Tensile and fatigue properties of cold and warm compacted Alumix 431 alloy

Abstract

In this experimental study, tensile and fatigue properties of the Alumix 431 alloy (Al, Zn, Mg and Cu alloys) produced using the conventional press and sinter processes in different pressures and temperatures are investigated. The results clearly showed that the warm compacted specimens can reach the mechanical properties of the cold compacted ones under less pressure. In the fatigue tests it was observed that fracture started from large pores as shown in all scanning electron microscope (SEM) examinations and ductile fracture occurred. 85% of the 180 MPa/80°C and 77% of the 230 MPa/RT specimens fractured at the machined surface. Tensile and fatigue properties of warm compacted (180 MPa/80°C) and cold (230 MPa/RT) compacted specimens are almost equal at these same densities. This result indicates the economic benefit of warm compaction by the much lower applied compaction pressure.     

Investigation of warm compaction and sintering behaviour of aluminium alloys

Abstract

The effects of warm compaction on the green density and sintering behaviour of aluminium alloys were investigated. Particular attention is paid to prealloyed powders, i.e. eutectic and hypereutectic Al-Si alloys, regarding their potential applications in the automotive industry. The effects of chemical composition, alloying method, compacting temperature and the amount of powder lubricant were studied. The compaction behaviour was examined by an instrumented die enabling simultaneous measurement of density, die wall friction coefficient, the triaxial stresses acting on the powder during the course of compaction and ejection pressure. The sintering behaviour was studied via dilatometeric analysis as well as normal batch sintering. The results show that warm compaction could be a promising way to increase the green density of aluminium alloys, especially prealloyed powders, and to decreased imensional instability during sintering. Moreover, it reduces the sliding friction coefficient and the ejection force during the powder shaping process. This paper presents the significant advantages and drawbacks of using the warm compaction process for commercial PM aluminium alloys.     

Study of warm compaction of Alumix 123 L

Abstract

Although powder metallurgy (PM) material is dominated by ferrous alloys, there is a growing interest in Al PM. The usage of Al PM in automotive applications depends on the development of higher density and improved dynamic properties. Several approaches have been proposed to increase density of sintered parts. Warm compaction process of Al powder was used to achieve high density. In this study the authors focused on the effect of warm compaction on Alumix 123 L (ECKA Granules) powder blend. It has been found that warm compaction at 110°C led to a reduction in the ejection force by 27·9%, increased green density to 94% of theoretical density and increased sintered strength to 315 MPa as compared to those pressed at room temperature.     

Relationship between physical structure and machinability of green compacts

Abstract

The dependence of green machinability on compact density and strength was investigated for room temperature and warm compacted steel powder compacts containing two different types of lubricant. Brazilian disc compression tests were employed to determine green strength, while machinability was assessed in terms of response to drilling.

For the room temperature compacted materials, it was found that high compact densities and strength were not, in most cases, associated with improvements in machinability. Furthermore, it was shown that lubrication (both type and quantity) and compaction pressure plays a critical role in determining the level of breakouts observed. In contrast, the use of warm compaction, in conjunction with specially designed lubricants, has been shown to be a suitable method of producing high density, high strength compacts while retaining good green machining characteristics. Mechanisms responsible for the observed behaviours of both the room temperature and warm compacted specimens have been forwarded in the present paper.     

温粉高速压制装置及其成形试验研究

为发展粉末冶金零件高致密化成形技术,提出1种高速压制和温粉压相结合的温粉高速压制(WHVC)成形技术.自行设计并制造了1套利用重力势能驱动的温粉高速压制成形装置,并对温粉高速压制成形实验进行探讨.结果显示:运用该装置对316L不锈钢粉、铁粉、铜粉和铝粉进行温粉高速压制成形实验,生坯密度分别可达到7.47、7.63、8....     

Consolidation and green body characteristics of gelcast metallic powder

Abstract

A preliminary study concerning the compaction of metallic powder was carried out in order to investigate a rarely explored route in powder metallurgy, to form complex geometry parts, known as gelcasting. Green bodies produced with as supplied stainless steel powder showed a tendency to form foam, which affected the surface finishing. The mechanical behaviour of green compacts was also affected by the processing additives present in the metallic powder. Organics in the as supplied powder were removed by thermal treatment at 500°C and additional samples were produced. Although no difference in green density was observed, these samples displayed better surface finish and mechanical characteristics, as a result of improved adhesion between the polymer network and particle surface. The results showed that the gelcasting process is able to produce green parts suitable for subsequent thermal treatment.     

