Al Al3Ni Research Articles

Enhanced Mechanical Strength and Electrical Conductivity of Al–Ni‐Based Conductor Cast Alloys Containing Mg and Si

The electrical conductivity (EC), mechanical strength, hot tearing susceptibility (HTS), and related microstructure of Al–xNi–0.55Mg–0.55Si conductor alloys (x = 1–4 wt%) are investigated. Adding Mg and Si into Al–Ni‐based alloys, numerous β″/β′ precipitate after T5 and T6 treatments, thus significantly improving the EC and mechanical strength. The HTS of the alloys reduces significantly as the Ni content increases, mainly because of an increase in the eutectic Al–Al3Ni and a reduction in the grain size. Under T5 condition, the tensile strengths increase gradually with the Ni content and reach a medium strength level, with yield strength (YS) of 158–205 MPa and EC of 47.1–50.7% IACS. After applying T6, all alloys achieve a high strength, with YS of 246–287 MPa and EC of 47.7–51.1% IACS. However, the strength decreases with increasing Ni content. In general, the Al3Ni–0.55Mg–0.55Si alloy presents a better trade‐off among HTS, YS, and EC among the four alloys investigated. Due to its excellent properties (EC of 49.4% IACS and YS of 178 MPa in T5, and EC of 49.7% IACS and YS of 250 MPa in T6), the Al3Ni–0.55Mg–0.55Si alloy is a promising material for the fabrication of Al conductor cast alloys.

Al-Al3Ni In Situ Composite Formation by Wire-Feed Electron-Beam Additive Manufacturing.

The regularities of microstructure formation in samples of multiphase composites obtained by additive electron beam manufacturing on the basis of aluminum alloy ER4043 and nickel superalloy Udimet-500 have been studied. The results of the structure study show that a multicomponent structure is formed in the samples with the presence of Cr23C6 carbides, solid solutions based on aluminum -Al or silicon -Si, eutectics along the boundaries of dendrites, intermetallic phases Al3Ni, AlNi3, Al75Co22Ni3, and Al5Co, as well as carbides of complex composition AlCCr, Al8SiC7, of a different morphology. The formation of a number of intermetallic phases present in local areas of the samples was also distinguished. A large amount of solid phases leads to the formation of a material with high hardness and low ductility. The fracture of composite specimens under tension and compression is brittle, without revealing the stage of plastic flow. Tensile strength values are significantly reduced from the initial 142-164 MPa to 55-123 MPa. In compression, the tensile strength values increase to 490-570 MPa and 905-1200 MPa with the introduction of 5% and 10% nickel superalloy, respectively. An increase in the hardness and compressive strength of the surface layers results in an increase in the wear resistance of the specimens and a decrease in the coefficient of friction.

Tensile, wear, and corrosion behaviors of an in situ Al–Al3Ni metal matrix composite solidified under different cooling rates

Tensile, wear, and corrosion behaviors of an in situ Al–Al3Ni metal matrix composite solidified under different cooling rates

Novel synthesis and magnetic properties of Ni@NiO nanoporous nanowires

We present a novel route to fabricate Ni@NiO nanoporous nanowires (NPNWs) through simple chemical dealloying of rapidly solidified Al–Al3Ni fibrous eutectic precursor in an alkaline solution. The dealloying inheritance effect and spontaneous oxidation of nanostructured Ni play vital roles in the formation of Ni@NiO core-shell (NiO shell on the Ni core) NPNWs. The length scale (nanowire diameter) of the Ni@NiO NPNWs could be regulated by facilely changing the rotating speed (cooling rate) during fabrication of the Al–Ni precursor. The Ni@NiO NPNWs exhibit unique magnetic properties, including lower saturation magnetization and enhanced coercivity relative to bulk Ni, commercial Ni powders (∼75 μm) and Ni nanoparticles (∼50 nm). Such exceptional magnetic properties could be rationalized in terms of the surface effect (the NiO shell), the core-shell structure and the shape anisotropy of nanowires. Moreover, this strategy can be generalized to fabricate other nanoporous nanowire materials as the introduction of traditional metallurgical solidification technique into the synthesis of advanced nanomaterials.

