Influence of cooling rate and composition on formation of intermetallic phases in solidifying Al–Fe–Si melts

Abstract

Aluminium alloys containing 0·3%Fe and 0·05%Si, 0·3%Fe and 0·15%Si, 0·3%Fe and 0·45%Si, and 0·5%Fe and 0·2%Si were solidified with different cooling rates. Shapes of intermetallic particles and their spatial distribution in the alloys were characterised by optical and scanning electron microscopy. X-ray diffraction analysis was used to establish the types of intermetallic phases extracted from the alloys by dissolving the FCC matrix in boiling phenol. The influence of melt superheating on the microstructure was analysed by comparing phase portraits of alloys solidified from melts whose temperatures before casting were 100 and 350°C above the liquidus.

On a solidifié des alliages d’aluminium contenant 0·3%Fe et 0·05%Si, 0·3%Fe et 0·15%Si, 0·3%Fe et 0·45%Si et 0·5%Fe et 0·2%Si, à différentes vitesses de refroidissement. On a caractérisé la forme des particules intermétalliques et leur distribution spatiale dans les alliages, au moyen de la microscopie optique et de la microscopie électronique à balayage. On a utilisé l’analyse de la diffraction des rayons X pour établir les types de phases intermétalliques extraites des alliages par dissolution de la matrice FCC dans du phénol en ébullition. On a analysé l’influence de la surchauffe du bain sur la microstructure en comparant les images de phase des alliages solidifiés à partir des bains dont les températures avant le moulage étaient de 100 et de 350°C au-dessus du liquidus.     

The isothermic annealing of bainite

Abstract

Bainitic high carbon steel has been isothermally annealed in the temperature range, 823–973K, in order to follow changes in structure and mechanical properties. The kinetic data for carbide coarsening were found to be in substantial agreement with the Ostwald ripening theory at the higher annealing temperatures. The observed divergence from the theory at the lower temperatures is attributed to the influence of grain boundary diffusion.

The dependence of mechanical properties on structure has been examined in relation to several important models. Good data correlation was found in all cases but agreement with predicted values of slope and intercept constants was found only for the models based on the Orowan theory of hardening.

The responses to annealing of upper and lower bainite are substantially different and result in measurable differences in mechanical properties of the two structures after heat treatment.

Résumé

Les auteurs ont fait des recuits isothermes dans la gamme de température de 823 à 973°K sur un acier bainitique à haute teneur de carbone afin de suivre les changements de structure et de propriétés mécaniques. Aux températures plus élévees, les résultats sur la cinétique de grossissement des carbures sont en accord substantiel avec la théorie d'Ostwald. Aux températures plus basses, la divergence des résultats avec la théorie est attribuée à l'inf1uence de la diffusion intergranulaire.

Les auteurs ont examiné l'influence de la structure sur les propriétés mécaniques en fonction de plusieurs modéles importants. La corrélation des résu1tats est en bon accord dans tous les cas, mais seulement les modéles basés sur la théorie de durcissement d'Orowan prédisent des pentes et des ordonnées á l'origine qui sont en accord avec les résultats.

Les réponses au revenu des bainites supérieure et inférieure sont substantiellement différentes, ce qui se traduit par des différences mesurables dans les propriétés mecaniques des deux structures aprés traitement thermique.     

The annealing of explosively deformed copper

OFHC copper explosively deformed at pressures between 75 and 435 kbars is characterized by high residual stresses, compressive near the surface and tensile further in. Annealing after this deformation takes place in three some what overlapping stages. Property changes associated with these stages and possible interpretation of the effects are discussed in detail. Contrary to the annealing behavior of conventionally deformed metals, the first stage of annealing is accompanied by adecrease in density and anincrease in electrical resistivity. It is postulated that these changes are due to stress relief and microcrack growth. Also, unlike most conventionally deformed materials, the major softening stage is found to have recovery rather than recrystallization characteristics. The data in this stage are quantitatively consistent with a mechanism involving dislocation annihilation.     

