Al Si Powder Research Articles

Microstructure and Properties of a Laser-Surface-Modified Mg-RE Alloys with Al-Si Powder

Microstructure and Properties of a Laser-Surface-Modified Mg-RE Alloys with Al-Si Powder

Fabrication of hypereutectic Al–Si alloy with improved mechanical and thermal properties by hot extrusion

Silicon phase in hypereutectic AlSi powders appears as primary Si and eutectic Si. Due to the poor thermal stability of eutectic Si, the material suffers from pores, stress concentration and dislocation packing during hot extrusion process, resulting in low density and poor thermal properties. In order to eliminate the eutectic Si, a heat treatment is conducted on Al20Si powders before hot extrusion. Because of the Ostwald ripening effect, the eutectic Si and dislocations in the powders are replaced by isolated Si lumps and a clear Al matrix. As a result, the formability and thermal properties of the material are greatly improved. The extruded samples made from the treated powder present high relative densities 99.7–100%, ultimate tensile strength (UTS) 167–170 MPa, elongations 8.8–10.8% and thermal conductivities (TCs) 191–195 Wm−1 K−1 and low coefficient of thermal expansions (CTEs) 13.8–14.5 × 10−6/K. The excellent mechanical and thermal properties are attributed to the elimination of eutectic Si from the treated powders and as-extruded alloys. In addition, hot extrusion introduces in-situ Al2O3 in the Si surface, Al grain boundary and Al grains, which is beneficial to reducing and stabilizing the CTE of the material. Moreover, it hinders Ostwald ripening and thus growth of the Si particles during the service of the material.

Wear behavior and atomic competition mechanism of flexible wear-resistant coating with oxygen-free zone in Ti6Al4V alloy

The flexible wear-resistant coating on Ti6Al4V substrate was successfully fabricated by plasma powder cladding with Al–Si powder. The microstructure, element distribution and phase component of the flexible wear-resistant coating were characterized by the field emission scanning electron microscope (FESEM), energy dispersive spectroscopy (EDS) and the X-ray diffractometer (XRD). The micro-hardness of coating was measured by micro-hardness tester. The wear-resistance of Al–Si coating was evaluated by sliding friction experiment. The prepared coatings have no cracks and a good metallurgical bonding (MB) with the substrate. The wear-resistance of the coating surface is about twice as much as that of Ti6Al4V substrate. Furthermore, the in-between MB zone has the more excellent wear-resistance (about 7 times). The oxygen free zone can be formed in the MB zone, providing a good toughness for the flexible wear-resistant coating. The wear mode is adhesive wear for the flexible wear-resistant Al–Si coatings. Based on the self-consistent bond length difference (SCBLD) method, the competition among atoms in MB zone as well as the formation mechanism of flexible oxygen free zone is investigated.

The formation of Si-aluminide coating formed by plasma spraying and subsequent diffusion annealing on Ti-Al-7Nb intermetallic alloy

In the article, the kinetic growth phenomena of aluminide coating formed by plasma spraying pure Al-Si powder and subsequent diffusion annealing on TiAl intermetallic alloy in inert atmosphere were investigated. The Al-Si powder was thermal sprayed (APS) on TiAl7Nb intermetallic alloy and annealed in Ar atmosphere during 5, 15, 30, 60, 240 and 480 min. The kinetic growth of the coating was observed using the scanning electron microscopy method (SEM), and chemical composition was analysed using the EDS method. The Kirkendall Effects pores formation, as well as titanium silicides on the grain boundary of TiAl3, was found. The oxidation resistance of the developed coating might be analysed in further work. The developed coating might be used for the production of protective aluminide coatings on TiAl intermetallic alloys. The description of aluminide coating formation in a new technological process.

Silicon alloying enhances fast heating rate combustion of aluminum particles

Alloys and composites of aluminum (Al) have shown promise in regulating and enhancing particle combustion for energy generation applications. Recent work on aluminum-silicon (Al-Si) spherical alloy particles has shown improved combustion at low heating rates through enhanced diffusion accompanying a lower melting temperature. This study extends reactivity analysis to higher heating rates, comparing oxidation of Al-Si with Al. Flame speeds of Al-Si powder mixed with molybdenum trioxide (MoO3) powder (Al-Si+MoO3) exhibited a faster transition to steady propagation relative to Al+MoO3. Bomb calorimetry experiments revealed up to 5.8% greater early temperature rise for Al-Si powder. Rapid steady propagation for Al-Si mixture and faster temperature rise for Al-Si particles were attributed to accelerated kinetics evidenced in thermal equilibrium analysis of the mixtures using a differential scanning calorimeter (DSC). Larger DSC exotherms in the early stages of oxidation (i.e., 480–720 °C) correlated with early heat release and promoted steady flame propagation for Al-Si+MoO3 compared with Al+MoO3. Furthermore, in multiple heating rate DSC studies, Al-Si+MoO3 ignited at a lower heating rate (i.e., 15 ⁰C/min) than Al+MoO3 (i.e., 20 ⁰C/min). Both mixtures ignited at temperatures less than 625 °C which is above the melting temperature of Al-Si (574 °C) and below Al (659 °C). Thus, alloy particle fuels with enhanced diffusion-controlled kinetics promote steady flame propagation and show promise for energy generation applications. This is especially promising for technologies driven by enhanced condensed phase combustion such as some propellant additives or applications dependent on reliable burn rates such as pyrotechnic time delay formulations and primers.

