Al Matrix Composites Research Articles

Influence of thermo-mechanical processing on microstructure and properties of bulk metallic glassy alloys-reinforced Al matrix composites prepared by powder metallurgy

Al-matrix composites, reinforced with two different types of glassy particles and prepared by mechanical alloying, were consolidated via Spark Plasma Sintering (SPS) and hot extrusion to produce high-strength Al–5%Al65Cu20Ti15 and Al–5%Al84Ni7Co3Nb6 composites, along with pure Al sample for comparison. TEM observation and XRD analysis were used to investigate the crystal structure of the prepared powders. Metallurgical analysis tools, including SEM, TEM, XRD and EBSD, were used to investigate the effect of consolidation temperature and processing on the amorphous phase and the distribution of reinforcing particles in the composite. Also, the effect of the consolidation process on the grain morphology and size of the prepared composite was studied. Al-5% Al65Cu20Ti15 was fully densified, compared to nearly 98 % relative density for Al-5% Al84Ni7Co3Nb6 and pure Al sample prepared by hot extrusion. Moreover, Al-5% Al65Cu20Ti15 composite showed the highest hardness and ultimate tensile strength values, which are 63Hv and 226 MPa, respectively. An acceptable elongation of 15 % was also achieved. After SPS, hot extrusion process improved the strength of the composite compared with previously reported Al composites containing higher percents of Al-based glassy articles manufactured using various processing techniques. Homogenous reinforcement distribution, grain refinement and improved wettability between matrix and reinforcement are the key factors on improving the strength of Al–5%Al65Cu20Ti15 composite. The coefficient of thermal expansion (CTE) decreased by adding glassy particles to the Al-matrix, while Al-5% Al65Cu20Ti15 had the lowest values.

Influence of Si, Ti, and Cu as alloying elements on the wettability and reactivity of an Al/B4C system

The wettability and reactivity of Al alloys and B4C are of vital importance in the production of B4C-reinforced Al-matrix composites. However, previous research has primarily focused on pure Al/B4C systems, with little focus on alloying elements. In this paper, we investigated the influence of Si, Ti and Cu as alloying elements on the wettability and interfacial reactivity of an Al/B4C system using improved sessile drop methods. The B4C substrate was not wetted by molten Al at 700−1000 °C, with initial contact angles higher than 100°. However, rapid spreading was observed in the initial stages due to the formation of Al3BC and Al4C3. Si had a noticeable effect on the interfacial wettability only at levels of 15 wt% or above, with the interfacial products changing from Al3BC and AlB2 to SiC-dominated phases. The addition of Ti to Al led to the formation of TiB2-dominated interfacial products, which replaced the Al3BC and AlB2 phases, with the spreading kinetics mainly controlled by interfacial reactions in the early stages and the diffusion of Ti from the bulk of the drop to the triple line in the later stages. The addition of Cu had a negligible effect on the wettability but slightly weakened the formation of AlB2 by promoting substrate dissolution.

Plain interface strategy toward the high corrosion performance of Al matrix composites

Plain interface strategy toward the high corrosion performance of Al matrix composites

Tribological behavior of Al matrix composites reinforced by hybrid Cu and SiC under SN500 + G lubricant

Al matrix composites reinforced with hybrid SiC and Cu reinforcement were prepared by powder metallurgy and sintering. The presence of Cu in the composite microstructure has caused the formation of a three-dimensional network of metallic reinforcing phase. Wear tests were performed (50 and 100 N, 1 mm/s, 1000 m) as dry wear and lubricated wear under SN500 base oil containing graphite particles. The friction results showed that the COF under lubricant compared to the dry wear test was decreased by ∼80 %. With increasing SiC/Cu content the wear rate was decreased up to 30 %. The SEM observation of the lubricated worn surfaces showed that adhesive wear was the dominant wear mechanism, which significantly decreased with the tribofilm formation.