Synthesis and properties of Cu–Al–Ni shape memory alloy strips prepared via hot densification rolling of powder preforms

Abstract

Cu–Al–Ni shape memory alloy strips were successfully prepared by a powder metallurgy route consisting of preparing powder preforms from premixed Cu, Al and Ni powders by cold compaction, stepwise sintering in the range 873–1273 K, followed by unsheathed multipass hot rolling at 1273 K in protective atmosphere. The densification behaviour of the sintered powder preforms during hot rolling has been discussed. Homogenisation of the hot rolled strips was carried out at 1173 K for 4 h. It has been shown that the finished Cu–Al–Ni alloy strip consisted of self-accommodated plates ofβ' and γ' martensites together with a small amount of nanocrystalline Cu₉Al₄ phase. The finished hot rolled Cu–Al–Ni strips had fracture strength of 476 MPa, coupled with 2·5% elongation. The shape memory tests showed almost 100% recovery after 10 thermomechanical cycles in the hot rolled strips at 1 and 2% applied prestrain.     

The annealing behaviour of deformed particle-containing aluminium single crystals

Deformed particle-containing single crystals of initial orientation (001)[110] whose deformation behaviour is discussed in an accompanying paper [Acta metall. mater. 42 (1994)] have been annealed until partially or fully recrystallised. At particles larger than 3 μm and at strains greater than 0.7, particle stimulated nucleation of recrystallisation (PSN) occurs. The PSN grains have well defined orientations, and at least two PSN orientation components have been identified. These orientations are among those predicted by a deformation model presented in the accompanying paper. At strains of less than 2.3, the PSN grains are often outgrown by other texture components. Under these circumstances the PSN grains are frequently left as “island grains” within the rapidly growing grains, and the contribution of the PSN orientations to the texture of the fully recrystallized material may be small. At strains of 2.3, some of the PSN grains may grow as rapidly as the other grains. The rapidly growing grains often have a platelike habit and an orientation relationship of approximately 40° about a 〈111〉 axis to the deformed matrix. However, in some cases, equiaxed grains with other orientation relationships to the matrix show rapid growth. The relative growth rates of grains of different origin provides very strong evidence of oriented growth during recrystallisation.     

Microstructural investigation of as cast and PREP atomised Ti–6Al–4V alloy

Abstract

A microstructure characterisation of Ti–6Al–4V is conducted for cast, extruded and micrometre sized particles. The plasma rotating electrode process is used to produce spherical Ti–6Al–4V powders from an alloy electrode. The process parameters and their impact on the material properties are described. The effects of electrode rotation speed on the particle size distribution, particle shape and crystal structure are investigated in detail. Optical microscopy and scanning electron microscopy are used for microstructural characterisation. The analysis shows that cast and extruded Ti–6Al–4V alloys have equiaxial α and α+β phase structures, while plasma rotating electrode processed powder from the same alloy compositions has an acicular or martensitic (α) structure. The microstructure scale depends on the particle size. Microhardness measurements are used to assess mechanical property dependence on the microstructure of this alloy. The rapidly cooled alloy particles have much higher hardness than cast or extruded bulk alloy.     

On enhancement of hypoeutectic aluminium–silicon powder metallurgy alloy

Abstract

Currently, there exists a considerable demand within the automotive industry for the development of aluminium–silicon alloys that can be processed through powder metallurgy (PM) technologies. As such, a study aimed at the development of a new hypoeutectic aluminium–silicon PM alloy (Al–6Si–4·5Cu–0·5Mg–0·2Sn) was recently undertaken. Although the preliminary data were encouraging, it was postulated that a refinement of the bulk alloy chemistry could yield additional gains. In the present work, the sintering response mechanical properties of this alloy were enhanced by making controlled adjustments in composition. The influence of the amount and raw powdered sources of copper, magnesium and tin were the principal variables investigated. Using XRD and metallographic examination, it was determined that a decrease in the copper content to 3·0 wt-% improved ductility significantly. Furthermore, the incorporation of magnesium as an elemental powder versus an Al–Mg master alloy improved sintering behaviour significantly, while tin additions up to 0·2 wt-% increased yield stress and hardness. The optimised alloy exhibited a threefold increase in ductility as well as a 25% gain in yield strength.

