Metal matrix composites (MMCs), especially aluminum matrix composites (AMCs), are widely used in the applications of aerospace, automotive, mechatronics and other areas due to the advantages of high specific strength, high specific modulus, and excellent thermal and electrical conductivity. In recent years, carbon nanomaterials as the reinforcement of MMCs, have attracted great attention for their outstanding mechanical and functional properties. This review focuses on the progress on preparation methods and mechanical properties of different dimensional carbon nanomaterials (0-D carbon nano-onions, 1-D carbon nanotubes, 2-D graphene et al.) reinforced AMCs. The design ideas of aluminum matrix composites with high strength and toughness through the structural construction have been summarized ranging from single- to multi-dimensional hybrid reinforcements, and the future research trends of MMCs have been prospected.

Interfacial structure plays a critical role in determining combination properties of the metal matrix composites (MMCs). In order to further increase the properties, it is important to modify interfacial structure through fabrication process. Owing to the excellent mechanical and functional properties of carbon materials, such as the diamond, carbon nanotubes and graphene, carbon reinforced MMCs has attracted much attention in recent years. This work reviewed various interfacial structure optimization methods and their influencing mechanisms on the mechanical and functional properties of carbon/metal matrix composites. Moreover, the future research interests related to carbon/metal interface studies are proposed.

Dimensional stability refers to the materials' ability to maintain their original size during long-term storage or under service conditions. The key components of the angle, velocity and position sensors, such as the gyroscopes, star sensors and optical observation devices, are extreme sensitive to the micro-deformation of the materials, and the dimensional instability of the present materials has become to be the bottleneck problem that restricts the accuracy of the equipment. Deep research has been carried out abroad from the aspect of the microstructure modification by heat-treatment and pretension deformation treatment of metals since 1970s. However, the domestic research on the dimensional stability is rather weak, which was mainly focused on the effect of the residual stress, and the corresponding engineering application effect is not pronounced. In the present work, the research experience and main results of the authors and coworkers on dimensional stability for decades have been introduced, including novel characterization method of dimensional stability during long-term storage (without stress), and the basic evolution process of the phase-stability, microstructure-stability and the anisotropy behavior of the Al alloys, which was revealed by the novel characterization method. Furthermore, the basic design principles of high dimensional stability and the design ideas based on the dispersivity of reinforcements of the Al matrix composites have been introduced. Moreover, the microstructure characters and the application effect in practical engineering of the high dimensional stability optical-grade and instrument-grade SiC/2024Al composites have been described. Based on the theoretical analysis and the practice effects, it indicates that the accuracy and accuracy stability of the instruments is mainly depended on dimensional stability of the used materials, and the dimensional stability of the materials was mainly affected by its intrinsic deformation characteristics, while the effect of the residual stress was subordinate. The present work also indicates that the application of the dimensional stability principle is also instructive to the technology upgrading of the high precision components, such as precision bearings.

Freestanding nanowires have ultrahigh elastic strain limits (4%~7%) and yield strengths, it is expected that composites reinforced by nanowires will have exceptional mechanical properties. However, the results obtained so far have been disappointing, primarily because the intrinsic mechanical properties of nanowires have not been successfully exploited in bulk composites. This is thought to be due to the inelastic strain incompatibilities at typical dislocation-piled-up interfaces. Therefore, we proposed a concept of elastic and transformation strain matching to realize the intrinsic mechanical properties of the nanowires. By creating a nanostructured composite consisting of nano Nb embedded in a NiTi matrix, the intrinsic mechanical properties of Nb nanowires, nano ribbons and nano particles are realized. Besides, this breakthrough triggers a new mechanism of stress coupling that induces the nanocomposite showing excellent mechanical properties. Based on the design strategy, we developed an in situ composite that possesses a large quasi-linear elastic strain of over 6%, a low Young's modulus of less than 28 GPa, and a high yield strength of 1.65 GPa.

This paper describes the research progress in hot deformation behaviors of discontinuously reinforced aluminum (DRA) composite, including research method, deformation mechanism and hot workability. The reliability of constitutive equation and processing map for description of flowing behaviors and deformation mechanisms in the previous studies were discussed. Based on that, the strain rate and temperature sensitivities of flow stress were introduced to further identify the deformation mechanisms. Deformation characteristics and microstructures of the composites with different reinforcements were illustrated. Finally, the future researches of hot deformation of DRA composite are suggested.

Carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) with ultra-high mechanical properties are attractive reinforcements to fabricate light weight, high strength metal matrix composites. In this paper, research progress on CNTs/GNPs reinforced magnesium matrix composites is systematically reviewed. This review focuses on the recent development of the preparation techniques, strengthening and toughening mechanism, interface structure of magnesium matrix composites reinforced by carbonaceous nanomaterials. Four kinds of preparation techniques are introduced, including powder metallurgy, stirring casting, disintegrated melt deposition and friction stir process. The yield strength of composites increases with the addition of GNPs/CNTs. Several possible factors can contribute to this: (1) grain size refinement; (2) load-transfer effects; (3) generation of the dislocation density due to strain generated by the thermal expansion mismatch between the matrix and GNPs/CNTs; (4) Orowan strengthening caused by the resistance of closely spaced GNPs/CNTs to the passing of dislocations. In addition, hydrogen storage behaviors, thermal properties and corrosion resistance of composites are also briefly introduced. In the end, this review summarizes the limitations of magnesium matrix composites at present stage as well as the prospect of its future development.

During the high-temperature melting process, Al is in full contact with SiC. The interface bonding properties of composites are closely related to the possibility and multi-directionality of interface reaction between them. A comprehensive understanding of the interfacial bonding, interfacial reaction, and interface structure between Al and SiC is of great significance for improving the material properties.There have been many researches on the wettability and interface reaction between Al or its alloys and SiC. However, there are still some differences and disputes on some issues, and the understanding of the true wettability of Al and SiC is not systematic enough. Reaction time and temperature have a great influence on the degree of interface reaction between Al and SiC, but there is still no systematic review on the specific relationship between reaction parameters and reaction degree. The addition of alloying elements can weaken the occurrence of interfacial reactions. However, under different reaction conditions, the relationship between the amount of alloying elements added and the reaction degree, and the mechanism of action of alloying elements on interface reaction have not been clearly reported. This article systematically reviews the interfacial reactions, interfacial products and reaction product evolution rules and mechanisms under specific reaction conditions, Al and the addition of different alloying elements to the SiC interface and interface wetting behavior. From the aspects of interfacial wetting, interfacial reaction and interfacial product, this article provided experimental data, theoretical references for the selection of process parameters during the preparation of composite.

Metal nanocomposites with delicate hierarchical structure (MNDHS), which provide excellent optical and catalytic properties due to their multicomponent and structural functionalization, are of great significance for the design of structural and functional materials as well as the application in the field of environment and energy. Here, butterfly wing template is used as an example to introduce the research progress of MNDHS, including their fabrication, property and potential applications, and then their development in the future is prospected.

The "material genetic engineering" plan, based on the large data, is to investigate the high throughput design, fabrication and characterization techniques with the aim to shift the material research from traditional mode to high throughput mode with low cost and fast response speed, and to accelerate the research and development of new materials and achieve the goal of "double reduction halves". As the metal matrix composites (MMCs) exhibit multi-components and a thermodynamically non-equilibrium state during fabrication, some key issues occur and need to be addressed including: (1) for high throughput fabrication, currently developed high throughput technologies based on thermodynamically equilibrium conditions, such as spray printing and multi-node diffusion methods, are not applicable for MMCs; (2) for high throughput characterization, there is a lack of multi- dimensional, field and scale acquisition technique for the composition, morphology, microstructure and property of MMCs. In order to solve these problems, the progress on the research and development of high throughput fabrication and characterization techniques of MMCs was reviewed, especially, in the field of gradient reinforced MMCs and their high throughput combination characterization methods, which may promote the application of high throughput fabrication and characterization techniques in MMCs. Finally, the bottlenecks and prospects in the high throughput fabrication and characterization of MM Cs are proposed.

Copper matrix composites have attracted a lot of interest regarding their application as electrical materials. However, the development of copper matrix composites has suffered setbacks because of a trade-off between electrical conductivity and strength. In this work, TiB₂ particles and TiB whiskers hybrid reinforced copper matrix composites were in situ fabricated by mechanical alloying and hot pressing. The microstructures of hot-pressed composites were characterized by XRD, OM, SEM and TEM. The mechanism of in situ reaction during hot pressing process and the influence of microstructures on physical properties of hot-pressed composites were analyzed. The Cu and Ti raw powders were firstly reacted at 800 ℃ by forming Cu₃Ti transient phase. Then, the Cu-Ti liquid micro-zone was formed at 850 ℃, which is higher than the melting point of Cu₃Ti phase. With the increasing of temperature further, TiB₂ particles and TiB whiskers were formed in the liquid micro-zone by the diffusion of B atoms from copper matrix. When the reinforcing phase is consisted of mainly TiB whiskers, the hardness of composites is relatively high. But the composites reinforced mainly by TiB₂ particles have a higher electrical conductivity. The combined properties of hybrid reinforced copper matrix composites were optimized due to the combination action of TiB₂ particles and TiB whisker. For the case of 3%(TiB₂-TiB)/Cu composites, the hardness and the electrical conductivity are 86.6 HB and 70.4% IACS, respectively.