Behaviour of metal powders during cold and warm compaction

Abstract

An instrumented die was used to investigate the behaviour of metal powders during cold (ambienttemperature) and warm (up to 140^°C) compaction. This instrument enables simultaneousmeasurement of density, die wall friction coefficient, the triaxial stresses acting on the powderduring the course of compaction and ejection pressure. Commercial iron, titanium, aluminium,316L stainless steel (SS) and aluminium–silicon powders were employed for investigation. Theresults demonstrated the advantages of powder preheating on the compaction behaviour of metalpowders concerning green density, dimensional changes, frictional behaviour, ejectioncharacteristics and compactibility. However, the outlines also determined that the response ofthe non-ferrous powders to powder preheating is somehow different from those of the ferrouspowders. In this context, the behaviour of prealloy aluminium–silicon powders during compactionwas found of particular interest, as their compactibility is strongly affected by powder preheating,whereas the dimensional changes after ejection decrease considerably. This article presents theeffect of cold and warm compaction on the consolidation and ejection characteristics of ferrousand non-ferrous metal powders. The influence of compaction condition (pressure andtemperature) with considering of the powder characteristics and densification mechanisms areunderlined.     

ELEVATED-TEMPERATURE COMPACTION OF METALS AND CERAMICS BY GAS PRESSURES

Abstract

Techniques have been developed for the isostatic compaction of metals, cermets, and ceramics with no appreciable variation in density throughout the compacted structure. The temperatures needed are much lower than those normally utilized for sintering, so that a fine-grain, tough structural material can be produced. The starting material may be loose powder, cold-pressed preforms, explosively impacted preforms, coated particles, spherical particles, or vibratory-packed powder.

Toxic materials are easily handed. Since the process is quite adaptable to the preparation of complex shapes by direct compaction of powders, components can be produced from the more expensive materials, such as beryllium and tungsten, with a minimum loss of material during processing.     

‘Double strength for green parts’ claim ushers in new Hoeganaes technology…

Hoeganaes Corporation has introduced a high green strength powder that it says gives up to twice the green strength for conventionally produced ferrous metal powder parts. The aim of ANCORMIX HGS is to produce metal powder premix materials that help prevent crack formation during part ejection, and other problems associated with green parts without warm compaction or high compression techniques.This is a short news story only. Visit www.metal-powder.net for the latest powder metallurgy industry news.     

THE ROLLING OF COPPER STRIP FROM HYDROGEN-REDUCED AND OTHER POWDERS

Abstract

Copper powders were rolled to form strip in a normal two-high mill. Satisfactory green strip was obtained from the low-density powder produced by hydrogen reduction from aqueous solution, provided that a mechanical method was used to feed the powder into the rolls. All the types of powder investigated required considerable further rolling after compaction, with at least two heat-treatments, to produce normal mechanical properties.     

Powder Metallurgy Group Meeting,Stratford-Upon-Avon, 3–4 November 1975: Report of Proceedings

Abstract

The key steps of a PM technique for manufacturing fully dense near net shape tool steel parts are described. The main production steps are powder preparation, compaction, and sintering. The pre- alloyed powders used in the process are annealed to soften them, making compacting to fairly high green densities possible. Sintering to full density is accomplished at a closely controlled temperature near the solidus of the material. The heat treatment response of sintered high-speed steel parts is similar to that of conventionally produced steels. A model for the calculation of the necessary carbon content to achieve full hardness during the heat treatment of high-speed steels was developed. The model is based on predicting the amount and approximate chemical composition of the carbides present after quenching from the austenitizing temperature and the subsequent calculation of the carbon tied up within the carbides. PM/0207     

Effects of Aging and Steam Oxidation on Sintered Irons and Steels Containing Phosphorus

Abstract

Dramatic reduction of ejection forces in a metal powder compaction process has been achieved using a balanced die method. The approach uses a toolset consisting of a thin walled die in a fairly rigid metal, with a rubber sleeve capable of transmitting high radial pressure. By maintaining a pressure balance between internal compaction pressure and external ‘bolstering’ pressure across the thin wall die, the ejection forces were reduced to almost zero. With limited equipment available, the compaction process was carried out in incremental stages to produce cylindrical metal billets of 32 mm diameter by 20 mm height. Green densities of 6·49 Mg m^?3 were achieved for NC100 iron powder supplied by Höganäs at much lower compaction pressure than those reported elsewhere. PM/0711     

Model for uniaxial compaction of ceramic powders

Abstract

A phenomenological yield criterion has been proposed for modelling the uniaxial compaction processes of various ceramic powder compacts on the basis of continuum mechanics. It includes three parameters to characterise the geometric hardening of the powder compact and the strength of the base material. The model was applied to uniaxial compaction of three ceramic powders which possess different particle size distribution, particle morphology, and base material property. The values of parameters in the yield criterion were determined through the uniaxial compaction experiment. Using the yield criterion, the elastoplastic finite element calculation was carried out to analyse the compaction of the three ceramic powders.     