Présentement, il existe une grande demande dans l’industrie de l’automobile pour le développement d’alliages aluminium silicium qu’on peut obtenir par les techniques de métallurgie des poudres (PM). Ainsi, on a récemment entrepris une étude visant au développement d’un nouvel alliage hypoeutectique aluminium silicium (Al-6Si-4·5Cu-0·5Mg-0·2Sn) par PM. Bien que les données préliminaires soient encourageantes, on a postulé qu’un raffinement de la chimie de l’alliage brut pourrait produire des gains additionnels. Dans le présent travail, on a amélioré les propriétés mécaniques de la réponse au frittage de cet alliage en faisant des ajustements contrôlés de la composition. L’influence de la quantité et l’influence des sources de poudres brutes de cuivre, de magnésium et d’étain étaient les principales variables examinées. En utilisant la XRD et l’examen métallographique, on a déterminé qu’une diminution de la teneur en cuivre à une valeur de 3·0% en poids améliorait significativement la ductilité. De plus, l’incorporation du magnésium comme poudre élémentaire par rapport à un alliage maître d’Al-Mg améliorait significativement le comportement de frittage, alors que des additions d’étain jusqu’à 0·2% en poids augmentaient la limite élastique et la dureté. L’alliage optimisé exhibait une augmentation triple de la ductilité ainsi qu’un gain de 25% de la limite d’élasticité.     

Zr_(55)Al_(10)Ni_5Cu_(30)非晶态合金的制备与性能研究

采用石墨坩埚浇铸法在真空中频感应熔炼炉中制备Zr55Al10Ni5Cu30合金,并对合金进行了金相、X射线衍射和显微硬度的测试,考察原料纯度、过热度及冷却速率对非晶态合金性能的影响。结果表明,采用工业级原料就可以制备出性能良好的非晶态合金,在低的冷却速率下形成的非晶态合金具有相对较高的硬度,适当提高过热度可以减少微晶的形成。     

Influence of minor Zr and Ti on microstructures and properties of Al–8·6Zn–2·5Mg–2·2Cu alloys

Abstract

The effect of minor Zr and Ti elements on microstructures and properties of Al–8·6Zn–2·5Mg–2·2Cu alloys was investigated. The results show that there is no significant change in the grain size by simultaneous addition of Zr and Ti as compared to individual additions of Zr or Ti to Al–8·6Zn–2·5Mg–2·2Cu alloy. The ability of restraining recrystallisation of Al–8·6Zn–2·5Mg–2·2Cu–0·16Zr–0·04Ti alloy is weaker than that of alloy Al–8·6Zn–2·5Mg–2·2Cu–0·16Zr alloy, since Ti and Zr have a poisoning interaction. The corresponding tensile properties, hardness and stress corrosion cracking resistance of the Al–8·6Zn–2·5Mg–2·2Cu–0·16Zr alloy were decreased by addition of Ti.     

The Application of Ni – Ti Shape Memory Alloys as Fasteners

This article covers the various materials aspects of the shape memory alloys that go into the design of fastening devices. A brief overview of the shape memory phenomenon and the martensite transformation during free and constrained recovery has been given to clarify the role of the martensitic transformation in the success of this application. Finally, the design of an Ni–Ti–Fe fastening sleeve has been discussed.     