TiB₂ strengthened Fe matrix composites (Fe-TiB₂) are potential lightweight materials for lightweight structure materials as they possess high modulus, low density, high strength and good ductility. More importantly, Fe-TiB₂ composite can be produced by eutectic solidification, which is suitable for massive production using thin slab casting and strip casting in the steel industry. The microstructure of Fe-TiB₂ composite is composed of ferrite matrix, primary TiB₂ and eutectic TiB₂ reinforcements. Ceramic TiB₂ is a hard brittle phase and it is easy to generate stress concentration when bearing load. The shape and size of TiB₂ can affect the mechanical properties of Fe-TiB₂ composite and the formability of sheet metal. The morphology and size of TiB₂ reinforcements are commonly observed using optical or electron microscope, which can only provide two-dimensional (2D) cross-section of the reinforcements. Nevertheless, the TiB₂ particles have various aspect ratios in three-dimensional (3D) space, which have not yet been well investigated. The present work proposes a new method combining deep etching and computer aided design (Creo Parametric) technology to reconstruct the 3D morphology of TiB₂ reinforcements in the Fe-TiB₂ composites. The OM, SEM were used to compare and analyze the 2D and 3D morphologies of the TiB₂ reinforcements. The fracture mechanism of the Fe-TiB₂ composite was reinterpreted by compression test. The results indicated that the primary TiB₂ reinforcements have an octahedral prism structure, which is mostly composed of two or even more single crystal prisms, and are randomly distributed in the matrix without preferred orientations. The eutectic TiB₂ reinforcements consist of lamelliform/fine columnar phase and dendrite phase. The lamelliform/fine columnar and dendrite eutectic phase in Fe-TiB₂ composite are more prone to brittle fracture than the primary phase TiB₂ during loading. Therefore, it is the main cause of fracture failure of the material during loading. The small TiB₂ particles observed by 2D microstructure do not exist in real 3D space. It is proposed that small and spherical TiB₂ particles are preferred and could be produced by controlling solidification process.

Mechanical vibration causes lots of damage in automotive industry, machinery manufacturing and aerospace field. Noise control also causes much damage to human health. So it is of great significance to seek materials with high damping capacity to alleviate or eliminate mechanical vibration and noise. Pure Mg has the highest damping capacity among all of the commercial metal materials, but its low mechanical property impose restrictions on its pervasive application. Therefore, magnesium matrix composites reinforced with high mechanical property reinforcement can exhibit excellent damping capacity and mechanical property simultaneously, and this kind of material has attracted great attention and interest from researchers in recent years. A variety of preparation methods has been utilized to prepare magnesium matrix composites reinforced with different reinforcements. In situ reactive infiltration is a relatively new processing method to prepare metal matrix composites, which combines the advantages of in situ reaction synthesis and pressureless infiltration, and it has received increasing attention because of its cost-effectiveness, simplicity and high-efficiency, and near-net shaping capability. And by tailoring the relative density of preform, magnesium matrix composites with a high volume fraction of ceramic reinforcement can be obtained. In view of the poor wettability of B₄C/Mg system leading to low efficiency of composite, Ti particulates with high melting point and immiscible with magnesium was added. And (B₄C+Ti)/Mg and (B₄C+Ti)/AZ91D composites have been prepared successfully by in situ reactive infiltration method with high efficiency and low cost. Microstructure, phase composition and damping capacities of the as-fabricated composites were characterized and analyzed. Results showed that with increasing the preparation temperatures, the reaction between the starting materials is more complete, and the microstructure of (B₄C+Ti)/AZ91D composites tends to be interpenetrating networks from particle reinforced structure. The strain-dependent and temperature-dependent damping capacities of (B₄C+Ti)/Mg and (B₄C+Ti)/AZ91D composites improve gradually with the increase of strain amplitude and temperature respectively, and the dominant damping mechanisms are dislocation damping and interface damping.