Constitutive equation and microstructural evolution of one distinctive Al–based hybrid composite reinforced by nano–AlN and micro–TiC particles during hot compression

In this study, an (8.2AlN + 4TiC)/Al–0.3Fe–0.1Mn composite was successfully fabricated for elevated– temperature applications by the liquid–solid reaction method, and the high–temperature performance (hot workability) of the composite was evaluated by unidirectional hot deformation experimentation. The tested temperatures and strain rates were 350–500 °C and 0.001–1 s−1, respectively. The results indicated that the peak stress of the composite was as high as 226 MPa at 350 °C and 1.0 s−1, which was significantly higher than the reported strength values of commercial deformed aluminum alloys or other particle–reinforced Al matrix composites under the same experimental conditions. Although the flow stress of the composite decreased with the increase of deformation temperature and the decrease of strain rate, the peak stress remained at 82 MPa under the experimental conditions of 500 °C and 0.001 s−1. This reflected the excellent high–temperature synergistic strengthening effect of the in–situ nanosized AlN and submicron TiC particles. Based on the true stress–true strain curve, the hot deformation constitutive equation of the composite was established and fitted. The relative microstructural evolution of the composite during hot deformation was characterized by electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM). It was found that the Orowan strengthening and load–transfer strengthening effect of the nanosized AlN and submicron TiC particles were the main reasons for their high–temperature strengthening, and the softening effect of the composite could be attributed to dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX), accompanied by partial discontinuous dynamic recrystallization (DDRX). This study provided a new strategy for the design of heat–resistant Al alloys and their high–temperature strengthening and softening mechanism. This study may provide new insights for designing and achieving good workability in Al–based composites for elevated temperature applications.

CNT-induced heterogeneous matrix grain structure in CNTs/Al composites

Ductility collapse is a stubborn issue for developing high-strength Al matrix composites reinforced with carbon nanotubes (CNTs). In order to solve this problem, here we manipulated the fabrication process and crafted a heterostructured CNTs/Al composite consisting of fine-grained zone (FGZ) and quasi-continuously networked coarse-grained zone (CGZ). Such heterostructured CNTs/Al composite with CGZ in a quasi-continuously networked fashion has never been reported before. Microstructural analysis showed that the majority of CNTs resides in FGZ, which stimulated dynamic recrystallization of Al during hot deformation and resulted in the formation of FGZ. Tensile tests showed that the heterostructured composite possesses a tensile property of 549 MPa of strength and 11.2% of ductility, which is superior to those in literatures. Further in-situ tensile EBSD and post-tensile TEM analyses revealed that during tensile deformation, the stiff FGZ undertook most of the stress, whereas the CGZ facilitated hetero-deformation induced hardening, which helped to resist the high flow stress of FGZ and assisted the ductility retention. This study may provide some guidance for the development of strong yet ductile CNTs/Al composites.

Gaining strength-ductility combination in Al matrix composites with in-situ synthesized three-dimensional nanocarbon network

As a promising architecture reinforcement, the three-dimensional (3D) configuration of nanocarbon holds great prospects in achieving a strength-ductility combination for metal matrix composite (MMCs). However, due to the native deficiency of Al in catalyzing the growth of nanocarbon, constructing a nanocarbon network has been the long-term challenge for Al matrix composites (AMCs). Herein, we develop a new strategy for synthesizing AMCs reinforced by three-dimensional nanocarbon (3D-C) via plasma-enhanced chemical vapor deposition (PECVD) integrated with hot pressing (HP) as well as hot extrusion, demonstrating exceptional mechanical properties. The detailed characterization reveals that the in-situ generation of nanocarbon layers on the surface of Al powders is attributed to the initiation of isolated carbon islands, followed by merging and self-assembly, which is governed by the PECVD-assisted catalysis growth-regime. The subsequent welding of nanocarbon layers during the HP promotes the formation of interlocking 3D-C networks in Al matrix, enhancing the sintered densification of the composite. Such unique nanocarbon distribution configuration not only effectively constrains the coarsening and deformation of Al grains, but also notably accumulates dislocation under high stress conditions. Moreover, 3D-C with a strong interfacial bonding contributes to the toughness through the microcracks, bridging cracks as well deflecting cracks, which accounts for the high toughness of the composite. This work provides new insights into the 3D distribution configuration of reinforcements in AMCs to achieve the optimized mechanical performance of composites.

Revealing the Interface Characteristic and Bonding Ability of CoCrFeNi High Entropy Alloy/Al Composite by First-Principles Calculations.

