Unreinforced Matrix Alloy Research Articles

A Study on the Optimization of Nano-B4C Content for the Best Wear and Corrosion Properties of the Al-Based Hybrid Nanocomposites

This investigation is dedicated to producing hybrid nanocomposites based on AA2024, achieved through the utilization of powder metallurgy methods encompassing mechanical milling and hot pressing. The research focused on studying how changes in B4C content influence the mechanical, wear, and corrosion behavior of AA2024/h-BN/B4C hybrid nanocomposites. The findings revealed that as the B4C content increased, the relative density values decreased, and higher porosity values were observed in the hybrid nanocomposite samples. Among the tested samples, the hybrid nanocomposite with 4 wt% B4C exhibited the most favorable properties. It demonstrated significantly higher hardness and ultimate tensile strength compared to AA2024 matrix alloy, with values of 161 HB and 372 MPa, respectively. In contrast, the matrix alloy showed hardness and ultimate tensile strength values of 105 HB and 237 MPa, respectively. Furthermore, the wear resistance of hybrid nanocomposite with 4 wt% B4C displayed approximately 14 times greater wear resistance under 40 N load compared to the unreinforced AA2024 matrix alloy. The corrosion test results have revealed that the corrosion resistance of the hybrid nanocomposite reinforced with 4wt% B4C is nearly 47% higher compared to the corrosion resistance of the unreinforced AA2024 alloy. This nanocomposite exhibits the highest polarization resistance of 5.21 Ω.cm2.

Microstructure and Mechanical Properties of the EN AC-AlSi12CuNiMg Alloy and AlSi Composite Reinforced with SiC Particles

There is growing interest in developing more advanced materials, as conventional materials are unable to meet the demands of the automotive, aerospace, and military industries. To meet the needs of these sectors, the use of advanced materials with superior properties, such as metal matrix composites, is essential. This paper discusses the evaluation of microstructural and mechanical properties of conventional eutectic EN AC-AlSi12CuNiMg aluminum alloy (AlSi12) and advanced composite based on EN AC-AlSi12CuNiMg alloy matrix with 10 wt% SiC particle reinforcement (AlSi12/10SiCp). The microstructure of these materials was investigated with the help of metallographic techniques, specifically using a light microscope (LM) and a scanning electron microscope (SEM). The results of the microstructural analysis show that the SiC particles are uniformly distributed in the matrix. The results of the mechanical tests indicate that the tensile properties and hardness of the AlSi12/10SiCp composite are significantly higher than those of the unreinforced eutectic alloy. For AlSi12/10SiCp composite, the tensile strength is 21% higher, the yield strength is 16% higher, the modulus of elasticity is 20% higher, and the hardness is 11% higher than unreinforced matrix alloy. However, the unreinforced AlSi12 alloy has a percentage elongation that is 16% higher than the composite material. This shows that the AlSi12/10SiCp composite has a lower ductility than the unreinforced AlSi12 alloy. The tensile specimens of the tested composite broke apart in a brittle manner with no discernible neck development, in contrast to the matrix specimens, which broke apart in a ductile manner with very little discernible neck formation.

Tribological Behavior of Cast Aluminum Matrix Composites After Multiple Remelting

One of the limiting factors for expanding the applications of aluminum alloy castings in many high-tech industries is the insufficient level of tribological properties, especially under conditions of dry and abrasive wear. Reinforcing of aluminum alloys with hard ceramic particles, i.e., transition to aluminum matrix composites, allows significantly increasing their resistance against dry sliding friction, scuffing, and seizure in wide temperature and force intervals of operation. Among the numerous problems related to the industrial implementation of cast aluminum matrix composites, the problem of their recycling takes the important place. This work is aimed at establishing the influence of metallurgical processes during remelting on the change in tribological properties of cast Al-Si-B4C aluminum matrix composites. For this purpose, tribological tests in conditions of dry friction according to the ball-on-disc scheme were used. Reinforcing of an AlSi12 matrix alloy with B4C particles leads to a decrease in the composite friction coefficient and the mass wear in the as-cast state in comparison with an unreinforced matrix alloy. During remelting, the tribological properties of the aluminum matrix composites do not deteriorate. Repeated remelting leads to the improvement in particle distribution uniformity, formation of the Al3BC phase at the matrix/particle interfaces, fragmentation of reinforcing B4C particles due to cyclic thermal loads as well as an increase in the porosity fraction. The changes in the structural-phase composition during remelting have a direct influence on the level of tribological properties. Typical effects associated with dry friction, such as plastic deformation of the matrix material and the formation of areas of adhesion-cohesive fracture, indicative of scuffing, were revealed by SEM analysis of the wear tracks of an unreinforced matrix alloy. For the composite material, these effects manifested to a much lesser extent. A qualitatively similar sliding wear behavior was observed for all composite samples, regardless of the remelting iteration. The study suggests that the formation of a transitional tribolayer may occur during dry sliding friction of aluminum matrix composites, which can reduce the friction coefficient.