MECHANICAL PROPERTIES OF SINTER/FORGED LOW-ALLOY STEELS

Abstract

The paper describes preliminary work on sinter/forged low-alloy steels. The mechanical properties and structures of both atomized and blended alloys were investigated. By using a good-quality atomized powder of the SAE 4600 type, tensile and fatigue properties equivalent to those of wrought steels could be obtained. Atomized alloy powders with higher oxygen contents had poor ductility and impact values because of surface oxides on the powder particles.

Blended iron alloys gave tensile strengths up to 72 tonf/in² (1112 MN/m²) with much higher ductility and impact-resistance than would be obtained with conventionally pressed and sintered alloys.     

Analysis of compaction behaviour of wet granulated aluminium alloy powder

Abstract

The compaction behaviours of wet granulated aluminium powder were examined by uniaxial die compaction, and their effect on rearrangement and plastic deformation was analysed by using the Cooper–Eaton equation. Based on the calculation results and structure/morphology of the granulated powder, a new compaction model for granulated powder, which consists of three compaction mechanisms (macrorearrangement, microrearrangement, and plastic deformation), and a modified equation has been proposed in this study. A macrorearrangement indicates it to be a dominant factor on the compaction behaviour of granulated powder and the modified equation is sufficient to analyse the compaction behaviour.     

THE EFFECT OF PHOSPHORUS ADDITIONS ON THE TENSILE,FATIGUE, AND IMPACT STRENGTH OF SINTERED STEELS BASED ON SPONGE IRON POWDER AND HIGH-PURITY ATOMIZED IRON POWDER

Abstract

The mechanisms operating during the sintering of iron-phosphorus PM alloys are discussed, as well as the factors contributing to the unique combination of strength, ductility, and toughness that is characteristic of these materials. Alloying methods are reviewed with special reference to powder compressibility, tool wear during compaction, and homogenization during sintering. The preferred production method is to add phosphorus in the form of a fine Fe₃P powder to iron powder. The mechanical properties of a number of sintered steels made with and without Fe₃P additions to sponge iron or to high-purity atomized iron powders are reported. Use of atomized powder makes it possible to reach extremely high density by single pressing and the resulting phosphorus-containing sintered steels have very high ductility and impact strength. The fatigue strength is related linearly to the tensile strength, with a correlation coefficient of 0·91. It is concluded that structural factors other than those that control ductility and toughness are responsible for the fatigue resistance of sintered steels.     

用温压制造汽车变速器输出轴毂

汽车中应用的铁基粉末冶金零件在不断增加,这主要是由于密度的增高和动态性能的改进。粉末冶金零件的新应用还必须通过不断采用新工艺的最终形成形能力及减少制造工序,降低生产成本。用于制造某些新零件的生产工艺,还必须能生产出几何形状复杂的薄壁零件。采用温压工艺(ANCORDENSETM),用一次压制可达到较高密度水平。这种工艺还能增高生坯强度与减小脱模力。汽车变速器输出轴毂在20世纪90年代以前,是用二次压制/二次烧结工艺大量生产的一个重要粉末冶金零件。1995年前后,用温压工艺进行了制造这种零件的试验,并和用二次压制/二次烧结工艺生产的零件进行了对比。     

温压技术的应用、发展及其在我国的工业化前景

根据国内外粉末冶金零件市场的走势，论证了温压技术在我国工业化的重要性。综述并讨论了温压技术的应用及发展趋势。介绍了作者们开发的温压专用粉末加热装置和温压成形粉末冶金材料的性能，其成果为温压原材料及设备的国产化打下了基础。     

Metal powder compacting dies: optimised design by analytical or numerical methods

Abstract

The initial data needed to design metal powder compaction die are: compact shape and density, powder mix composition, compaction and radial pressure, part number and tool materials. The design targets are: diameters of insert and ring, sometimes number of rings and interference or interferences. The constraints include: no tensile stresses on the insert, no risk of relative motion at part ejection, no unwanted alteration of material microstructures and maximum stresses always below the allowable limits. Usually the design is based on engineering experience, company knowhow, and approximated analytical calculations and cost considerations.

This study is focused on the use of numerical methods to determine the design parameters of dies for powder compaction. Both room temperature and warm compaction have been investigated. Numerical algorithms, implemented into FEM calculation codes, enable one to optimise the common diameter of insert and ring, corresponding to the lowest stresses on both items, or to find the minimum value of the outer diameter. A wide range of compaction pressures, die materials and geometries, interferences and allowable stresses have been explored. To compare the results, based either on analytical or numerical methods, circular dies have been investigated. The differences among the results depend on the consideration of the actual stressed length, or compact height, and total die length. The calculations by analytical methods overestimate the stresses. The paper presents some suitable nomograms for the comparison of results of calculations performed either by Laméformulas or by sophisticated numerical methods.