Critical Assessment 40: A search for the eutectic system of high-temperature cast aluminium alloys

A quest for the eutectic system of novel cast aluminium alloys, having high-temperature capabilities, is critically assessed with two potential candidates of Al–Al3Ni and Al–Al11Ce3 examined and compared to the presently used Al–Si base. The conventionally cast Al–Al3Ni and Al–Al11Ce3 eutectics do not exhibit the anticipated advantage over Al–Si in strengthening retention at temperatures up to 500°C. The promising differences between diffusivities of silicon, nickel, and especially cerium in aluminium, and eutectic melting temperatures, accompanied by high coarsening resistance of Al3Ni, Al11Ce3 phases and the eutectic hardness retention are inconsistent with observed similarities in the temperature-related strengthening-reduction of all three eutectics. These findings will help defining the criteria for development of the eutectic system, suitable for future heat-resistant aluminium alloys.

In situ Composites: A Review

The review of the works on the fabrication-technology studies, patterns of structure formation, and properties of in situ composites is presented. The main advantage of in situ (natural) composites is the thermodynamic stability of their composition and the coherence (conjugation) of the lattices of the contacting phases. All these ones provide the composite with a high level of the physical and mechanical properties. As shown, composite materials of this type are formed in the process of directed phase transformations, such as eutectic crystallization, eutectoid decomposition, etc., caused by a temperature gradient, as well as a result of diffusional changes in composition. The conditions for the growth of in situ composites are formulated. The mechanisms of growth of composite structures of the eutectic type are considered. The factors influencing on the morphology of structures of the eutectic type are indicated. The considered technological methods make it possible to obtain materials with predetermined properties, in which the size, volumetric composition, and spatial arrangement of phases are characteristic of in situ composites. The paper provides a large number of examples of in situ composites: from low-melting Bi-based alloys to refractory eutectics based on Mo and W (Bi–MnBi, Cd–Zn, Al–Al3Ni, Al–Al4La, Al–Al10CaFe2, Al–Al9FeNi, Al–Al3Zr, Al–Al3Sc, Au–Co, Si–TaSi2, Cr–HfC, Cr–ZrC, Cr–NbC, Cr–NbC, Cr–TaC, Nb–Nb5Si3, Mo–ZrC, Mo–HfC, W–TiC, W–ZrC, W–HfC, etc.). Processes and aspects of structure formation are considered. The influence of additional doping on the structure and properties of composite materials of the eutectic type of binary systems, as well as the features of the structure formation of ternary colonies in the composite are considered.

Effect of cooling rate on microstructure and microhardness of hypereutectic Al–Ni alloy

High solidification cooling rates during unsteady-state conditions of solidification of Al-based alloys can induce different microstructural length scales or metastable phases, leading to improved properties. The present study aims to characterize the microstructural arrangement of the hypereutectic Al–8 wt%Ni alloy, unidirectionally solidified in unsteady-state heat flow conditions, examining the influence of the cooling rate in the development of the Al–Al3Ni eutectic and the primary phase. A columnar-to-equiaxed macrostructural transition is shown to occur at a solidification cooling rate (Ṫ) of about 4.8 °C/s, with different microstructures associated with each morphological zone. The observation of microstructures of hypoeutectic, eutectic and hypereutectic Al–Ni alloys, has permitted an asymmetric coupled zone diagram to be proposed. The microstructural interphase spacings of the Al–8 wt%Ni alloy are experimentally determined and correlated to Ṫ, and the Vickers microhardness (HV) is shown to decrease with the increase in such spacings. The higher experimental HV profile of the examined hypereutectic alloy as compared to that of the eutectic Al–Ni alloy is attributed to the formation of a supersaturated solid solution of Ni in α-Al.

Development and characterization of Al–Al3Ni–Sn metal matrix composite

The Al–Al3Ni–Sn composite was developed using a powder compassion and sintering metallurgical processing route. Microstructures of the sintered samples revealed the combination of a globular, chain-like and elliptic (raindrop) Al3Ni phases. The differential scanning calorimetry (DSC) analysis confirmed the high temperature stability of the composite. After heat treatment conducted at 500 °C, the Al3Ni chain-like phase in the matrix transformed to raindrop particles. The presence of the Al3Ni intermetallic compound had a positive effect on the hardness since the Al–Al3Ni–Sn composite was harder in comparison to the A356 aluminium alloy. Microstructures were analysed using the LEO 1525 field-emission scanning electron microscope (FE-SEM). The XPS scanned spectra of the A356-Ni-Sn alloy revealed the Al2p, Si2p, C1s, Sn3d5, O1s, Ni2p3 and Mg1s intensity peaks.