A study on the improvement of wear and corrosion properties of ZA40/Graphene/B4C hybrid nanocomposites

The objective of the study was to investigate the production and evaluation of ZA40/Graphene/B4C hybrid nanocomposite (HNC). To fabricate the HNC powders (HNPs) involved the combination of graphene nanoplatelets and B4C micro-particles with ZA40 powders through mechanical milling. The graphene content remained constant 1 wt%, while the B4C content varied at 1 wt%, 2 wt%, and 3 wt%. After an 8-hour milling process, the HNPs were subjected to hot-pressing to create bulk HNC samples. Various tests, including microstructural analysis, hardness, tensile strength, wear resistance, and corrosion resistance, were conducted on the consolidated samples. The results indicated that the HNC sample containing 3 wt% B4C (S3) exhibited the most favorable properties. This sample displayed a hardness value of 181 HB, significantly higher than the ZA40 matrix alloy's hardness of 133 HB. Moreover, its ultimate tensile strength measured at 243 MPa, which was much higher than the ZA40 matrix alloy (157 MPa). The wear resistance of HNCs increased significantly with an increase in B4C content. The sample containing 3 wt% B4C demonstrated approximately 3.5 times greater corrosion resistance than the unreinforced ZA40 matrix alloy.

Different Types of Particle Effects in Creep Tests of CoCrFeNiMn High-Entropy Alloy.

Compressive creep tests were performed on a CoCrFeNiMn equiatomic alloy with the dispersion of (i) aluminum nitride or (ii) boron nitride at temperatures of 973 K and 1073 K. The results are compared with previously published creep rates of the unreinforced matrix alloy and the alloy when strengthened by yttrium + titanium oxides. The comparison reveals that the creep rate is essentially unchanged by the presence of aluminum nitride particles, whereas it is reduced by the presence of oxide particles. Boron nitride particles do not influence the creep rate at low stresses but reduce it substantially at high stresses.

Microstructure and Mechanical Properties of Hybrid AZ91 Magnesium Matrix Composite with Ti and SiC Particles.

In this paper, a new hybrid metal matrix composite, named AZ91/(SiC + Ti)p, is presented. The commercial AZ91 magnesium alloy was chosen as the matrix. The composite was reinforced with both SiC and Ti particles. The investigated material was successfully fabricated using stir casting methods. Microstructure analyses were carried out by digital and scanning electron microscopy with an energy-dispersive X-ray spectrometer (SEM + EDX). Detailed investigations disclosed the presence (besides the reinforced particles) of primary dendrites of the α phase, α + γ eutectic and some part of discontinuous precipitates of the γ phase in the composite microstructure. The composite was characterised by uniform distribution of the Ti particles, whereas the SiC particles were revealed inside the primary dendrites of the α phase, on the Ti particles and in the interdendritic regions as a mixture with the α + γ eutectic. Both the tensile and compression strength as well as the yield strength of the composite were examined in both uniaxial tensile and compression tests at room temperature. The fabricated AZ91/(SiC + Ti)p hybrid composite exhibited higher mechanical properties of all those investigated in comparison with the unreinforced AZ91 matrix alloy (cast in the same conditions). Additionally, analyses of the fracture surfaces of the AZ91/(SiC + Ti)p hybrid composite carried out using scanning electron microscopy (SEM + EDX) were presented.