中国古代铜器的显微组织

总结了28年来作者对中国考古发掘出土逾千件铜器显微组织的研究成果,表明:中国古代铜及铜合金有纯铜、砷铜、锡青铜、铅青铜、铅锡青铜、黄铜、铅黄铜、银铜、砷白铜及镍白铜等;它们的显微组织显示了铸造、冷热加工组织以及室温长期埋藏条件下铜合金组织发生的变化,以及不同时代、不同地区显示的特征等;与现代铜及铜合金金相图谱有诸多不同.这些研究成果丰富了铜及铜合金金相学的内容.     

In situ neutron diffraction analysis of stress-free d-spacing during solution heat treatment of modified 319 Al alloy engine blocks

Abstract

Aluminium alloy engine blocks have successfully replaced ferrous materials in order to maximise weight savings and improve vehicle fuel efficiency. However, the development of an optimal heat treatment process is required to improve engine block casting integrity and prevent potential problems such as in-service cylinder distortion. Optimisation of heat treatment parameters requires an in-depth study to determine how residual stresses are relieved with time during solution heat treatment. In order to perform this analysis, however, in situ neutron diffraction must first be carried out on stress-free samples of the same composition and processing history as the engine blocks to account for factors such as thermal expansion and changes in lattice parameter due to dissolution of secondary phases. The results from this study suggest that thermal expansion caused the largest change in d₀ spacing, while prolonged exposure at the solutionising temperature resulted in relatively small changes in {311} and {331} d₀ spacing due to phase dissolution.     

低温贝氏体转变对中碳钢韧性的影响

摘要：沉淀硬化钢中纳米富Cu相的析出,使微应变（α）发生改变,这不仅影响力学性能,也对腐蚀性能产生作用。为了探索α对腐蚀性能和力学性能的影响规律,通过XRD谱型分析,对商用钢LJ338ESR 在300～600℃不同时间时效析出富铜纳米相后的α、硬度和电荷转移电阻（Rf）进行了研究。结果表明,300～450℃时效,8h前α值随时效时间延长而升高,8h后由于析出相与基体失去共格,α随着时效时间延长而降低;硬度与α变化相似。600℃时效,α在时效2h达到峰值,这归因于共格微应变和逆变奥氏体两种相反因素的共同影响;600℃逆变奥氏体生成,使硬度变化较小。析出相与基体保持共格时,Rf和α随时效时间的变化呈良好的反比关系,即Rf随α的增大而减小。     

Combined effect of bismuth content and cooling rate on microstructure and mechanical properties of Al–8·5Si–0·4Mg–0·3Fe alloy

Abstract

This study investigates the combined effect of Bi content (0·1, 0·2, 0·4 and 0·5 wt-%) and cooling rate (from 0·7 to 4°C s^?1) on the microstructure, tensile characteristics, quality index and two-parameter Weibull modulus of an Al–8·5Si–0·4Mg–0·3Fe alloy. Results show that Bi refined the eutectic Si structure and that increasing the cooling rate intensified the refining efficiency. The thickness of the β-Al₅FeSi intermetallic decreased with an increase in the cooling rate, but no significant effect was observed with the addition of Bi. The contour maps of mechanical properties suggest that the effect of cooling rate on mechanical properties was more significant than that of Bi additions. The highest Weibull modulus for the base alloy and Bi containing alloy was obtained at the cooling rate of 4°C s^?1. Decrease in the thickness of β intermetallic phase and reduced porosity with increasing cooling rate appeared to cause a decreased variability of UTS data.

Cette étude examine l’effet combiné de la teneur en Bi (0·1, 0·2, 0·4 et 0·5% en poids) et de la vitesse de refroidissement (de 0·7 à 4°C s^?1) sur la microstructure, les caractéristiques de tension, l’index de qualité et deux modules de Weibull d’un alliage d’Al–8·5Si–0·4Mg–0·3Fe. Les résultats montrent que le Bi raffine la structure de l’eutectique de Si et que l’augmentation de la vitesse de refroidissement intensifie le rendement du raffinement. L’épaisseur de l’intermétallique Al₅FeSi-β diminuait avec une augmentation de la vitesse de refroidissement, mais on n’a pas observé d’effet important avec l’addition de Bi. Les tracés du contour des propriétés mécaniques suggèrent que l’effet de la vitesse de refroidissement sur les propriétés mécaniques était plus important que celui des additions de Bi. On a obtenu le module de Weibull le plus élevé pour l’alliage de base et pour l’alliage contenant du Bi à la vitesse de refroidissement de 4°C s^?1. La diminution de l’épaisseur de la phase intermétallique β et une réduction de la porosité avec une augmentation de la vitesse de refroidissement semblaient résulter en une diminution de la variabilité des données d’UTS.     