In this work, the interfacial atomic bonding process and atom-matching structure of Al atoms deposited on the crystal plane of CoCrFeNi HEA were investigated by first-principles calculations. The relevant physical parameters, including crystal structure, lattice constants, chemical bonding, and differential charge distribution, were studied in detail. The results showed that the constructed crystal model of CoCrFeNi HEA has a stable structure, and the binding energy of Al atoms deposited constantly on different crystal planes at different sites is less than -16.21 eV, indicating a strong interface bonding ability. With the increase in deposited atoms, the material is subjected to a phase transition from two-dimensional chemical adsorption of Al atoms in a single layer to three-dimensional chemical binding of the bulk. Furthermore, the electron cloud occurred through the interaction of positive and negative charges at the interface, indicating that the charge has been transferred along with a chemical bond between Al and CoCrFeNi atoms. It can be thought that the interface formed a stable structure and possessed low mismatch stress. This work provides a theoretical basis for designing CoCrFeNi series HEA-reinforced Al matrix composites.

Tailoring the enhanced mechanical behavior of 6061Al composites via nano SiCp and micron B4Cp addition

In this work, the hybrid micron B4C particles (m-B4Cp) and nano SiC particles (n-SiCp) reinforced 6061Al matrix composites were prepared by powder metallurgy. The synergistic effects of hybrid m-B4Cp and n-SiCp were investigated. The results showed that m-B4Cp were well dispersed in the matrix, while n-SiCp were uniformly distributed inside the grains as well as at the grain boundaries. The coupled addition of n-SiCp and m-B4Cp significantly refined the grain size of matrix from 3.60 μm to 0.91 μm. The synchrotron X-ray computed tomography (SR-CT) revealed that the volume of pores increased with increase of particle content. Compared with the composites reinforced with only one type of particle, the 6061Al composites reinforced with micro and nano dual-size particles possessed higher tensile strength, while maintaining reasonable plasticity. The strengthening contributions to the yield strength improvement of 6010Al matrix composites reinforced with micro and nano dual-size particles are resulted from thermal expansion mismatch strengthening, fine grain strengthening and Orowan strengthening caused by n-SiCp.

Large scale production of graphene aluminum composites by stir casting: Process, microstructure and properties

Graphene has recently garnered significant attention as an exceptional nanofiller for aluminum (Al) matrix composites due to its remarkable mechanical strength, elevated thermal and electrical conductivities. For practical industrial applications, it is necessary to develop large-scale production technology. To this end, we have utilized a scalable stir-casting process to fabricate graphene-reinforced aluminum matrix composites. The microstructure, mechanical properties, electrical and thermal conductivities of the composites with varying graphene contents were characterized. Through testing, it was confirmed that graphene remained intact within the aluminum matrix during the stir-casting process, and the damage to the graphene sheet during the fabrication of composites was slight. High-resolution microscopic observation shows that aluminum, graphene and aluminum carbide co-exist within the composites. Compared to its pure aluminum counterpart, the Vickers hardness of the optimal composite sample (with a graphene content of 0.2 wt.%) exhibits a significant increase of 42%. Also, this superior composite sample exhibits a remarkable increase of 5% and 38% in its electrical and thermal conductivities respectively. The performance evolution and improvement mechanisms have been thoroughly investigated and revealed. The test results suggest that preformed blocks and stir casting are promising technologies for the large-scale production of graphene-aluminum composites.

Influence of Heat Treatment on the Mechanical Properties and Precipitation Kinetic of Sugar Palm Fiber Ash Reinforced LM26 Al Matrix Composites

