of milled powders and extruded bars were characterized by X-ray diffraction and transmission eIectron microscopy observation. The results show that mechanical alloying and consolidating processes have great effects on the microstructures and mechanical properties of extruded materials. Polycrystalline materials having an ultrafine grain size may be prepared by mechanical alloying. The strength and thermal stability are improved with the increasing of processing time of mechanical alloying, since grain size decreases and volume fraction of dispersoids increases as milling time increased     

Billet quenching extrusion process as efficient and reliable replacement for conventional extrusion of Al–Cu alloys

Abstract

In order to eliminate the separate solution soaking treatment used for Al–Cu extrudates, the influence of billet heat treatments before the extrusion process on a precipitation hardenable AlCu6PbBi (AA2011) alloy was studied. The hot deformation behaviour of the alloy was studied using compression tests. A comparison of the conventional extrusion process, press quenching and billet quenching (BQ) before extrusion was made in production on a 35 MN press. The transformation kinetics was studied by heat treating homogenised samples in salt baths. The mechanical testing, using tensile tests and the Brinell hardness test, and a microstructural investigation, using light and TEM microscopy, revealed that extrusion using the billet quenching process results in the formation of extrudates with similar mechanical properties, hardness and microstructures as those produced using conventional technology. In the extrudates produced by BQ a supersaturated solid solution is formed directly after cooling in a standing water wave, which makes BQ an efficient and reliable substitute for the conventional extrusion process.     

粉末冶金难变形材料热静液挤压技术进展

综述了热静液挤压技术在烧结态粉末冶金难变形材料挤压成形与粉末体高致密化固结方面的研究进展。简述了热静液挤压工艺原理、工艺特点与适用范围,分析了热静液挤压润滑层形成的影响因素,介绍了热静液挤压润滑介质研制和热静液挤压技术在粉末冶金高比重钨合金、γ-TiAl基合金材料的挤压成形以及纳米晶铝合金、弥散强化铜合金、NdFeB永磁合金等金属粉末体材料的高致密化固结成形方面的应用,指出了热静液挤压工艺的技术优势与发展前景。     

Effect of Al-6063 Billet Quality on the Service Life of Hot Extrusion Die: Metallurgical and Statistical Investigation

The current paper presents results about the effect of Al-6063 billet quality on the service life of AISI-H13 hot extrusion dies based on microstructural and statistical investigation. In the first half of the paper, secondary (remelt) billet cast in-house at local extrusion plant is compared with two sources of primary (smelter) billet by applying different material characterization techniques including optical microscopy, hardness measurement, x-ray diffraction (XRD) analysis, and energy-dispersive spectroscopy (EDS). The second half of the paper evaluates the performance of primary and secondary billet types based on statistical analysis of data collected on 53 hollow-profile dies from a local commercial extrusion setup. It was observed that the secondary billet has a comparatively coarse grain structure, nonhomogeneous distribution of secondary phases, and high hardness that can be associated with poor casting and homogenization practice. Statistical analysis covers overall analysis of collected data followed by detailed study of percentagewise use of billet quality in terms of die profile complexity/extrusion ratio. Analysis has shown that dies extruding a high percentage of secondary billets are more susceptible to early die failure on overall basis. For more complex dies with high extrusion ratio, average die life further reduces with increased percentage of secondary billet usage. Regression models are also proposed for prediction of die life in terms of secondary billet usage and extrusion ratio. Considering results of present microstructural and statistical analysis, some suggestions during in-house billet preparation of secondary billets have been formulated to prevent early die failure.     

Extrusion processing of Al–Li–Mg–Zr alloy

Abstract

The hot deformation behaviour of an Al–Li–Mg–Zr alloy was characterised in hot torsion and extrusion. The alloy was found to have similar hot ductility to existing high strength aluminium alloys, but this could be maintained at higher temperatures. Billets were extruded over a range of process conditions and a limit diagram was constructed for surface cracking. All the extrusions were found to be partially recrystallised after deformation, but the volume fraction of recrystallisation was a strong function of billet temperature and extrusion ratio. In addition, the unrecrystallised areas contained a recovered substructure where the subgrain size was inversely proportional to the temperature compensated strain rate. The as extruded structure was retained during solution treatment and as a result final mechanical properties were strongly dependent on the extrusion conditions. The use of high billet temperatures and low extrusion ratios gave the best combination of strength and toughness.

MST/839     

Application of equal channel angular extrusion to semi-solid processing of magnesium alloy

A new method called new strain induced and melt activated (new SIMA) is introduced firstly through using equal channel angular extrusion (ECAE) as strain induced step in SIMA and completing melt activated step by semi-solid isothermal treatment, by which semi-solid billet with fine spheroidal grains with average grain size of 5 μm can be prepared. Comparing with common SIMA, semi-solid processed satellite angle frame components using semi-solid billet prepared by new SIMA have higher room temperature and 393 K high temperature mechanical properties.     