Architecting micron SiC particles on diamond surface to improve thermal conductivity and stability of Al/diamond composites

In this paper, a new method to synthesize micron silicon carbide (SiC) particles on the diamond surface at low temperature was proposed, namely, the micron SiC particles had been synthesized by aluminum-silicon (Al-Si) mixed powders and vacuum annealing technology. Continuity and formation mechanism of the SiC particles were studied. The continuity of the SiC particles is affected by annealing temperature and the mass fraction of silicon (Si) in Al-Si mixed powders. When the mass fraction of Si in Al-Si powders is 70 wt.% and the annealing temperature is 800°C, SiC particles with a continuous structure can be synthesized. Aluminum carbide (Al4C3) as the indispensable intermediate phase plays a crucial role in promoting the formation of SiC particles at low temperature. The Al/diamond composite with high thermal conductivity of 711 W·m−1·K−1 was obtained by introducing SiC particles with a continuous structure. Meantime, the continuous SiC layer effectively inhibited the formation of Al4C3 at the interface of the composite, and only 0.5 wt.% of Al4C3 was detected by gas chromatography. This study provides a novel practical way for surface coating engineering on diamond particles, which can be used to improve thermal conductivity and inhibit the interfacial Al4C3 of Al/diamond composites.

Structure and Phase Composition of Ti–Al–Si Powder Composites at Different Synthesis Conditions

Structure and Phase Composition of Ti–Al–Si Powder Composites at Different Synthesis Conditions

Characterizing the microstructural effect of build direction during solidification of laser-powder bed fusion of Al-Si alloys in the dilute limit: A phase-field study

Additive manufacturing experiments using the laser powder bed fusion (LPBF) method reveal that changing the build direction can stimulate morphological transitions in the solidification microstructure. As a result, the final texture and material properties can be altered. In this work, we conduct numerical investigations to explore the effect of building direction on the microstructure evolution of dilute Al-Si alloy produced by the LPBF process. A finite element thermal model is developed to incorporate the effect of build direction on the thermal characteristics of the melt pool for a vertically and horizontally printed Al-Si powder layer. We then utilize a multi-order parameter phase-field model to probe the microstructure evolution of LPBF Al-Si alloy in the dilute limit under the aforementioned thermal conditions for horizontal and vertical printing strategies. The phase-field model described here can self-consistently emulate spontaneous formation of nuclei from inoculant particles and simulate morphological transitions. The accuracy of the phase-field model is validated through the numerical examination of morphological transitions under directional solidification conditions of a dilute Al-Si alloy and compared to the predictions of the analytical CET theory of Hunt [1]. The phase-field simulations and subsequent grain analysis of the microstructure under transient thermal conditions reveal that the nucleation rate and hence equiaxed to columnar microstructure ratio is notably higher in the horizontally built samples. These results are in consistence with experimental observations.

Laser welding 6061 aluminum alloy with laser cladding powder

To solve the problem of low absorption and welding surface collapse in the laser welding of the 6061 aluminum alloy, the powder was first added to the surface of the weld by laser cladding. The effect of laser cladding powder type on the microstructure and hardness of the 6061 aluminum alloy was studied. The results show that laser cladding of single Al powder, Si powder, and Ni powder can all improve laser absorption during laser welding of aluminum alloy, but each material has specific limitations, such as reducing the number of strong phases, generating other phases, and the nonevening of phases. Two kinds of mixed powder, Al:Si and Al:Ni, can overcome these limitations to a certain extent. Laser cladding with three kinds of mixed powder resulted in a better welding effect than when using two kinds of mixed powder or a single powder. By applying an extreme vertices design, the optimum ratio of Al-Si-Ni powder was determined as 0.737:0.185:0.078, resulting in the uniform microstructure of the weld without delamination. The mechanical properties test shows that the hardness of the laser cladding with powder was better than that without laser cladding powder, and the tensile strength of the weld was 83% of the base material.