Heat treatment is a commonly known treatment subjected to aluminum alloy and their composites to improve their mechanical properties for automotive, aerospace, and marine applications. The heat treatment was carried out to determine the influence of aging time and temperature on the mechanical properties of LM26 Al alloy reinforced with 0, 2, 4, 6, 8, and 10 wt% sugar palm fiber ash (SPFA) and its precipitation kinetics. The LM26 Al/SPFA composites were fabricated through the stir casting technique, solutionized at 500oC for 2 h, and quenched in water at room temperature. The quenched composites were aged at various ageing times and temperatures and allowed to air cool. The hardness, impact energy, tensile, and compression strengths of the aged composites were appraised. In addition, the precipitation kinetics were studied to validate the precipitation temperatures of LM26 Al matrix composites. The hardness of the composites increased with aging time and temperature, with LM26 Al/10 wt% SPFA composite reaching a hardness peak of 102.10 VH at an aging temperature of 180oC after 5 h, compared to 56.70 VH for LM26 Al alloy. Similarly, after 5 h of aging at 180oC, the LM26 Al/8 wt% SPFA composite achieved maximum tensile and compression strengths of 198.21 MPa and 326.22 MPa, respectively. Precipitation temperature decreased from 584.8oC (LM26 Al alloy) to 480.46oC (LM26/ 10wt% SPFA), indicating that adding SPFA improved precipitation kinetics. The age-hardened composite with high hardness, tensile strength, and compression strength makes it a promising piston material application in the automotive industry.

Mechanical response and microstructure evolution of SiC particle-reinforced Al-MMCs under ultrasonic loading

High volume fraction(≥45 vol.%) SiC particle-reinforced Al matrix composites are difficult for forming and manufacture. A simple and efficient method is proposed in this research to realize rapid plastic deformation at room temperature. By applying ultrasonic load to the composites, 40% compressive strain is obtained within 1s, while the stress is only 59MPa, about 1/10 of its compressive strength. Ultrasonic loading can produce a high instantaneous strain rate (up to 103 s-1) and a high-frequency (20000Hz) cyclic load compared with conventional loading. The stress superposition and relief effects produced by ultrasonic loading lead to the diffusion and annihilation of dislocation in the Al matrix, the dispersion, and the plastic deformation of SiC particles. The microstructure evolution reduces the accumulation of dislocation, promotes the formation of sub-grain, weakens the deformation texture, and improves the synergetic deformation of Al and SiC.

Achieving high strength and ductility in high-entropy alloy particle reinforced Al matrix composites with proper proportion of layered structures

Particle spatial distribution has a significant influence on mechanical behavior of particulate reinforced Al matrix composites fabricated by powder metallurgy, which has been systematically investigated in our work. The results showed that, by regulating the milling time for 1 h, 10 h and ≥ 20 h, assisted by hot pressing and hot extrusion processes, three typical distributions of high-entropy alloy (HEA) particles within the Al matrix composites were constructed, i.e., particle agglomerated composite, uniformly distributed composite, and layered structure composite, respectively. After a long-time high energy milling, alloying behavior did not occur between the Al and HEA particles. Moreover, the composite with a proper proportion (19 vol%) of layered structures achieved good combination of yield strength (445.2 MPa) and fracture strain (5.4%), which was ascribed to the strengthening and toughening effect induced by bimodal gain structure. The effect of layered structure on the composite was reflected in two points: first, due to the differences in dislocation density and consumption degree of Cu atoms, the size and density of precipitates in the large particle zones differ from those in the layered structured zones. Second, according to the finite element analysis, though high content of layered structures brought high strength in the composites, it also caused stress concentration, which could reduce the ductility of composites. The dominant strengthening contribution of the layered structure in the composites was derived from the grain boundary strengthening. This research provides a new insight into Al matrix composites with different reinforcing particle distribution.

Preparation and characterization of Al-Mg-Si matrix composites reinforced with Ti2(Al,Si)C solid solution

The Ti2(Al,Si)C/Al-Mg-Si composite was fabricated by in-situ solid solution of Si to Ti2AlC during spark plasma sintering. The composition of Al-Mg-Si matrix alloy was effectively regulated by the addition of Si. The elemental distribution and atomic composition in Ti2(Al,Si)C particles and Al-Mg-Si alloy, as well as the microstructure of precipitated Mg2Si phase were carefully investigated. The composite after T6 heat treatment exhibits the ultimate strength of 428 MPa, yield strength of 358 MPa, and fracture strain of 4%. This research provides a novel method to balance the strength and plasticity of Al matrix composites.

