Al Matrix Composites Research Articles

Effect of Al2O3 particle content on microstructure and mechanical properties of 1060Al/Al–Al2O3 composites fabricated by cold spraying and accumulative roll bonding

1060Al/Al–Al2O3 laminated particle-reinforced aluminum matrix composites (LPRAMCs) were successfully prepared using a combination of cold spraying (CS) and accumulative roll bonding (ARB) techniques, exhibiting a synergistic improvement in strength and plasticity. The effects of Al2O3 particle content on the microstructure, tensile properties and fracture morphology of LPRAMCs were studied. The results showed that compared with the 1# composites with higher Al2O3 particle content (20.1 vol%), the 2# composites with lower Al2O3 particle content (8.4 vol%) exhibited delayed necking fracture during the ARB process, with greater elongation (El) but lower ultimate tensile strength (UTS). After 5 passes of ARB, the UTS and El of the 1# and 2# composites were 345 MPa, 16.1%, and 293 MPa, 22.2%, respectively. This suggests that the mechanical properties of the Al–Al2O3 deposited layer have a significant impact on the mechanical properties of LPRAMCs. With an increase in ARB passes, the fracture mode of the LPRAMCs shifted from brittle to ductile fracture, displayed by equiaxed and shear dimples. These findings can provide novel insights and theoretical foundations for optimizing the mechanical properties of Al matrix composites.

Structure and properties of fine diameter continuous SiC ceramic fiber reinforced Al matrix composites

The polymer-derived-SiC ceramic fibers reinforced 7075 aluminum alloy composites were prepared by hot pressing method. The effect of an in-situ carbon coating on the fiber surface was investigated. The results showed that the uncoated SiC fibers reacted with the Al matrix after hot pressing at 630 °C for 6h. The interfacial bonding was too strong to deflect micro-cracks, leading to a pseudo-brittle fracture with a flexural strength of only 170.7 MPa. When an in-situ carbon coating of 400 nm was prepared on each SiC fiber, the carbon coating reacted with the Al matrix instead of the SiC fiber to form a complex multi-layer interface of 160 nm. The composite had an enhanced strength of 879 MPa. When heat treatment in air, the interfacial bonding strength of the two composites both gradually decreased, making the fracture mode and mechanical properties change finally.

Enhancing mechanical properties of Al matrix composites via porous reduced graphene oxide strengthened interface

Defective graphene can effectively improve the interface between graphene and Al matrix. To further improve the interface bonding between graphene reinforcement and Al matrix, chemical etching was proposed to generate nanopore defects on surface of graphene oxide (GO), forming porous reduced graphene oxide (P-RGO) reinforcement. P-RGO/Al hierarchical composites were prepared by electrostatic adsorption, ball milling, and spark plasma sintering. "P-RGO rich zones" were formed via uniformly distributing P-RGO into Al matrix, and thus a hierarchical structure consisting of "P-RGO rich zones" and "P-RGO free zones" was constructed. The results show that ultimate tensile strength (UTS, 339.8 MPa), yield strength (YS, 296.1 MPa), and elongation (εf, 9.1 %) of P-RGO/Al hierarchical composites were 23.1 %, 78.1 %, and 9.6 % higher than those of GO/Al composites. Nanopore defects increased specific surface area of P-RGO and provided nucleation sites for the interfacial reaction. Al2O3 formed in situ at the nanopores and Al12Mg17 precipitated at the interface together improved the interfacial bonding and enhanced the load transfer. The hierarchical configuration established by "P-RGO rich zones" and "P-RGO free zones" arranged alternately in space promotes crack deflection and increases crack propagation path. This work provides a promising way for the fabrication of high-performance composites.