不同增强相弥散强化铜的导电性

用高能球磨冷压烧结方法制备了Cu/Al2O3和Cu/WC弥散强化铜，检测和分析了其导电性能。结果表明：两种弥散强化铜的电阻率实验值均大于其计算值。同一增强相含量越高，弥散强化铜导电性越低。相同体积分数不同，增强相的Cu/Al2O3和Cu/WC的导电性能相近。     

Cathodic reduction process of Al–Cu–Y alloy in fluoride-oxide eutectic system via molten salt electrolysis

Al-Cu-Y alloys were prepared by molten salt electrolysis in fluoride-oxide system composed of electrolyte(Na_3 AlF_6-AlF_3-LiF-MgF_2) and oxide(Al_2 O_3-CuO-Y_2 O_3). Cathodic reduction process of Al_2 O_3,CuO and Y_2 O_3 were analyzed by cyclic voltammetry and chronoamperometry. Components and phase composition of alloy samples prepared by potentiostatic electrolysis were characterized by scanning electron microscopy and energy dispersive spectroscopy. The results show that the Al-Cu-Y alloy can be prepared in the AIF_3-NaF-5 wt%LiF-5 wt%MgF2(NaF/AlF_3 = 2.2, molecular ratio) eutectic system with mixed oxide(Al_2 O_3-CuO-Y_2 O_3) through 2 h at the conditions of a temperature of 1208 K, cell voltage3.0 V, cathode current density 0.7 A/cm~2. Al(Ⅲ) and Cu(Ⅱ) ions can be reduced to zero valence Al(0) and Cu(0) directly on carbonaceous electrode surface by instantaneous nucleation, respectively, the reduction process is controlled by diffusion. The reduction potential of Y(Ⅲ) ions is close to the active ions of fluoride melts, but strengthened phase AI3 Y can be formed through electrochemical reduction and alloyed process with active Al(Ⅲ) and Cu(Ⅱ) ions, meanwhile, the Al_2 Cu and Al_3 Y phases are distributed at the grain boundary of Al matrix.     

Al—Mg—Sc—Zr合金的再结晶行为的研究

研究了Al-Mg-Sc-Zr合金的再结晶行为,结果表明：Al-Mg-Sc-Zr合金的再结晶起始温度为400℃,经小弥散的析出相对位错,晶界的钉轧作用是合金再结晶温度大幅度提高的主要原因。     

The effect of heat treatment on corrosion behaviour of Ni–P–3 gr/lit Cu nano-composite coating

In this investigation, the effect of heat treatment on corrosion behaviour of Ni–P–Cu nano-composite coating was studied. Initially, an Ni–P–(3?g?l^?1) Cu nano-composite coating was produced under the bath condition of pH?=?4.5–5, RPM?=?400. The coatings were then heat treated at 400°C for 1?h. Scanning electron microscope (SEM), electron dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques were employed to analyse the coating characteristics. As well, corrosion resistance of the coatings in a solution of 1?M HCl was explored by potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). Results show that heat treatment for 1?h at 400°C crystallised the Ni–P–Cu coating and changed the amorphous morphology of the coating. This crystallisation also decreased corrosion resistance mainly due to P content reduction of the nano-composite coating. Finally, heat treatment reduced the P content of the coating as it formed different phases such as Cu₃P, Ni₈P₃, Ni₅P₂ and CuP₂.