Deformation mechanisms in the cutting process of SiCp/Al composites using the molecular dynamics (MD) approach

In order to clarify the reasons for the emergence of problems such as high machining difficulty and poor machining surface quality encountered in the machining process of SiCp/Al composites, this paper presents a simulation study of the deformation mechanism occurring during the cutting process of SiCp/Al (SiC particle-reinforced Al matrix composites) by using the molecular dynamics (MD) method. The mechanism of strengthening and hardening occurring during cutting of SiCp/Al composites is discussed in terms of the slip expansion of dislocations and the interaction between different types of dislocations. It is found that the presence of SiC balls hinders the slip and expansion of dislocations in the Al (aluminum) matrix, resulting in the strengthening of the Al matrix between the SiC (silicon carbide) balls, mainly because the dislocations in the workpiece interact with each other during the cutting process to form dislocation tangles, stacking layer dislocations and dislocation locks, which hinder the slip and expansion of dislocations and thus increase the strength of the Al matrix. By analyzing the stress distribution inside the workpiece during the cutting process, it is found that the stress inside the workpiece is mainly concentrated in the area where the tool flank face is in contact with the workpiece, which is the main reason for the occurrence of working hardening in SiCp/Al composites.

Mechanistic understanding of strengthening in a novel MXene/AlSi10Mg matrix composite processed by laser powder bed fusion

The fabrication of high-performance two-dimensional nanosheets strengthened Al matrix composites (AMCs) is challenging due to the agglomeration issue of traditional nanosheets (graphene) and their high reactivity with Al powder. To address these concerns, Ti3C2 MXene nanosheets with superior chemical stability were employed as a substitute for graphene in this study. Furthermore, a novel MXene/AlSi10Mg composite powder for the laser powder bed fusion (LPBF) was synthesized using a powder coating strategy. The approach involves three steps, including intercalation treatment of MXene flakes, uniform dispersion of the delaminated MXene nanosheets in aqueous solution, followed by the powder coating treatment using a solid-liquid fluidized bed. Differing from conventional methods for making powder mixtures, such as mechanical blending and ball milling, our powder coating approach achieved uniform distribution and high purity of MXene on the surface of AlSi10Mg powder, while maintaining the original sphericity and flowability of powder. The MXene-coating exhibited exceptional stability under intense conditions of high-energy laser exposure and high-temperature Al melt, enabling the successful retention of MXene nanosheets after LPBF processing. Experimental results show that the retained MXene effectively strengthened the Al matrix through load transfer from Al matrix, pinning effect on the movement of grain boundaries, and inhibiting effect on the deformation and fracture of eutectic Si. Consequently, compared to the bare AlSi10Mg sample processed by LPBF, a small addition of MXene (0.25 wt%) yielded a significant improvement in tensile strength (over 60%), while maintaining an acceptable ductility.

Mechanical properties and fracture behavior of Al(111)/MgAlB4(0001) interface in Al matrix composites: a first-principle calculation study

Hexagonal crystal MgAlB4 is a strengthening phase in Al matrix composites, which can significantly improve ultimate tensile strength. In this paper, the surface perform, interfacial bonding characteristic, fracture mechanism, and electronic properties of the Al(111)/MgAlB4(0001) interface were thoroughly investigated by the first principles method. The results reveal that the top-site and bridge-site configurations were more unstable than the hollow-site. Besides, from the calculated results of interfacial energy and work of adhesion, the hollow-stacked Al(111)/B(Al)-terminated/MgAlB4(0001) interface expresses stronger stability than other interfacial models, which is attributable to the higher work of adhesion and lower interfacial energy of the hollow-stacked Al(111)/B(Al)-terminated/MgAlB4(0001) interface. Analysis of electronic structure reveals that the Al-termination and Mg-termination Al(111)/MgAlB4(0001) interface presents Al-Al and Al-Mg metallic bonds at the interface, respectively, but the B(Al)-termination Al(111)/MgAlB4(0001) interface expresses strong Al-B covalent bonds characteristic, which leads to the highest interface stability. The results of tensile fracture revealed that the HCP stacked B(Al)-termination interface transferred the external stress to Al bulk, due to the Al-B covalent bond formed near the interface. Therefore, ceramic phase MgAlB4 can effectively promote the particle reinforcement of Al matrix composites.