The effect of electrospinning time on the structure and mechanical properties of TiO2 continuous nanofibers reinforced aluminum matrix composites

This study was conducted to fabricate aluminum (Al) matrix composites reinforced with titanium oxide (TiO2) continuous nanofibers to study their mechanical properties. For this aim, the solution containing polyvinyl acetate, dimethylacetamide, acetic acid, and titanium isopropoxide was electrospun over an Al layer at different times of 1, 3, 5, 10, and 20 min. After heat treatment at 500 °C, sheets containing nanofibers were sintered and connected together by the hot pressing at 625 °C. The characterizing of the nanofibers and composites was performed using Transmission electron microscope (TEM), Atomic force microscope (AFM), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) equipped with Energy-dispersive X-ray spectroscopy (EDS) analysis to evident the TiO2 nanofibers morphology and their distribution in the Al matrix. The mechanical properties of composites produced with different electrospinning times were studied. The results showed that maximum yield and tensile strength (about 98% and 62% increase compared to Al matrix, respectively) and toughness were obtained in the composites with electrospinning times of 3 and 5 min. Additionally, it was found that the composites hardness was continuously increased by increasing the time of electrospinning (almost 44% more than the Al matrix). However, the tensile and toughness values were decreased in the composites with more increasing the amount of TiO2 nanofibers at electrospinning times of about 10 min and 20 min. Fracture surface results showed that the presence of large aggregates, breakage of TiO2 nanofibers, and weak bonding between the Al sheets were the effective factors in the decrease of mechanical properties of these composites at more electrospinning times.

Effect of aging treatment on microstructure and mechanical properties of Al matrix composite reinforced by in-situ intragranular Al2O3

Age-hardening Al matrix composites (AMCs) exhibit great potential for developing advanced metal structural materials, while reinforcement configuration-dependent aging behaviors are still largely unclear. To gain an in-depth fundamental understanding of the effect of in-situ generated intragranular reinforcement on precipitation response, a systematical heat-treatment was applied for the in-situ generated Al2O3 reinforced AlCu composite prepared via powder metallurgical Al-5 wt% CuO (Al-5CuO) system. Results show that the nano-scale intragranular Al2O3 activates the dislocation-assisted bulk diffusion pattern to promote the precipitation response, thus effectively shortening the peak-aging time of the composite as compared to the referenced Al-4 wt% Cu alloy matrix (Al4Cu). The adequate precipitation within grains in the early-aging stage endows the peak-aged Al-5CuO composite with homogeneous size distribution of θ’ phase, contributing to the impressive mechanical properties. The mechanical analyses reveal that precipitation strengthening accounts for the prominent elevation of yield strength, while the enhanced ductility is achieved by decreasing the size and number density of precipitates segregated along reinforcement-matrix interface and grain boundary. This work yields new insights into intragranular reinforcement-driven precipitation response, which is crucial for designing age-hardening AMCs with high mechanical performance.

A Model for Direct Effect of Graphene on Mechanical Property of Al Matrix Composite

Direct effect of graphene on mechanical property of Al matrix composite has been studied by using molecular dynamic (MD) methods. The models of graphene-reinforced composite are achieved by modeling the sintering system consisting of Al particles and graphene nanosheets (GNSs), while pure Al models are obtained by deleting graphene in the composites. Structural analysis on composites indicate the increment of GNSs can promote the densification of metal matrix, increase the porosity in composite, and restrict the metal grain size. Such analysis is also performed on pure Al models, and the similarity in structure between pure Al and composite models is confirmed by the tiny difference in the nanopores, atomic images, and the number of ordered atoms. Tensile processes on the similar structures with or without graphene reveal that the direct effect of graphene shows an obvious anisotropy, low graphene content may weaken the composite in some directions, while high graphene content can strengthen the composite in more directions. However, the highest content of GNSs just brings a slight increase of 2.7% in tensile strength. The atomic images of crack propagation and the atomic stress confirm that graphene is not efficient in load transfer. Therefore, the direct effect of graphene is believed to play a very small role in strengthening mechanisms.