Corrosion and microstructure of as-cast magnesium alloy AM60-based hybrid nanocomposite

ABSTRACT Two types of Mg alloy AM60-based composites containing (1) only 7 vol.% Al2O3 Fibre and (2) both 7 vol.% Al2O3 Fibre + 3 vol.% Al2O3 nano-Particle, named 7FC and MHNC-7F3NP, respectively, as well as the unreinforced matrix alloy AM60 were prepared by using the preform-squeeze casting technique. The microstructure of the matrix alloy AM60 characterised by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) consisted of primary α-Mg grains, eutectic β-Mg17Al12 phases and Al-Mn intermetallics, of which distribution were different from those in the composites. The reinforcement introduction refined the matrix grain structure of the composites significantly. The corrosion behaviours of the 7FC and MHNC-7F3NP composites and the matrix alloy were investigated by using the potential-dynamic polarisation test in 3.5 wt.% NaCl aqueous solution. Compared with the matrix alloy, the introduction of micron-sized alumina fibres decreased the corrosion resistance of the matrix alloy AM60 considerably due to the presence of excessive interfaces, while the high density of grain boundaries and the absence of noble precipitates such as β-Mg17Al12 phases and Al-Mn intermetallics at the grain boundaries in the composites should also be somewhat responsible for their poor corrosion resistance. The addition of the nano-sized particles led to almost no further reduction in the corrosion resistance of the MHNC-7F3NP.

Experimental study on low‐cycle fatigue behaviours of the specimen consisting of the composites (Al‐12Si/ABOw) and matrix Al‐12Si alloys

AbstractThe low‐cycle fatigue tests of the specimen, which was composed of half composites reinforced by aluminium borate whisker (ABOw) and half unreinforced matrix alloys, were performed under different temperatures. The results showed that the specimen exhibited obvious cyclic hardening at low temperature while increasingly remarkable cyclic softening with the increase of temperature. Meanwhile, the micromorphology of the fracture surface revealed apparent brittle characteristics at low temperature but dominated ductile characteristics at high temperature. The analysis of curves of total strain amplitude versus fatigue life indicated that the dominant fatigue damage mechanism changed from the elastic damage to the plastic damage with the increase of total strain amplitude. In addition, the description of fatigue behaviours based on energy criterion suggested that the capacities of specimen to absorb and dissipate plastic strain energy improved with increasing of temperature but may also be weakened by the strengthening effect of composite part.

Two-Body Abrasive Wear Behaviour of In-Situ Al-TiC Particle Composites: Influence of TiC Reinforcement and Content in the Alloy Matrix and Experimental Parameters

This study pertains to observations made on the abrasive wear response of Al-TiC composites under varying applied load and traversal distance conditions. The influence of TiC particle reinforcement and its content in the matrix on the abrasion characteristics of the samples was investigated. The composites were prepared by generating the reinforcement phase (TiC particles) from within the matrix employing a hybrid in-situ technique consisting of a combination of steps involved in powder and liquid metallurgy routes of synthesizing metal matrix composites. The unreinforced matrix alloy (AA2014) was also tested under identical experimental conditions for comparison purposes. Properties characterized were wear rate, frictional heating and friction coefficient. Microstructural features of the samples and characteristics of wear surfaces, subsurface regions and abrasive medium have also been examined.
 
 The TiC reinforcement led to improved abrasion resistance (inverse of wear rate), the degree of improvement increasing further with the rising concentration of the TiC particles in the alloy matrix. Increasing applied load led to deterioration in the wear behaviour of the samples while a reverse trend was followed as the traversal distance was raised. The severity of frictional heating was noted to increase with load. On the contrary, friction coefficient tended to decrease with increasing load except for the composite containing the highest concentration of TiC wherein a reverse trend was noticed. Both frictional heating and friction coefficient increased sharply with traversal distance initially. This was followed by a reduction in the rate of temperature increase at longer traversal distances whereas friction coefficient was observed to attain steady state condition after showing a decrease in some cases. The presence of TiC reinforcement in the alloy matrix and its increasing content led to a decrease in the friction coefficient and the severity of frictional heating. The observed wear behaviour has been substantiated through the characteristics of abraded surfaces and subsurface regions of the samples and degradation of the abrasive medium. Operating material removal mechanisms have also been examined.