Influence of undissolved second-phase particles on dynamic recrystallization behavior of Mg-7Sn-1Al-1Zn alloy during low-and high-temperature extrusions

This study investigates the effects of fine and coarse undissolved particles in a billet of the Mg-7Sn-1Al-1Zn (TAZ711) alloy on the dynamic recrystallization (DRX) behavior during hot extrusion at low and high temperatures and the resultant microstructure and mechanical properties of the alloy.To this end,partially homogenized (PH) and fully homogenized (FH) billets are extruded at temperatures of 250 and 450 ℃.The PH billet contains fine and coarse undissolved Mg2Sn particles in the interdendritic region and along the grain boundaries,respectively.The fine particles (＜1 μm in size) retard DRX during extrusion at 250 ℃ via the Zener pinning effect,and this retardation causes a decrease in the area fraction of dynamically recrystallized (DRXed) grains of the extruded alloy.In addition,the inhomogeneous distribution of fine particles in the PH billet leads to the formation of a bimodal DRXed grain structure with excessively grown grains in particle-scarce regions.In contrast,in the FH billet,numerous nanosized Mg2Sn precipitates are formed throughout the material during extrusion at 250 ℃,which,in turn,leads to the formation of small,uniform DRXed grains by the grain-boundary pinning effect of the precipitates.When the PH billet is extruded at the high temperature of 450 ℃,the retardation effect of the fine particles on DRX is weakened by their dissolution in the α-Mg matrix and the increased extent of thermally activated grain-boundary migration.In contrast,the coarse Mg2Sn particles in the billet promote DRX during extrusion through the particle-stimulated nucleation phenomenon,which results in an increase in the area fraction of DRXed grains.At both low and high extrusion temperatures,the extruded material fabricated using the PH billet,which contains both fine and coarse undissolved particles,has a lower tensile strength than that fabricated using the FH billet,which is virtually devoid of second-phase particles.This lower strength of the former is attributed mainly to the larger grains and/or absence of nanosized M2Sn precipitates in it.     

Fertigungsmöglichkeiten von Faserverbundwerkstoffen des Types Metall-Graphit durch Strangpressen

Extrusion Manufacturing Possibilities of Fibre Composite Materials like the Combination Metal/Graphite These paper discusses the possibilities of manufacturing composite materials by common extrusion of envelope tubes and wrapped wires. Experimental results are given and analysed from the material combination graphite/metal. If a great lot of thin wrapped wires are concentrated in an envelope tube (“multi-core” coextrusion), perfect indirect coextrusion only will be possible, if the compound billet is compacted before extrusion. If few thick wrapped wires are concentrated in an envelope tube (“polycore” coextrusion), perfect indirect coextrusion is possible without compacting the compound billet before extrusion. Through indirect reiterate extrusion, using always the same tools and the same small extrusion ratio, it is possible to get a good product only by extrusion. Hydrostatic “multi-core” coextrusion is possible without compacting the compound billet, but the billet preparation needs more work. The envelope tube must have a solid top with the same angle like the die. It is effective to use dies with small angles. The manufacturing of wrapped wires only by extrusion is possible and effective. All variations of extrusion are available for employment. There is no difference in structure between products manufacturing by “multi-core” coextrusion or by drawing. From the geometrical configuration of the wrapped wires in the envelope tube results a different structure by use of indirect reiterate coextrusion.     

形变强化对93W-4.9Ni-2.1Fe合金组织及性能的影响

为研究形变强化工艺对93W-4.9Ni-2.1Fe性能的影响,采用大变形量旋转锻造工艺制备了93W-4.9Ni-2.1Fe合金,并利用SEM与TEM技术分析了旋转锻造态93W-4.9Ni-2.1Fe合金显微组织的形态与尺寸.结果表明:钨合金材料经形变强化后,钨晶粒内部出现由高密度位错形成的胞状组织以及长条状形变晶粒,且粘结相内位错密度较高;旋锻态93W-4.9Ni-2.1Fe合金在具有高强度的同时,保持着一定的延性;旋锻态钨合金的力学性能与变形量及粘结相的分布有关.     

Extrusion upsetting multiple processing in sandglass die

Abstract

A new method of producing ultrafine grain sizes, known as extrusion upsetting multiple processing in sandglass die or sandglass extrusion, has been investigated using a Zn–5Al (wt-%) alloy. Since the shape of the test billet can remain unchanged after sandglass extrusion, the billet can be extruded repeatedly in order to obtain a large plastic strain. Ultrafine grain size can be achieved in the billet material due to the large plastic strain and dynamic recrystallisation during sandglass extrusion. The process technology, and the microstructures, superplasticity, and microhardness of the test material after sandglass extrusion have been studied. The experimental results show that equiaxial ultrafine microstructures can be introduced into the bulk test material during sandglass extrusion and high strain rate superplasticity can be realised.     