Reinforcing Al matrix composites by novel intermetallic/SiC interface and transition structure

Interfacial bonding has attracted extensive attention because it essentially affects the performance of SiC reinforced Al matrix composites. To investigate the impact of Ni and Cu inherent in the Al matrix on the interfacial bonding of the composite, Al–Si–Mg/oxidized SiC composite and Al–Si–Cu–Ni–Mg/unoxidized SiC composite were fabricated by semisolid stir casting. Our study demonstrated that several intermetallics can nucleate and grow on the surface of SiC in Al–Si–Cu–Ni–Mg/unoxidized SiC composite during solidification, forming the intermetallic/unoxidized SiC interface and Al-intermetallic-SiC transition structure. The bonding of the Al3CuNi/unoxidized SiC interface is stronger than the conventional Al/oxidized SiC interface. The Al3CuNi/unoxidized SiC interface is functional in impeding crack propagation and withstanding loading during deformation. Moreover, the Al-intermetallic-SiC transition structure can alleviate the agglomeration of SiC particles, improve the overall coherency and coordinate the deformation of the composite. The extraordinary interface and structure strengthen the composite to a certain extent both at room and high temperatures.

Synergistic strengthening of aluminum with SiC by grain refinement and dispersion hardening

AbstractThis study investigates the synergistic effect of SiCp on grain refinement and dispersion hardening in Al matrix composites produced by ball milling followed by hot rolling. Al grains are effectively refined by generating significant dislocations and subsequent dynamic recrystallization during milling. The presence of SiCp stimulates the grain refinement process by more effectively reducing the grain size to ∼40 nm. Furthermore, an increase in the milling speed and duration reduces the grain size and improves the dispersion of SiCp, thereby enhancing the yield strength without any significant loss of ductility. Consequently, SiCp/Al composites exhibit a tensile strength of 430.27 MPa with more than 4% of elongation before failure, indicating a strength enhancement of ∼325% compared to the unmilled pure Al counterpart.

Towards the work hardening and strain delocalization achieved via in-situ intragranular reinforcement in Al-CuO composite

Dense intragranular distribution of nanoscale reinforcements is highly desirable since it is effective in reconciling the strength-ductility trade-off in Al matrix composites (AMCs). Herein, we report a systematic investigation on the work hardening and strain delocalization in Al-5 wt.% CuO (Al-5CuO) composite with strength-ductility synergy contributed by in-situ dense intragranular nanoscale Al2O3. Results reveal that Al-5CuO exhibits prominent hetero-deformation induced (HDI) strengthening as indicated by its larger HDI stress than effective stress. We showcase that the notable pile-ups of geometrically necessary dislocations (GNDs) at intragranular Al2O3 result in the prevailing kinematic hardening. While the plastic relaxation dislocations (PRDs) around Al2O3 generated by the release of GND-induced internal stress produce isotropic hardening. Both contribute to the pronounced work hardening of Al-5CuO. Comprehensive characterizations suggest the GND distribution with marked intragranular feature in Al-5CuO during straining, which implies the effective provoking of grain interior rather than grain boundary (GB)/interfacial zone to take plastic strain. On basis of the well-described storage and annihilation of GNDs and PRDs at the intragranular Al2O3, the microstructure-based strain-hardening model enables an in-depth understanding of the kinematic and isotropic hardening contributions by Al2O3 in Al-5CuO. Systematic analysis further confirms the important roles of intragranular Al2O3 in improving the strain partitioning, strain/stress transfer and strength matching across different domains of Al-5CuO, which significantly contributes to strain delocalization and hence strength-ductility synergy. This work sheds important insights on the innovative design of strong and ductile AMCs with intragranular nanoscale reinforcements for structural applications.

Nano-Phase and SiC-Si Spherical Microstructure in SiC/Al-50Si Composites Solidified under High Pressure.