Tension and fatigue behavior of Al-2124A/SiC-particulate metal matrix composites

The tension and fatigue properties of SupremEX® 225XE composites (Al-2124A/25%/SiCp/3 μm) were determined for extruded samples tested in the longitudinal orientation in the T4 condition. Tension testing was conducted at 0.001/sec on as-machined cylindrical samples tested with high alignment fixtures according to ASTM E−8. The fatigue tests were conducted on polished hourglass fatigue samples with stress ratio R = 0.1 and test frequency of 20 Hz using hydraulic grips on a Model 810 MTS servo-hydraulic testing machine according to ASTM E466-15. A total of 26 samples were tested with stress levels between 448 MPa and 557 MPa. The resulting stress vs. cycles to failure (i.e. S-N) curve was compared to the unreinforced matrix alloy, other unreinforced high strength aerospace aluminum alloys, as well as other conventionally processed MMCs. The SupremEX® 225XE MMC exhibited improvements to both the low cycle fatigue (LCF) and high cycle fatigue (HCF) performance compared to these materials. The fatigue strength at 107 cycles was 448 MPa, well in excess of those for monolithic aluminum alloys as well as conventionally processed MMCs. Detailed fractography revealed the presence of a unique cone-shaped fracture feature for samples failing in HCF. Calculations based on fracture morphologies suggested catastrophic fatigue fracture occurred as the material reached its critical fracture toughness. Initial modeling of this fatigue performance used a variant of the Universal Slopes Criterion proposed in early work at Case Western Reserve University by S. M. Manson.

Effect of nano alumina content on corrosion behavior and microstructure of Za27/graphite/alumina hybrid nanocomposites

In this study, the effect of the addition of nano-graphite and nano-alumina particles on the corrosion behavior and microstructures of ZA27 matrix hybrid nanocomposites (HNCs) was investigated. ZA27 based HNC powders were produced using mechanical milling method to obtain close homogenous distribution of the reinforcement particles in ZA27 matrix followed by hot pressing technique. Before and after corrosion tests, the microstructures of these nanocomposites were characterized using a scanning electron microscope (SEM). The corrosion behavior of hybrid nanocomposites was assessed using potentiodynamic polarization scans in 3.5% NaCl solution. The corrosion experiment results indicate that corrosion rate (85.5 mpy) of ZA27/2 vol% Al2O3-1 vol% Graphite were much higher than that of ZA27 matrix (345.5 mpy) and ZA27/1 vol% Al2O3-1 vol% Graphite nano composite (104.2 mpy). HNCs with 1%vol. nano-graphite and 2%vol. nano-alumina showed about four times higher corrosion resistance than unreinforced ZA27 matrix alloy. An increase in the corrosion rate was discussed in relation to the nano size reinforcement and porosity contents. The results showed that higher reinforcement and porosity content had an adverse effect on the corrosion behavior of hybrid nanocomposites.

Effect of reinforcement spatial distribution on mechanical properties of MgO/ZK60 nanocomposites by powder metallurgy

0.5 vol% MgO/ZK60 nanocomposites with two reinforcement arrays were successfully fabricated by a conventional powder metallurgy technique. Specifically, the combination of powder oxidization and extrusion consolidation was used to obtain a composite microstructure that was characterized by fiber-like MgO rich bands embedded in an ultrafine-grained Mg matrix. Meanwhile, a homogeneous microstructure containing MgO nanodispersoids throughout the matrix was also achieved by introducing an extra high-energy ball milling. Compared with the unreinforced matrix alloy, both nanocomposites exhibited improved strength and marginally reduced elongations. Furthermore, the homogeneous nanocomposite showed a higher strength than that of inhomogeneous counterpart. Quantitative analysis indicated that fiber-like MgO rich bands only acted as load-carrying units and nanodispersoids activated multiple strengthening mechanisms which involved grain refinement, Orowan and dislocation strengthening.

Tribological Properties of AlSi12-Al₂O₃ Interpenetrating Composite Layers in Comparison with Unreinforced Matrix Alloy.