Outstanding strengthening behavior and dynamic mechanical properties of in-situ Al–Al3Ni composites by Cu addition

The microstructure, mechanical properties, and dynamic mechanical properties of the various intermetallic-reinforced in-situ Al–Al3Ni eutectic composites were investigated for different compositions with increasing Cu content. The microstructure changes from a nanofiber-like Al3Ni-reinforced composite structure to a various intermetallic-reinforced composite structure. Moreover, the addition of Cu induces changes in the phases composing the composite, especially the kind of intermetallic compounds, such as Al3Ni, Al3NiCu, Al7Ni4Cu, and Al2Cu. According to these microstructural evolutions, the mechanical strength under compressive loading is drastically enhanced from about 200 to 1200 MPa, and a typical strength-ductility tradeoff, e.g., the plasticity is reduced from more than 70% to less than 2% with the strength increase, is also observed. The precipitation behavior which can lead to improving further strengthening was observed employing in-situ TEM, Vickers hardness, and DSC investigations. The damping properties are also improved with increasing Cu content, especially at high-temperatures; but regrettably, the maximum operating temperature is decreased. We will discuss the origin of the enhanced strength and propose a route to obtain composites with optimized mechanical and damping properties for application in different fields.

Studying on the morphology of primary phase by 3D-CT technology and controlling eutectic growth by tailoring the primary phase

Morphology and alignment of the structure determine material properties. In the present work, the morphologies of the typical primary Al2Cu and Al3Ni phases in hypereutectic alloys are studied by 3D-CT technology, and their growth characteristics have been clarified further. The experimental result reveals that the Al2Cu and Al3Ni phases grow with a faceted characteristic at a lower growth rate, and the transition from the faceted phase to the non-faceted phase occurs with the increase of growth rate. It is also found that the application of the temperature gradient or/and the magnetic field is capable of controlling the growth of the primary Al2Cu and Al3Ni phases, and the alignments of the primary Al2Cu and Al3Ni phases remarkably affect that of the Al–Al2Cu and Al–Al3Ni eutectic. This implies that the eutectic phase can be controlled by tailoring the primary phases during imposing the magnetic field or/and temperature gradient. Finally, a simple model of controlling the growth of the eutectic phase by tailoring the primary phase is proposed. The present work can deepen the understanding on the growth characteristics of the Al2Cu and Al3Ni phases and offer a new method to control the eutectic phase by tailoring the primary phase.

Effect of heat treatment on tensile and fatigue deformation behavior of extruded Al-12 wt%Si alloy

This study investigated the effect of heat treatment on tensile and high-cycle fatigue deformation behavior of extruded Al-12 wt%Si alloy. The material used in this study was extruded at a ratio of 17.7: 1 through extrusion process. To identify the effects of heat treatment, T6 heat treatment (515 °C/1 h, water quenching, and then 175 °C/10 h) was performed. Microstructural observation identified Si phases aligned in the extrusion direction in both extruded alloy (F) and heat treated alloy (T6). The average grain size of F alloy was 8.15 °C, and that of T6 alloy was 8.22 °C. Both alloys were composed of Al matrix, Si, Al2Cu, Al3Ni and AlFeSi phases. As T6 heat treatment was applied, Al2Cu phases became more finely and evenly distributed. Tensile results confirmed that yield strength increased from 119.0 MPa to 329.0 MPa, ultimate tensile strength increased from 226.8 MPa to 391.4 MPa, and the elongation decreased from 16.1% to 5.0% as T6 heat treatment was applied. High-cycle fatigue results represented F alloy’s fatigue limit as 185 MPa and T6 alloy’s fatigue limit as 275 MPa, indicating that high-cycle fatigue properties increased significantly as heat treatment was conducted. Through tensile and fatigue fracture surface analysis, this study considered the deformation behaviors of extruded and heat treated Al-Si alloys in relation to their microstructures.