The formation of coarse primary Si is the main scientific challenge faced in the preparation of high-Si Al matrix composites. The SiC/Al-50Si composites are prepared by high pressure solidification, which allows the primary Si to form a SiC-Si spherical microstructure with SiC, while the solubility of Si in Al is increased by high pressure to reduce the proportion of primary Si, thus enhancing the strength of the composites. The results show that the high melt viscosity under high pressure makes the SiC particles almost "fixed" in situ. The SEM analysis shows that the presence of SiC in the growth front of the primary Si will hinder its continued growth and eventually form SiC-Si spherical microstructure. Through aging treatment, a large number of dispersed nanoscale Si phases are precipitated in the α-Al supersaturated solid solution. The TEM analysis shows that a semi-coherent interface is formed between the α-Al matrix and the nanoscale Si precipitates. The three-point bending tests shows that the bending strength of the aged SiC/Al-50Si composites prepared at 3 GPa is 387.6 MPa, which is 18.6% higher than that of the unaged composites.

Microstructure and mechanical properties of CrMnFeCoNi high entropy alloy/Al composite with different reinforcement content

The Al matrix composites with different HEA addition ranging from 5.2 wt. % to 19.8 wt. % were fabricated by rotation friction extrusion (RFE) process. The microstructure results revealed that the average grain size of the composites was pronouncedly reduced by 70.5–81.8 % than that of the RFE processed aluminum (RFEed Al), and abundant second phases were formed in the composites. The ultimate tensile strength (UTS) increased with the HEA content. Significantly, the UTS of the composite with 19.8 wt. % HEA content was 224.5 MPa, increased by 150.8 % compared with the RFEed Al, and the good uniform elongation of 16.7 % was maintained. The improvement in mechanical properties was caused by the grain refinement mechanism, Orowan strengthening, load transfer strengthening, and dislocation strengthening. The strain hardening ability of the composites was higher than that of the RFEed Al and increased with the HEA content, as a result of the formed second phases and the added HEA particles. However, the strain hardening rate of the composites decreased quickly because of the high dynamic recovery rate caused by fine grains, resulting in the low uniform elongation of the composites. The current research provides a fundamental understanding to develop HEA/Al composites.

A novel way to fabricate high elastic modulus and high strength of TiC reinforced aluminum matrix composite

ABSTRACT This study presents an experimental investigation on Al matrix composites (AMCs) reinforced titanium carbide (TiC) nano-particles produced by five accumulative roll bonding cycles and three cryorolling (CR) cycles. The microstructures and mechanical properties of composites were studied. The results exhibited consequentially improved mechanical properties for processed Al/TiC AMCs as the number of rolling cycles increased. The presence of TiC in Al matrix showed the combination of elastic modulus, hardness, yield, and ultimate tensile stress of 84 ± 2GPa, 86 ± 3HV, 240 ± 12MPa, and 308 ± 15MPa, respectively. The dispersion of TiC particles was improved with increasing in the number of rolling cycles, resulting in a decrease in porosity between the matrix and reinforcement. This phenomenon was attributed to the breakup of particle clusters and their subsequent uniform dispersion within the Al matrix under CR. The composite microstructure shows uniform TiC particle distribution and grain refinement in the Al matrix, which all contribute to the enhanced mechanical properties.

Deformation behavior and mechanical properties of rolled carbon fiber reinforced Al-matrix composites via protection with Sn layer

How to break the restriction of elongation mismatch between the continuous carbon fibers and Al matrix in the rolling process has become a major obstacle for developing the rolled carbon fiber reinforced Al matrix (CF/Al) composites with high-performance. Herein, a strategy for liquid protection was proposed to overcome the damage of continuous CFs in rolling process of Al matrix by constructing the CF/Al composites with coating structure of Sn layer ([[email protected]]/Al composites). The design on the stress distribution and CFs damage in the rolling deformation of [[email protected]]/Al composites was optimized based on the numerical simulation. The micro-computed tomography (micro-CT) reconstruction indicated that the implantation of Sn can effectively release the stress concentration in CFs to prevent the CFs broken. After the heat treatment, the transition layer with eutectic Al-Sn structure (~550 nm) formed between the Al-matrix and CF-reinforcement, which can be used as weak boundaries, benefits to the load transfer to the CF-reinforcement with an with an increase of 23% in Vickers hardness. More importantly, the tensile strength of rolled [[email protected]]/Al composites can reach 256 MPa, which are 42.2% and 68.4% higher than that of rolled Al-matrix and rolled CF/Al composites (180 MPa and 152 MPa), respectively. This study could motivate the ingenious design of CFs damage protection for developing the advanced CF/Al composites in the automotive and aerospace industries.