Thermal Barrier Coatings for Molybdenum Produced Using Nanopowders

The molybdenum is one of the most important refractory metals used in aerospace industry. The main disadvantage of Mo is low oxidation resistance at elevated temperature and the using of protective coatings is necessary. In present article the new types of protective coatings produced by slurry method were developed. The slurries contained Al nanopowder and Si powder as well as non-organic binder (H2CrO4 and water). After immersion and drying the samples with slurries were heat treated at 1000°C in Ar atmosphere. The thickness of obtained coatings was in range 10-20 μm. The presences of phases form Mo-Al as well Mo-Si systems was analyzed using scanning electron microscopy. The developed coatings were used as a bond coat for ceramic layer produced by plasma spray physical vapour deposition method (PS-PVD). In this process the columnar ceramic layer contains yttria stabilized zirconia (YSZ) was obtained wit thickness above 100 μm. The obtained results showed that it is possible to obtain TBC coating on molybdenum contained Al-Si bond coat and outer YSZ ceramic layer. The proposed coating can be used in aerospace applications.

Dissimilar unbeveled butt joints of AA6061 to S235 structural steel by means of standard single beam fiber laser welding-brazing

Abstract The design of parts involving the combination of different materials has gained much attention in recent years as a strategy to achieve weight reduction. Joining of dissimilar materials has become a necessity to produce such parts. However, obtaining dissimilar welds showing high mechanical performance usually takes complex, expensive and time-consuming approaches. In this study, an affordable welding approach is proposed to join 6061 aluminum alloy to S235 structural steel, based on a single laser beam, on unbeveled square butt joints, and on the combination of welding wire and preplaced Al-Si powder. The relation between welding parameters and imperfections formation is studied by using a combined parameters analysis, and thorough microstructural and mechanical characterization are performed. The application of AlSi5 wire in combination with AlSi12 powder led to crack-free welds showing homogeneous 3 ± 1 μm-thick intermetallic compound (IMC) layer, composed of Fe2Al5, Fe4Al13 and Fe4Al17.5Si1.5 intermetallics. Transverse tensile tests showed that ultimate tensile strength of joints was as high as 169 MPa, which is above the minimum value established by international standards on AA6061 welds and comparable to the values obtained by other authors’ dissimilar welds by using more complex and expensive welding approaches. The IMC layer showed 11.2 ± 0.7 GPa hardness and 257 ± 24 GPa modulus of elasticity. Both properties are much higher than the base materials ones, and are in agreement with the mechanical behavior seen under tensile testing.

Mechanical and Metallurgical Studies on Thixoextruded Al-Si Alloys

Thixoforming is a commonly known material processing technique that involves the fabrication of materials between solidus and liquidus temperatures. One of the prerequisites for this process is that the microstructure of the feedstock material must contain solid near-globular grains in a liquid matrix and a broad solidus-to-liquidus transition range. The aim of the present work is to study the application of Al-Si powder metallurgy (P/M) alloy in the thixoextrusion process and to evaluate the properties before and after extrusion. Al-Si P/M alloys were prepared for various Si compositions (1-7%) and Mg compositions (0.2-0.8%). The best among the Al-4Si and Al-4Si-0.6 Mg were selected based on hardness and density results. Differential thermal analysis revealed the solidus and liquidus temperatures to be 557 and 642 °C for Al-Si alloy and 564 and 636 °C for Al-4Si-0.6 Mg alloy, respectively. Compaction temperature and holding time studies have been carried out and the corresponding optimized parameters are found to be 550 °C and 60 min. Thixoextrusion was performed on the hot compacted preforms for three temperatures namely 560, 580 and 600 °C, respectively. An extrusion ratio of 4:1, strain rates of 0.1, 0.2 and 0.3 s−1 and die approach angle of 60° were used for the tests. Extrudates were divided into three regions namely front, middle and end parts to analyse its mechanical and metallurgical properties. Micrographic analysis revealed the presence of globular grains in the specimen. Hardness values showed a marginal increase from 45 to 60 HV for Al-4Si alloy and 42-80 HV for Al-4Si-0.6 Mg alloy.