Al based ultra-fine eutectic with high room temperature plasticity and elevated temperature strength

Developments of aluminum alloys that can retain strength at and above 250°C present a significant challenge. In this paper we report an ultrafine scale Al–Fe–Ni eutectic alloy with less than 3.5at% transition metals that exhibits room temperature ultimate tensile strength of ~400 MPa with a tensile ductility of 6–8%. The yield stress under compression at 300°C was found to be 150 MPa. We attribute it to the refinement of the microstructure that is achieved by suction casting in copper mold. The characterization using scanning and transmission electron microscopy (SEM and TEM) reveals an unique composite structure that contains the Al–Al3Ni rod eutectic with spacing of ~90nm enveloped by a lamellar eutectic of Al–Al9FeNi (~140nm). Observation of subsurface deformation under Vickers indentation using bonded interface technique reveals the presence of extensive shear banding during deformation that is responsible for the origin of ductility. The dislocation configuration in Al–Al3Ni eutectic colony indicates accommodation of plasticity in α-Al with dislocation accumulation at the α-Al/Al3Ni interface boundaries. In contrast the dislocation activities in the intermetallic lamellae are limited and contain set of planner dislocations across the plates. We present a detailed analysis of the fracture surface to rationalize the origin of the high strength and ductility in this class of potentially promising cast alloy.

In situ formation of Al–Al3Ni composites on commercially pure aluminium by friction stir processing

Possibility of the formation of Al–Al3Ni composite layers on commercial pure aluminium plates by friction stir processing (FSP) has been studied. It is believed that the hot working nature of FSP can effectively promote the exothermic reaction between Al and added Ni powder to produce Al3Ni intermetallic compounds in the aluminium matrix. In this study, the effects of the rotational and traverse speed of the tool as well as the number of FSP passes on the in situ formation of Al3Ni in aluminum matrix were examined. Besides, the microstructure and microhardness of the fabricated surface layers were also studied. The results showed that the ratio of tool rotational speed to traverse speed (ω/υ) is the main controlling parameter of the heat generated during FSP and hence the reaction between aluminium and nickel. Increasing the number of FSP passes also promoted the reaction between Ni and Al and improved the distribution of Al3Ni compounds, too. The composite layer achieved by six passes of FSP showed the highest hardness, which was almost twice of that of the base metal.

Nanocrystalline matrix Al3Ni2–Al–Al3Ni composites produced by reactive hot-pressing of milled powders

Mechanically alloyed nanocrystalline Al63Ni37 powder with a metastable structure of NiAl intermetallic phase was mixed with 30 vol.% of Al powder. This powder mixture was consolidated under the pressure of 7.7 GPa at 600, 700, 800 and 1000 °C for 15 and 180 s. During the consolidation, in all cases, the metastable NiAl phase transformed into the equilibrium Al3Ni2 intermetallic. Moreover, a solid-state reaction between the intermetallic matrix and Al occurred, yielding an Al3Ni phase. Progress of this reaction depended on the consolidation temperature and temperature exposure time, thus Al3Ni2–Al, Al3Ni2–Al–Al3Ni or Al3Ni2–Al3Ni composites were produced by hot-pressing with various parameters. The mean crystallite size of the Al3Ni2 intermetallic matrix in the composites is 39–67 nm, depending on consolidation parameters. The composites hardness is in the range of 6.02–7.51 GPa.

Mechanism of Gravity Effect on Solidification Microstructure of Eutectic Alloy

The influence of gravity on the solidification microstructure of Al–Al3Ni eutectic alloy was investigated by using a 50-m-long drop tube. It was found that at different growth rates the average inter-rod spacing was always larger under microgravity (μg) than those under normal gravity (1g). Moreover, with increasing growth rate, the spacing difference between 1g samples and μg samples reduced progressively. Based on the experimental results and analysis, a physical model was proposed to describe the effect of gravity on the solidification process of eutectic alloy.