Alumina–Aluminum composites with interpenetrating network structures are a new class of advanced materials with potentially better properties than composites reinforced by particles or fibers. Local casting reinforcement was proposed to take into account problems with the machinability of this type of materials and the shaping of the finished products. The centrifugal infiltration process fabricated composite castings in the form of locally reinforced shafts. The main objective of the research presented in this work was to compare the tribological properties (friction coefficient, wear resistance) of AlSi12/Al2O3 interpenetrating composite layers with unreinforced AlSi12 matrix areas. Profilometric tests enabled both quantitative and qualitative analyses of the wear trace that formed on investigated surfaces. It has been shown that interpenetrating composite layers are characterized by lower and more stable coefficients of friction (μ), as well as higher wear resistance than unreinforced matrix areas. At the present stage, the study confirmed that the tribological properties of the composite layers depend on the spatial structure of the ceramic reinforcement, and primarily the volume and size of alumina foam cells.

The influence of Ti particles on microstructure and mechanical properties of Mg-5Al-5RE matrix alloy composite

A new composite based on the AME505 experimental matrix alloy with Ti particles was presented. The experimental magnesium alloy with 5 wt% aluminium and 5 wt% rare earth elements (RE) (called AME505) was chosen as the matrix alloy. The composite was fabricated by the stir-casting method with 30 wt% pure spherical Ti particles. Microstructure analyses were carried out by light microscopy, XRD, scanning and transmission electron microscopy. The fabricated composite was characterized by uniform distribution of the Ti particles within the matrix alloy. The composite microstructure was composed mainly of α-Mg and Al11RE3 phases but also revealed a higher volume fraction of Al2RE phases than the unreinforced matrix alloy cast in the same conditions. This phase was located on the Ti particles which indicated heterogeneous nucleation of Al2RE on the reinforcement. The tensile and compression strength as well as yield strength of the composite were examined in both uniaxial tensile and compression tests. Additionally the Brinell hardness was determined. The composite exhibited higher examined mechanical properties in comparison the pure AME505 matrix alloy. The role of both the Ti particles and phase composition of the matrix alloy on composite behaviour was also analysed.

Superior high creep resistance of in situ nano-sized TiCx/Al-Cu-Mg composite

The tensile creep behavior of Al-Cu-Mg alloy and its composite containing in situ nano-sized TiCx were explored at temperatures of 493 K, 533 K and 573 K with the applied stresses in the range of 40 to 100 MPa. The composite reinforced by nano-sized TiCx particles exhibited excellent creep resistance ability, which was about 4–15 times higher than those of the unreinforced matrix alloy. The stress exponent of 5 was noticed for both Al-Cu-Mg alloy and its composite, which suggested that their creep behavior was related to dislocation climb mechanism. During deformation at elevated temperatures, the enhanced creep resistance of the composite was mainly attributed to two aspects: (a) Orowan strengthening and grain boundary (GB) strengthening induced by nano-sized TiCx particles, (b) θ′ and S′ precipitates strengthening.

Influence of Applied Load on Abrasive Wear Depth of Hybrid Gr/SiC/Al–Mg–Si Composites in a Two-Body Condition

The influence of load applied on wear depth of stir cast hybrid Gr/SiC/Al 6082 composites in a two-body abrasion was investigated in as cast (AC) and T6 heat-treated condition (T6). The obtained results were compared with its unreinforced alloy and SiC/Al 6082 composites. The parameters of the applied load (5–15 N), grit size (100 μm and 200 μm), and sliding distance of 75 m were used in this study. At 200-μm grit size, the wear depth of hybrid composites with respect to unreinforced matrix alloy was reduced by 38.1% (at 5 N load) and 16.2% (at 15 N load) in AC condition; 25.1% (at 5 N load), and 27% (at 15 N load) in T6 condition. The wear mechanisms were demonstrated through the analysis of wear surfaces.