Al matrix composites (AMCs) have been used in the aerospace and automotive industries due to the desirable properties including high specific strength, superior wear resistance and low thermal expansion. However, the traditional fusion welding process of AMCs usually brings defects such as pores, particles segregation and detrimental phases, which limits the application of AMCs. So more and more attentions are paied on friction stir welding (FSW), a solid state welding method possessing great potential in the welding of AMCs. In this work, to acquire high quality and excellent fatigue property of friction stir welded SiC_p/6092Al composite joint, 3 mm-thick rolled SiC_p/6092Al composite plates with T6 state were conducted by FSW at a constant rotational rate of 1000 r/min, and at a low welding speed of 50 mm/min and a high welding speed of 800 mm/min, respectively. Microstructure evolution, mechanical properties and high cycle fatigue behavior of the FSW joints were evaluated. The results showed that high welding speed resulted in a much rougher surface of scale-like ripple and the morphology of the nugget zone was different from that of the joint at low welding speed. Significant enhancement of the hardness and tensile strength were achieved in the joints at the high welding speed, but the fatigue properties were not improved for the joints with unpolished surfaces. The fatigue limit of the joint at low welding speed was 150 MPa, however the fatigue limit reduced to 140 MPa at the high welding speed. For the joints with polished surfaces, obviously enhanced fatigue limit was achieved at the high welding speed of 800 mm/min compared to that of the joint at the low welding speed of 50 mm/min. Different fracture characteristics were observed in the specimens with unpolished surfaces at various cyclic stress loading. Under a low cyclic stress loading, crack initiated at the scale-like ripple on the surface of the specimen; under a high cyclic stress loading, crack also initiated at the scale-like ripple at the low welding speed, while the crack initiated at the swirl zone in the bottom of the nugget zone at the high welding speed. The results of three-dimension surface topography showed that a large surface roughness was achieved on the surface of the joint at the high welding speed, resulting in lower fatigue limit compared to that of the joint at the low welding speed. For the specimens with polished surfaces, the fatigue limit was improved by 40~65 MPa compared to that of the specimens with unpolished surfaces. In this case, a high fatigue limit of 205 MPa was obtained in the joint at the high welding speed of 800 mm/min, and all the specimens failed at the lowest hardness zone and nearby.

6xxx alloys have become of particular interest in automotive structural applications as replacements for low carbon steels, mainly because of the increasing demand for the utilization of lighter materials in the automotive industry. However, the strength and formability of the 6xxx alloy are inferior to those of fully annealed low carbon steels, which is partially due to the different crystallographic textures of these two materials. In-situ nanoparticle-reinforced composites have always been extensively used due to their high modulus, high strength, specific stiffness and excellent comprehensive properties. However, traditional in-situ methods require long reaction time and high reaction temperatures, leading to further growth or agglomeration of the reinforcement particles and decreasing the mechanical properties. In this work, in-situ ZrB₂/AA6111 composites were successfully prepared via an in-situ melt reaction with the assistance of an electromagnetic field. The effect of electromagnetic field on distribution, size and morphology of in-situ particles, interface structure between particles and matrix, and dislocation morphology in composites were characterized by XRD, OM, SEM and TEM. The action mechanism of electromagnetic field and the effect of microstructure on tensile strength were analyzed. The results indicated that with the assistance of electromagnetic field during in-situ reaction, the large particle clusters were broken into smaller clusters that were uniformly distributed in the matrix, the distribution of ZrB₂ nanoparticles was diffused and homogeneous with the size decreasing to 50~100 nm, and the corners of the nanoparticles clearly became obtuse. In addition, the interface between the particles and the matrix was well bonded without any impurities. The uniformity of the ZrB₂ nanoparticle distribution improved, resulting in dislocation propagation and entanglement. When electromagnetic frequency was 10 Hz, the optimal ultimate tensile strength (UTS), yield strength (YS) and elongation (El) of the composites prepared under the electromagnetic field were 362 MPa, 253 MPa and 25%, respectively, correspondingly increasing 38.7%, 68.6%and 28.7% over the respective properties of the ZrB_{2 np}/AA6111 composite. These improvements were due to the Orowan strengthening, load transmitting strengthening, grain refinement strengthening, and dislocation strengthening caused by the nano-sized ZrB₂ particles synthesized under the coupled electromagnetic and ultrasonic field. In addition, the Orowan strengthening contributed most to the improvement of properties.