Synthesis and characterisation of nanostructured Al–Al3V and Al–(Al3V–Al2O3) composites by powder metallurgy

In this study, the formation and characterisation of Aluminium (Al)-based composites by mechanical alloying and hot extrusion were investigated. Initially, the vanadium trialuminide (Al₃V) particles with nanosized structure were successfully produced by mechanical alloying and heat treatment. Al₃V–Al₂O₃ reinforcement was synthesised by mechanochemical reduction during milling of V₂O₅ and Al powder mixture. In order to produce composite powders, reinforcement powders were added to pure Al powders and milled for 5?h. The composite powders were consolidated in an extrusion process. The results showed that nanostructured Al-10?wt-% Al₃V and Al-10?wt-% (Al₃V–Al₂O₃) composites have tensile strengths of 209 and 226?MPa, respectively, at room temperature. In addition, mechanical properties did not drop drastically at temperatures of up to 300°C.     

Predicting the variation of the exit temperature with the initial billet temperature during extrusion to produce an AZ31 profile

The extrusion process to produce a cross-shaped profile of a wrought magnesium alloy AZ31 was simulated to predict the exit temperature as a function of the initial billet temperature. Three-dimensional FE simulation revealed the evolutions of temperature and extrusion pressure during the process. The initial billet temperature was found to have a stronger influence on the breakthrough pressure than ram speed. It also played an important role in determining the exit temperature and the temperature rise during the process, especially when ram speed was high. At a given ram speed, the relationship between the temperature rise and the initial billet temperature was found to be linear. Such a relationship could be used as guidelines to optimize the extrusion process and to maximize its throughput.     

Powder Hot Pressing and Front Pad Extrusion Method for Aluminum-Lithium Based Metal Matrix Composites

A simple powder metallurgy (P/M) route was adopted to fabricate aluminium-lithium based metal matrix composites (MMCs) reinforced by submicron SiC particulate by directly hot pressing mixed powders and extrusion. The consolidation behavior of the as-mixed MMC powder and matrix powder during the hot pressing were investigated. In order to avoid fir-tree cracking on the extrudate's surface, a soft metal pad (A16061) was put between the die and the billet. By this method, the MMCs were successfully extruded without any surface cracking, and all the extrudates were found to be covered by a thin layer of the pad material. This is illustrated by the flow pattern of the extrudate and pad material in the dead zone during extrusion. This method, termed as Front Pad Extrusion Method by the authors, is presented here and found to be effective in solving the extrusion problem of P/M aluminum-lithium based MMCs.     

Mikrostrukturelle Pressschweißnahtcharakterisierung im strangpressten Zustand für Al‐Mg‐Si‐Legierungen

Weld seams form when profiles are extruded using porthole or bridge dies. These are inevitable when producing industrial relevant hollow profiles but imply the weak spot if the profiles are used for applications with high mechanical requirements. The characterization of formed weld seams together with their mechanical properties is problematic or sometimes even impossible due to the complex profile geometries. Expansion, bending or tensile tests of profiles or parts of the same were hitherto often used for their analysis lacking the possibility of basic assumptions about their properties. The investigations described herein circumvent the problem by using a flat profile exhibiting the weld seam in the middle. Flat profiles offer the possibility of standardised specimens for tensile testing. The extrusion experiments focused on the aluminium alloys EN‐AW 6060 and EN‐AW 6082. During the experiments billet temperature and extrusion speed have been varied. The microstructure was analysed subsequent to explain the obtained results and to offer a possibility of characterisation.     

Microstructures and Mechanical Properties of Rapidly Solidified Mg-Al-Zn-MM Alloys

Mg-Al-Zn-M M （misch metal） alloy powders were manufactured by inert gas atomization and the characteristics of alloy powders were investigated.In spite of the low fluidity and easy oxidation of the magnesium melt,the spherical powder was made successfully with the improved three piece nozzle systems of gas atomization unit. It was found that most of the solidified powders with particles size of less than 50μm in diameter were single crystal and the solidification structure of rapidly solidified powders showed a typical dendritic morphology because of supercooling prior to nucleation.The spacing of secondary denrite arms was deceasing as the size of powders was decreasing.The rapidly solidified powders were consolidated by vacuum hot extrusion and the effects of misch metal addition to AZ91 on mechanical properties of extruded bars were also examined.During extrusion of the rapidly solidified powders,their dendritic structure was broken into fragments and remained as grains of about 3μm in size.The Mg-Al-Ce intermetallic compounds formed in the interdendritic regions of powders were finely broken,too.The tensile strength and ductility obtained in as-extruded Mg-9 wt pct Al-1 wt pct Zn-3 wt pct MM alloy wereσ-（T.S.） =383 MPa andε=10.6%,respectively.All of these improvements on mechanical properties were resulted from the refined microstructure and second-phase dispersions.     