Microstructure evolution, interface and mechanical properties of SiCp/2A14 joint during laser keyhole welding

Welding problems have restricted the applications of lightweight SiCp/Al composites in aerospace. In this work, the controllability of the keyhole mode, nucleation mechanism, and mechanical properties of the laser-welding process are studied in detail. The extrusion effect formed by the open keyhole pushes SiC particles to the bottom of the molten pool. To observe the nucleation and growth mechanism of the Al4C3 of keyhole laser-welded SiC/2A14Al composites, the dissolution–precipitation behavior of the SiC particles and growth behavior of the Al4C3 tip were observed. Owing to its high chemical properties, Al4C3 mainly begins nucleating from the open edges of the SiC particles and its formation is mainly distributed along the direction of Al grains. Al4C3 was the main crack source and propagation path while the small-sized SiC particles hindered the crack propagation. This work innovatively regulates the keyhole mode to achieve ‘small damage breakdown’ laser welding, greatly reducing the volume fraction of Al4C3. It also provides new insight into fusion welding of SiC particle-reinforced Al matrix composites.

Electromagnetic Preparation and Wear Behavior of In Situ Si‐Reinforced Al–Matrix Gradient Self‐Lubricating Composites

In this work, a novel Sn self‐lubricating Al–matrix composites with in situ Si‐reinforced gradient structure ([Sn×Si‐rich]⊚Al–matrix composites) is proposed. [Sn×Si‐rich]⊚Al–matrix composites is successfully prepared by controlling synergistic separation of primary Si and Sn under rotating magnetic field. In the results, it is shown that the wear‐resistant structure of “soft Sn surrounding hard Si” persists in [Sn5×Si‐rich] layer. [Sn5×Si‐rich]⊚Al–matrix composites with 5 wt% Sn addition is advised to balance self‐lubrication of Sn with its negative effects on hardness and tensile strength. The Vickers hardness of [Sn×Si‐rich] Al–matrix for [Sn5×Si‐rich]⊚Al–matrix composites reaches 1062 HV/120 HV, successfully achieving gradient design of mechanical properties. Meanwhile, tensile strength and average coefficient of friction (COF) value/wear rate are 263 MPa and 0.43/3.81 × 10−4 mm3 (N·m)−1, respectively. Furthermore, the average COF and wear rate of [Sn5×Si‐rich]⊚Al–matrix composites increase first, then decrease slightly, and finally increase, with increasing wear temperatures. And the lower COF/wear rate of 0.52/5.41 × 10−4 mm3 (N·m)−1 occurs at 300 °C as a turning point, because the soft Sn melts into liquid phase and can better spread over wear surface to form a self‐lubricating film to reduce wear. This study can accelerate the development and application of Sn self‐lubricating Al–matrix composites in high‐temperature industrial systems for automotive lightweight and aerospace.

Comparison of microstructural, texture and mechanical properties of SiC and Zn particle reinforced FSW 6061-T6 aluminium alloy

This work investigates the microstructure, mechanical characteristics, and texture evolution of friction stir welding (FSW) of AA6061-T6 metal matrix composites (MMCs) reinforced with silicon carbide (SiC) and zinc (Zn) particles. The SZ region of the SiC and Zn particle-reinforced aluminium matrix (Al-matrix) composites has ultra-fine grain refinements of 4.79 and 4.18 μm, respectively, compared to base metal (BM) particle sizes of 44.97 μm. Ultra-fine grain refinement in the SZ zone produces dynamic recrystallization with particulate-driven nucleation, Zenner Hollomon, and homogeneous SiC/Zn particle distribution in the Al-matrix. Recrystallization texture components P {011} <112>, cube {001} <101>, rotating cube (H) {001} <110>, and F {111} <112>, along with primary shear texture components (B/B¯, and C), suggested DRX at the joint interface in the SiC-reinforced Al-matrix composite. However, the Zn-reinforced Al-matrix composite has a high plain strain, recrystallization, and deformation texture components of copper {112} <111>, Brass {011} <211>, cube {001} <101>, Goss {110}, and P 011 <112>, and major shear texture components (B/B¯ and C). SiC and Zn-reinforced Al-matrix composites have 110 ± 4 and 120 ± 5 HV0.2 average microhardness, respectively. Also, SiC and Zn-reinforced Al-matrix composites have 224 and 236 MPa tensile strengths, respectively.