Synergistic effect of carbon nanomaterials on a cost-effective coral-like Si/rGO composite for lithium ion battery application

The emergence and the continuous rise of smart technologies require to emergently meet their ever-increasing energy demand. Improving the commercial lithium-ion batteries (LIB) by using silicon —which has a distinct energy storage capacity— might be a promising solution. However, solving Si-related problems, such as gross volume variation and low electrical conduction, is indispensable. Preparing different Si nanostructures having certain internal voids, and adding some conductive materials, are two smart approaches largely used to mitigate the volume expansion and to enhance the electrons transport of LIB anodes. Still, their raw materials and their preparation methods are generally costly, which limits their feasibility for commercial scalability. In this study, we synthesized a coral-like nanoporous Si/rGO composite, starting from cheap raw materials (graphite and Al–Si powders), and using simple methods which do not need any high temperatures or sophisticated equipment. The preparation steps were also reduced, as the reactions of Al-etching and GO reduction concurrently occurred. The LIB half-cells made on this composite were further improved by incorporating other carbon nanomaterials which had a synergistic effect on both cycling and rate performances: a reversible capacity of 1080 mAh g− 1 at 0.2 A g− 1 after 250 cycles; and ∼1710, 1300, 1030 and 840 mAh g− 1 at a rate of 1, 2, 3, and 4 A g− 1 respectively, have been achieved. Testing a full battery with an LCO cathode has also given a promising result: a reversible capacity of ∼54 mAh g− 1 at 36 mA g− 1 after 25 cycles has been obtained.

Structure Formation and Properties of Eutectic Silumin Obtained Using Selective Laser Melting

An Al–Si eutectic alloy was synthesized by the selective laser melting (SLM) method using a pilot wrought Al-Si powder (of Russian AKD-12 grade) as the starting material. On the basis of electron microscopy, the microstructure of the SLM alloy was certified with EDS mapping of elements (Al and Si). It has been established that the main structural component is an Al-based solid solution with a cellular-dendritic structure (with an average cell size of ~500 nm). The Si phase, which is a component of the eutectic, is located at the boundaries in the form of rounded crystals about ten nanometers in size. This paper presents the results of measuring the mechanical and nanomechanical properties, which show the competitiveness of the use of the pilot (experimental) powder.

Reaction bonding alumina with AlN–SiC solid solution by nitridation of matrix containing Al–Si powders

An AlN–SiC solid solution-bonded alumina composite was successfully synthesized by pre-synthesizing an isostructural AlN mesophase as an induced nucleus at 1600 °C in flowing nitrogen. The phase composition and morphology were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The reaction mechanism is as follows. An AlN cladding is formed on the surface of Al particles by holding the Al–Si–Al2O3 green body at 580 °C for 8 h in N2 atmosphere. As the temperature rises, the AlN cladding ruptures, Al(l) flows out, and entraps the AlN fragments with high reactivity to migrate along the pores, mixing Si(l) and ultra-fine carbon from resin binder in the matrix to form an Al(l)–Si(l)–C(s)–AlN(s) mixture. At 1600 °C, Al(l) and Si(l) preferentially react with trace O2 in nitrogen to form metastable Al2O(g) and SiO(g), which diffuse outward and react with N2 in the peripheral of the brick to form a sheet-like 21R-SiAlON. The 21R-SiAlON sheets interlaced with each other, forming a dense layer. The formation of the dense layer rapidly consumes O2, and the $$P_{{{\text{O}}_{{2}} }}$$ inside the brick is lowered quickly. In such reducing condition, under the induction of the preformed AlN mesophase, the isostructural AlN–SiC solid solution is formed in situ by the reaction between Al(l)–Si(l)–C(s)–AlN(s) mixture and N2, and therefore a non-oxide bonded oxide composite is prepared. The AlN–SiC solid solution-reinforced Al2O3 composite possesses high cold crushing strength of 116–217 MPa.

Modification of matrix for magnesia material by in situ nitridation

Abstract Mg-α-SiAlON bonded periclase composites were prepared at 1550 °C in a nitrogen atmosphere using sintered magnesia particles, Al metal powder, Si powder, magnesia, and α-Al2O3 powder as raw materials and were bonded with a phenolic resin. The modification mechanism was investigated. Tabular-shaped Mg-α-SiAlON can be obtained through the diffusion-reaction-dissolution-precipitation mass transfer mechanism. It was found that modification of the matrix for the magnesia material led to a direct bonding mode and a card structure. The optimal percentage of powder material was determined to be 40 wt%, by which a well-developed card structure was obtained. The sintered Mg-α-SiAlON bonded periclase composites exhibited excellent cold modulus of rupture (12.5 MPa), and the residual strength retention rate was 3 times higher than that of a magnesia specimen after the third thermal shock. The enhanced thermal shock resistance was attributed to a lower thermal expansion coefficient and the “crack deflection” mechanism of tabular-shaped Mg-α-SiAlON.