Nanocrystallization and Mechanical Properties of Rapidly Solidified Amorphous Al<sub>86</sub>Ni<sub>6</sub>Y<sub>6</sub>Ce<sub>2</sub> (at.%) Alloy

Primary crystallization of amorphous Al86Ni6Y6Ce2(at.%) alloy was investigated through differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and X-ray diffraction. Moreover, nanoindentation analysis was performed to relate the hardness to the structure of the alloy. The kinetic parameters of the first crystallization process were determined by Kissinger method. The average amount of Avrami exponent (n=1.7±0.21) was concluded the primary crystallization occurred through three dimensional diffusion-controlled growth with decreasing rate. The α-Al nanoparticles 58 nm in size homogeneously embedded in the glassy matrix were formed during primary crystallization. Significant changes in the hardness occurred due to the change of the crystalline structures. The hardness of 7.30±0.58 GPa was obtained by annealing at 618 K with a microstructure of Al nanoparticles and Al3Ni intermetallic compound in an amorphous matrix.

The characterization investigation of laser-arc-adhesive hybrid welding of Mg to Al joint using Ni interlayer

Laser-arc-adhesive hybrid welding technology is used to merge Mg to Al joints with a Ni interlayer. In this study, the effect of the adhesive on microstructure and intermetallics are analyzed. The adhesive and Ni interlayer restrain the reaction between Mg and Al. The transition zone between Mg and Al is composed of the Mg–Mg2Ni eutectic and Al–Al3Ni peritectic. The function of the Ni interlayer on the fusion zone is strengthened with the addition of the adhesive. The tensile shear test load of the laser-arc-adhesive hybrid welding of Mg to Al joints is 2.15kN and 118MPa without curing the adhesive. The harmful effects of the intermetallics are significantly reduced and the property of the joint is improved.

A mean-field micromechanical study on thermal-cycling creep of short fiber-reinforced metal matrix composites: Al–Al3Ni eutectic composites

In this study, a unified mean-field micromechanical model was applied to analysis of thermal-cycling creep of short fiber-reinforced metal matrix composites subject to a wide range of external loads from compression to tension. The model considered the rate process of the local mass transfer by diffusion along the fiber/matrix interface. The thermal-cycling creep of the composites can be divided into three groups observed in high compressive stress regime, low compressive and tensile stress regime, and high tensile stress regime based on the micromechanical examination of the deformation mechanism. Numerical and experimental studies were systematically conducted with directionally solidified Al–Al3Ni eutectic composites. These studies demonstrated that even though compressive loads were applied, the elongate creep deformation occurred under given thermal-cycling conditions, and thermal-cycling creep was largely affected by the length of the fiber and temperature profile.

An alloy solidification experiment conducted on Shenzhou spacecraft

To gain a better understanding of how gravity-driven phenomena affect the solidification and crystal growth of metallic materials, directional solidification experiments have been performed on an Al–Al3Ni eutectic alloy and an Al–Bi monotectic alloy on board the unmanned Chinese Shenzhou III spacecraft during its flight. For sake of comparison, identical experiments were also performed in the laboratory on earth. The results of investigations applying metallographic, SEM, EPMA and image analysis techniques are reported. Some interesting differences between the samples solidified in space and their counterparts solidified on the ground are described.

Formation of Al3Ni Nanofibers in an Al-Based Metal Matrix Composite Fabricated by Reaction Sintering

We developed an Al2O3 and Al3Ni intermetallic reinforced Al-based metal matrix composite by sintering an Al-20 wt% NiO powder compact at 1000 °C. Differential thermal analysis showed that a two-step reaction took place between Al and NiO in the temperature range 600–650 °C. The initial stage was a solid-state reaction, but it was soon paused by the newly formed Al2O3 and Al3Ni phases that separated the Al and NiO grains. A liquid–solid reaction was later resumed as the temperature was increased above the eutectic temperature of Al–Al3Ni at 640 °C when molten Al–Ni appeared. When the molten sample was quenched to room temperature, a two-phase Al–Al3Ni eutectic was found in the sample. In comparison with the air-quenched and the oil-quenched samples, the sizes of proeutectic Al3Ni grains and Al–Al3Ni eutectic phases in the salt-solution-quenched sample were much finer. The eutectic contained Al3Ni nanofibers with a diameter of approximately 50 nm. A reaction model of Al and NiO was proposed. A thermodynamic model was also proposed to describe the formation of the composite.