Spark plasma sintering of graphitized multi-walled carbon nanotube reinforced Ti6Al4V

Graphitized multi-walled carbon nanotubes (MWCNTGr) reinforced Ti6Al4V (Ti64) matrix composites prepared via the powder metallurgy route were synthesized by spark plasma sintering (SPS) technique. 1, 2 and 3wt% MWCNTGr were dispersed in the Ti64 matrices by adapted high energy ball milling (HEBMA). Composite powder mixtures were sintered in vacuum at constant applied pressure, heating rate and isothermal holding time of 50MPa, 100°C/min and 5min respectively. The sintering temperature was varied between 850 and 1000°C. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize the as-received MWCNTs, MWCNTGr, admixed composite powders and the bulk sintered composites. MWCNTGr evolution during graphitization treatment, dispersion in Ti64 matrix and in the sintered composites was analyzed using the characteristic Raman peak intensity ratio (ID/IG). The relative density of the sintered MWCNTGr/Ti64 composites was enhanced with increased sintering temperature, but deteriorated with increased wt% MWCNTGr in the metal matrix. Vickers microhardness of the consolidated composites improved with increasing sintering temperature and weight fractions of MWCNTGr over that of the unreinforced matrix alloy. The formation of crystalline TiC interfacial product during composite powder processing and consolidation is also discussed.

Effect of applied pressure on high-stress abrasive wear behavior of hybrid Al–Mg–Si composites

In this experimental investigation, the effect of applied pressure on high-stress abrasive wear resistance characteristics of stir-cast Al 6082-5 wt% SiC-5 wt%Gr (Al–SiC–Gr) hybrid metal matrix composites was studied and compared with its unreinforced matrix alloy and 10 wt% SiC-reinforced (Al–SiC) composites. The tests were carried on pin-on-disc equipment at applied pressures of 0.1–0.3 MPa, sliding distance of 75 m, and SiC abrasive grit size of 100 µm and 200 µm. It was noted that the wear resistance decreases with increase in applied pressure in both as-cast and T6 conditions. The improvement in wear resistance was 1.63 (alloy) to 3.29 m/mm3 (Al–SiC–Gr) in case of lower grit size and applied pressures. However, the marginal improvement of wear resistance was observed i.e. 0.67 (alloy) to 1.05 m/mm3 (Al–SiC–Gr) at higher grit size and applied pressures. Relative wear resistance plots indicate that hybrid composites conceded better wear resistance properties compared to SiC-reinforced composites. The evaluation of wear mechanisms, worn surfaces of the pins, emery papers, and debris was also studied using scanning electron microscopy.

Synthesis, characterization and properties of stir cast AA6351-aluminium nitride (AlN) composites

Abstract

Dry sliding wear of heat treated hybrid metal matrix composites

In recent years, there has been an ever-increasing demand for enhancing mechanical properties of Aluminum Matrix Composites (AMCs), which are finding wide applications in the field of aerospace, automobile, defence etc,. Among all available aluminium alloys, Al6061 is extensively used owing to its excellent wear resistance and ease of processing. Newer techniques of improving the hardness and wear resistance of Al6061 by dispersing an appropriate mixture of hard ceramic powder and whiskers in the aluminium alloy are gaining popularity. The conventional aluminium based composites possess only one type of reinforcements. Addition of hard reinforcements such as silicon carbide, alumina, titanium carbide, improves hardness, strength and wear resistance of the composites. However, these composites possessing hard reinforcement do posses several problems during their machining operation. AMCs reinforced with particles of Gr have been reported to be possessing better wear characteristics owing to the reduced wear because of formation of a thin layer of Gr particles, which prevents metal to metal contact of the sliding surfaces. Further, heat treatment has a profound influence on mechanical properties of heat treatable aluminium alloys and its composites. For a solutionising temperature of 5500C, solutionising duration of 1hr, ageing temperature of 1750C, quenching media and ageing duration significantly alters mechanical properties of both aluminium alloy and its composites. In the light of the above, the present paper aims at developing aluminium based hybrid metal matrix composites containing both silicon carbide and graphite and characterize their mechanical properties by subjecting it to heat treatment. Results indicate that increase of graphite content increases wear resistance of hybrid composites reinforced with constant SiC reinforcement. Further heat treatment has a profound influence on the wear resistance of the matrix alloy as well as its hybrid composites. For all the heat treatment processes studied ice quenching with ageing duration of 6hrs resulted in improved wear resistance of both the unreinforced matrix alloy and its hybrid composites.