Metal injection moulding (MIM) as an alternative fabrication process for the production of TWIP steel

ABSTRACTTwinning Induced Plasticity (TWIP) steels are high manganese austenitic steels that have caused growing interest over the last decade due to their unique combination of strength and elongation. Nevertheless, the problems presented during their current fabrication process (continuous casting) complicate their production and commercialisation. Powder metallurgy may be an attractive alternative route of solving these problems in certain components. In this work, Metal Injection Moulding (MIM) is explored as an alternative fabrication method for TWIP steels, having the additional benefit of reaching a near-theoretical densification. The feedstock of this study is composed of a metallic prealloyed Fe–Mn–C–Al–Si powder and a binder system based on wax-HDPE. The feedstock was optimised by examining different metallic loads. A suitable powder–binder ratio was determined based on mixing torque and melt flow index measurements. It was optimised a two-stage debinding process and a sintering process in an argon atmosphere to obtain the correct microstructure.

Microstructure and properties of Al-60wt.%Si composites prepared by powder semi-solid squeeze

Al-60wt.%Si composites were successfully prepared by semi-solid squeezing powder mixture of Al and Si at 700 °C. The appearance of about 50wt.% Al-Si metal liquid results that less than 4–5 MPa pressure can squeeze the Al-Si powder mixture to near full density at vacuum condition. The effects of Si particle size on the microstructure and properties of Al-60wt.%Si were investigated. The results show that the composites are consisted of only Si and Al. Si particles distribute evenly in aluminum matrix. Al matrix exhibits a certain preferred orientation under the condition of directional solidification. Si particles with 5 μm size tend to be aggregated into locally interconnected particles and can be effectively passivated. As Si particle size ranges from 10 to 20 μm, the corner passivation effect for Si particles is gradually suppressed. The fracture morphology of Al-60wt.%Si is composed of cleavage platforms of Si grains and fine tearing ridges of Al which tightly wraps Si grains. With the increase of Si particle size from 5 to 20 μm, the flexural strength of Al-60wt.%Si decreases from 270 MPa to 223 MPa, the thermal conductivity increase from 128 to 136 W·m−1·°C−1, and the average coefficient of thermal expansion from ambient temperature to 400 °C ranges from 9.49 to 9.97 × 10−6 °C−1.

Research about Titanium Alloyed Layer’s Temperature Oxidation Resistance on Aircraft Engine Surface

Aircraft engines often work in a high temperature or easily oxidized environment, and the titanium alloy layer on the surface of the existing aircraft engine is poorly resistant to high temperature oxidation. The maximum temperature that can bear currently is slightly above 500°C, which severely limits its widespread application. In order to improve its resistance ability to high temperature oxidation, laser surface alloying technique was adopted here which Ti-Al-xSi alloying layer was prepared on the surface of matrix Ti-6Al-4V alloy (It is mainly composed of Ti-Al Intermetallic Compound and Ti5Si3 Reinforced Phase) and the analysis were presented in three aspects: material phase, tissue observation and high temperature oxidation resistance ability during different time periods. The experimental data of tissue composition, structure and high temperature oxidation resistance of Ti-al-xsi alloying layer which was preset different proportion of Al powder and Si powder mixture were compared. The experimental results showed that, when the mass of Si powder was 10%, 20% and 30% of the Al powder mass, Ti-Al Intermetallic Compound has evolved from TiAl to TiAl2 phase and TiAl3 phase with the increasing additive amount of Si, which had excellent oxidation resistance at high temperature. At the same time, the oxidation weight of alloying layer was decreased and the oxidation rate was declined.

Microstructure evolution and interface structure of Al-40 wt% Si composites produced by high-energy ball milling

High silicon content Al-Si composites with a composition of Al-40 wt% Si were fabricated via a high-energy ball milling method. The microstructure evolution of Al-40 wt% Si milled powders and sintered composites has been thoroughly studied by scanning electron microscopy, X-ray diffraction, energy-dispersive spectrometry and high-resolution transmission electron microscopy. The mechanism of ball milling Al-40 wt% Si powders has been disclosed in detail: fracture mechanism dominating in the early stages, followed by the agglomeration mechanism, finally reaching the balance between the fragments and the agglomerates. It has been found that the average particle sizes of mixed Al-Si powders can be refined to the nanoscale, and the crystallite sizes of Al and Si have been reduced to 10 nm and 62 nm upon milling for 2 h–50 h, respectively. The finally formed Al-Si interfaces after ball milling for 50 h are well-cohesive. A dense and homogenous Al-40 wt% Si composite have been achieved by solid-state sintering at 550 °C. The results thus provide an effective support for producing bulk nanostructured Al-Si composites.