Fracture life prediction and sensitivity analysis for hollow extrusion dies

It has been reported in literature that extrusion dies most often fail by fatigue fracture. Experimental studies have shown that cracks pre‐exist in dies because of various factors including machining, heat treatment and surface hardening. High levels of repeated mechanical and thermal loads result in crack propagation leading to ultimate fracture failure. In an earlier work by the authors, a simplified approach of plate‐with‐edge‐crack was used to develop a fracture mechanics based fatigue life prediction model for tube dies. In the current work, extrusion die is modeled as a pressurized‐cylinder‐with‐internal‐crack, a more realistic approach for a hollow (tube) die. Stochastic nature of various fatigue‐related die parameters has been used to reflect their variability. Monte Carlo simulation has been performed to forecast fracture failure of extrusion dies under a given set of operating conditions and mechanical properties. Predicted mean‐time‐to‐failure is quite close to actual average extrusion die life data from the industry. Using tube die as a basis, fracture life of other hollow profiles can be estimated through their shape complexity values. Analysis has also been carried out to evaluate how sensitive fracture life of hollow extrusion dies is to material and process parameters. Major findings are that die life is highly sensitive to initial crack size, wall thickness, profile outer diameter and billet length; moderately sensitive to Paris constant and extrusion ratio; and only slightly sensitive to fracture toughness and ram speed. These results can contribute to a deeper understanding of the factors responsible for fracture failure of an extrusion die exposed to thermo‐mechanical fatigue environment.     

Effect of Fe content on the mechanical alloying and mechanical properties of Al-Fe alloys

Al-Fe alloys with Fe contents ranging from 5 to 12 wt% are produced by a double mechanical alloying process (DMA) which consists of a first step of mechanical alloying (MA1) applied to elemental Al and Fe powders, with subsequent heat treatment of MA1 powders to promote the formation of Al-Fe intermetallic phases, and a second mechanical alloying step (MA2) to refine the intermetallic phase, and consolidation of the produced powders by combination of degassing and hot extrusion. The effect of Fe content on the process, as well as on the mechanical properties of the extruded alloys, has been extensively studied. The alloys produced by this process show excellent tensile strength and stiffness at room and elevated temperatures due to the strengthening of Al by intermetallics, as well as to the stabilization of the structure by inert dispersoids.     

Processing and Microstructural Evolution of Superalloy Inconel 718 during Hot Tube Extrusion

The processing parameters of tube extrusion for superalloy Inconel 718 (IN 718), such as slug temperature, tools temperature, choice of lubricant, extrusion ratio and extrusion speed, were determined by experiment in this paper. An appropriate temperature range recommended for the slug is 1080～1120℃, and the temperature range recommended for the tools is 350～500℃. The microstructural evolution of superalloy IN 718 during tube extrusion was analyzed.With the increase of the deformation the cross crystal grains were slightly refined. While the vertical crystal grain is elongated evidently and the tensile strength increased along the axial rake. Glass lubricants have to be spread on the slug surface after being heated to 150～200℃, vegetable oil or animal oil can be used as the lubricant on the surface of the tools to reduce the extrusion force remarkably.     

IN690合金管热挤压温升与挤压力的研究

温升和挤压力是影响钢管挤压过程的重要指标,利用热模拟实验获得了IN690合金的热加工本构关系,建立了IN690合金钢管热挤压过程的有限元模型.采用正交实验设计的仿真实验系统分析了坯料温度（T b=1000～1200℃）、挤压速度（v=20～200 mm/s）和模具预热温度（T d=300～500℃）对管材成形过程中温升...     

Effect of preheat modification on extrusion characteristics of aluminium alloy 2014

Abstract

An extrusion billet is usually homogenized, cooled, and preheated for extrusion by either gas or induction heating. The metallurgical structure of the billet may be modified by a solution treatment during the preheat cycle. In this paper experiments to determine the effect of a solution treatment step during the preheat cycle are described. Torsion tests were performed to establish the optimum preheat cycle and to determine the effect of the modified sequence on the constitutive relationships of the material. Subsequent extrusion tests confirmed that significant increases in ram speed could be obtained and the permissible working area of extrusion limit diagrams could be enlarged by the modified preheat.

MST/122