Investigation of microstructure, mechanical, and tribological properties of SiC/h-BN/Gr hybrid reinforced Al6061 matrix composites produced by hot extrusion method

In this study, new generation hybrid composite materials were produced by adding SiC, h-BN and Graphite (Gr) to the Al6061 alloy, which has light, corrosion resistant, good formability and weldability properties, giving it abrasion resistance and high strength properties. Five different reinforced and non-reinforced samples were produced, namely Al6061, Al6061%10SiC, Al6061%8SiC%2 h-BN, Al6061%8SiC%2Gr, and Al6061%8SiC%1 h-BN%1Gr, by the hot extrusion method. The density, hardness, microstructure, tensile strength, transverse rupture strength (TRS), and abrasion properties of the synthesized samples are reported in this study. While small agglomerations were observed in the composite materials (10%SiC) produced with a single reinforcement element, it was almost absent in the hybrid composite materials. The hardness of the SiC- and h-BN-containing composites were higher than those of Al6061. The tensile strength and TRS improved relative to those of the reinforcement elements. The addition of h-BN and Gr improved the wear properties.

Application of grey-ANFIS system to optimize the drilling characteristics of nano SiC reinforced Al matrix composites

Application of grey-ANFIS system to optimize the drilling characteristics of nano SiC reinforced Al matrix composites

Improved properties of Al matrix composites reinforced with Ni-coated β-Si3N4 whiskers

ABSTRACT In order to enhance the interfacial bonding between aluminum and β-Si3N4 whiskers in Al matrix composites (AMCs), Ni coating was deposited on the surface of β-Si3N4 whiskers using an electroless plating method. The interfacial test results showed that Ni coating was successfully deposited on the surface of β-Si3N4 whiskers and the whiskers were well bonded with Al matrix without pores. In addition, the whiskers were homogeneously dispersed in the Al matrix. The effect of Ni-coated β-Si3N4 whiskers on the mechanical properties of composites was investigated in detail. Densification and the mechanical performance of AMCs reinforced by Ni coated β-Si3N4 whiskers (NSAMCs) were improved comparing to that of AMCs reinforced by uncoated β-Si3N4 whiskers (USAMCs). The maximum value of tensile strength and bending strength reached up to 290 MPa and 487 MPa, when the Ni content was 0.9 vol.% and the β-Si3N4 whiskers content was 20 wt.%, respectively. However, excessive Ni content weakened the strengthening effect. Medium Ni coating on β-Si3N4 whiskers significantly optimized the interface and improved the performance of the composites.

In Situ Formation of Al3Ti and Its Effects on the Microstructure, Hardness and Tribological Properties of Al Matrix Composites with Various Ti Contents

At present, Al matrix composites (AMCs) have drawn much attention owing to their light weight, high specific strength, high thermal conductivity, and superior excellent wear resistance, which endows them with great potential in the aerospace, automobile and military industries. In this study, AMCs with different Ti contents (0, 5 and 10 vol.%) were prepared by powder metallurgy. During the sintering, Al3Ti particles were in situ formed in the Al matrix. It was found that the Ti completely reacted with the Al matrix and formed fine in situ Al3Ti particles in Al-10Ti, while some large Ti-Al3Ti core-shell formed in Al-5Ti due to the incomplete reaction between the Ti and the Al matrix. Furthermore, the hardness of the composites was significantly improved by the in situ formed Al3Ti particles, reaching 143.3 HV in Al-5Ti and the highest value at 331.2 HV in Al-10Ti, respectively. The wear resistance of the composites is remarkably enhanced by Al3Ti particles compared to the unreinforced Al. Al-5Ti has the highest wear resistance among the samples. The wear resistance of the Al-10Ti composite becomes slightly deteriorated compared to Al-5Ti due to the brittle nature of Al3Ti, which leads to a three-body abrasive wear.

Synergistic effects of TiC/GNP strengthening on the mechanical and tribological properties of Al6061 matrix composites coupled with process optimization by artificial neural network

This study presents the strengthening of Al6061 alloy with titanium carbide (TiC) and graphene nano-platelets (GNPs), and the synergetic effect of these reinforcements on the microstructure, mechanical, and wear properties. The raw materials were combined in powder form in a hot press under a range of conditions (sintering temperature: 450 °C, 500 °C, or 550 °C, sintering time: 15, 30, or 45 minutes; and sintering pressure: 50, 100, or 150 MPa) to produce strengthened alloys containing 4, 8, or 12 wt.% TiC and 0.5, 1, or 1.5 wt.% GNP. A range of scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDS) showed that the reinforcement was uniformly distributed across the matrix. Raman spectroscopy showed that not there were no structural defects introduced into GNP during the mixing process of composite powders. Wear tests showed that minimum wear loss was obtained with an Al6061/TiC (8 wt.%)/GNP (1 wt.%) composite sintered at 500 °C and 100 MPa for 15 minutes. This same composite also displayed a decrease in the coefficient of friction (COF) of up to 69% when compared to unreinforced material. Examination of the areas of wear by SEM showed mixed type wear to be the dominant wear mechanism. Artificial neural network (ANN) was used to identify the impacts of different production parameters on wear loss. The trained ANN model was found to be highly accurate in predicting the wear properties of Al6061/TiC/GNP composites and could be used to generate an optimum set of production parameters to minimize wear loss without the need for costly and time-consuming experimentation.

Improving the ductility of Al matrix composites through bimodal structures: Precise manipulation and mechanical responses to coarse grain fraction

In this work, a powder metallurgy-thermomechanical method was proposed to fabricate bimodal composites with the forward design of coarse grain fractions. By optimizing chemical composition and sintering-extrusion parameters, precise manipulations of bimodal structures combining ultrafine and coarse grains have been realized. Bimodal structures lead to extra hardening and strain hardening, enhancing the ductility of ultrafine grained composites. Higher coarse grain fractions introduce more soft-hard domain interfaces in bimodal composites but decrease the strain hardening ability of domain interfaces. This work proposes a strategy to tailor the heterostructures quantitatively and deepens insight into the influences of coarse grain fraction on mechanical behaviors of bimodal composites.

Study of interfacial behavior on the damping characteristics of aluminum (Al)-Carbon nanotubes (CNTs) nanocomposites

In this work, MWCNTs-multi-walled carbon nanotubes of distinct reinforcement with Al matrix composite were fabricated by a novel route of dispersing Al-CNTs precursor, then integrated with compaction technique and sinter-forged process. The microstructural and dynamic behavior of as-produced Al-MWCNT composites were investigated, and the interfacial reaction was studied on the damping behavior of Al-CNT nanocomposite. Findings reveal a formation of aluminum carbide (Al4C3) formation at Al-CNT interface layers. A reaction arose at locations with an amorphous carbon coating at open ends of CNTs, in as-produced Al–CNT composites, carbon nanotubes with a wt. % of 0.75 has a solid interfacial interaction and obtained a damping capacity of 875 × 10−3 and a storage modulus of 82.9 GPa with a frequency of 1 Hz. This results in effective load transmission between the Al matrix and CNT, improving the dynamic behavior of the composite. However, the formation of the aluminum carbide phase contributes to the damping capacity of the aluminum reinforced with the wt. % of 0.75 and 1.0 CNT composite, which increases by 40 % and 21 % as compared to pure Al, whereas CNTs are identified as a capable coating for Al matrix to raise high absorb capacity at elevated temperatures subjected to the formation of Al4C3 phase without losing the mechanical behavior of the Al matrix.