Current Status of Preparation, Processing, and Application of Aluminum Matrix Composites [[SMM Aluminum Conference]]

On April 18, at the AICE 2025 SMM (20th) Aluminum Industry Conference & Aluminum Industry Expo - Industrial Aluminum Extrusion Forum, hosted by SMM Information & Technology Co., Ltd. (SMM), SMM Metal Trading Center, and Shandong Aisi Information Technology Co., Ltd., and co-organized by Zhongyifeng Jinyi (Suzhou) Technology Co., Ltd. and Lezhi County Qianrun Investment Promotion Service Co., Ltd., Professor and Doctoral Supervisor GENG Lin from the School of Materials Science and Engineering at Harbin Institute of Technology shared the current status of preparation, processing, and application of aluminum matrix composites.

Research Background of Aluminum Matrix Composites

National Significant Demand for Metal Matrix Composites

Aerospace: Large aircraft, heavy helicopters, unmanned aerial vehicles, carrier-based aircraft, hypersonic vehicles, near-space vehicles, and strategic transport aircraft.

Space: Heavy-lift launch vehicles, manned lunar missions, lunar bases, Mars sampling, small celestial body exploration, Jupiter system exploration, and satellites.

Other Fields: Robotics, rail transit, new energy vehicles (NEVs), deep-sea/deep-earth/polar exploration equipment, 3C electronics, etc.

Metal matrix composites have taken the first step towards large-scale engineering applications in China's aerospace, defense, electronics, construction machinery, and other fields, becoming one of the irreplaceable basic raw materials for major national projects.

He introduced the development history of aluminum matrix composites and pointed out that China ranks among the top internationally in terms of the total number of papers and the number of highly cited papers on aluminum matrix composites.

►Current Status of R&D on Aluminum Matrix Composites in China: Mainly concentrated in high-end manufacturing fields such as aerospace and defense.

Aluminum matrix composites have achieved widespread application in high-end manufacturing fields such as aerospace and defense, meeting the demands for small-batch, multi-variety, and customized production.

►One of the Bottleneck Issues in Widespread Application: The strong-toughness inversion problem, where stiffness and strength increase while plasticity decreases.

Nature-inspired configuration-based composite strengthening and toughening design has become the main trend in the development of aluminum matrix composites in recent years.

In terms of preparation technology, the influencing factors of composite systems are complex: High-quality preparation technologies that match different composite systems need to be selected to meet the demands of complex multi-field coupling applications.

In terms of forming and processing technology, the mechanism of microstructure evolution during the forming process is complex: Suitable forming and processing technologies need to be developed to meet the demands for precise shape and property control of complex thin-walled components.

Preparation Technology of Aluminum Matrix Composites

The preparation of discontinuously reinforced aluminum matrix composites involves various complex processes. Developing suitable preparation technologies is the key to obtaining high-performance composites.

II. Preparation Technology of Aluminum Matrix Composites - Solid Phase Method (Powder Metallurgy)

The solid phase method refers to the process of preparing metal matrix composites with the matrix in a solid state.

Advantages: Lower preparation temperature, easily controlled interfacial reactions, fine microstructure, and high composite performance.

It provides analyses of relevant cases, including aluminum matrix composites reinforced with uniformly configured ceramic particles based on traditional ball milling processes, CNT/Al composites with a brick-and-mortar configuration based on flake powder metallurgy, multimodal aluminum matrix composites based on multi-step ball milling, and aluminum matrix composites reinforced with phase change materials.

II. Preparation Technology of Aluminum Matrix Composites - Solid Phase Method (Hot Isostatic Pressing)

The hot isostatic pressing process involves placing the product in a sealed container, applying isotropic pressure to the product while simultaneously applying high temperature. Under the combined effects of high temperature and pressure, the product undergoes sintering and densification.

Most production-scale hot isostatic presses have a maximum operating temperature of approximately 1400°C, with maximum pressures ranging from 100 to 200 MPa. The total tonnage of the largest modern hot isostatic press is approximately 400,000 kN (40,000 tons-force).

Example: During the hot isostatic pressing preparation of high volume fraction SiCp/Al composites, the matrix aluminum alloy exists in a solid-liquid two-phase region, facilitating easier densification of the composite under high temperature and pressure conditions.

II. Preparation Technology of Aluminum Matrix Composites - Liquid Phase Method (Squeeze Casting)

Preform Preparation: Preparing uniformly porous preforms through physical sedimentation; preparing biomimetic configured preforms using methods such as freeze casting and 3D printing.

Composite Preparation: Infiltrating molten aluminum into the pores of the preform through mechanical pressurization to achieve the preparation of high-performance composites.

It discusses relevant cases, including aluminum matrix composites reinforced with uniformly configured particles, aluminum matrix composites reinforced with uniformly configured whiskers, and biomimetic configured aluminum matrix composites.

II. Preparation Technology of Aluminum Matrix Composites - Liquid Phase Method (Vacuum Pressure Infiltration)

Vacuum pressure infiltration is similar to squeeze casting, primarily involving the preparation of ceramic porous preforms first, followed by the combination of a vacuum environment and gas pressure pressurization conditions to enable the aluminum alloy melt to fill the micropores of the preform and solidify, thereby preparing aluminum matrix composites.

It introduces relevant cases of low-expansion, high-volume fraction particle-reinforced aluminum matrix composites and biomimetic configured aluminum matrix composites.

II. Preparation Technology of Aluminum Matrix Composites - Liquid Phase Method (Stir Casting)

Basic Principle: Directly adding particles into the semi-solid melt of the matrix metal to increase the shear stress during stirring, enabling uniform dispersion of the particles in the metal melt. Subsequently, rapidly heating to the liquid state to improve the casting liquidity, and finally casting into ingots, castings, etc.

Key technologies: Improvement of wettability between the melt and the reinforcement phase, uniform dispersion of the reinforcement phase, and control of oxidation and gas absorption in the metal melt.

Technological advantages: Suitable for industrial-scale production; simple process and low manufacturing costs.

Preparation capacity: The production scale of stir casting typically ranges from a few kilograms in the laboratory to several dozen tons in industrial production.

It elaborates on cases such as the stir casting preparation technology for SiC particle-reinforced aluminum matrix composites, graphite particle-reinforced aluminum matrix composites, and in-situ TiB₂-reinforced aluminum matrix composites.

The fluoride salt method mainly involves the reaction of two salts, generating fluoride salt by-products; the master alloy method produces no by-products but has high requirements for raw materials; the in-situ reaction-generated TiB₂ particle composite casting ingot can currently reach a maximum of 11t, providing ingots for subsequent plastic processing to prepare large components.

TiB₂ particles exhibit a network-like distribution. Their size can be controlled within the nanometer to submicron range, with regular particle shapes and no significant agglomeration; the in-situ reaction-generated TiB₂ particles have a good interface bonding with the aluminum matrix and are in a coherent relationship, making them ideal reinforcing ceramic particles.

TiB₂ particles are excellent grain refiners. In the molten metal, TiB₂ particles act as the core for heterogeneous nucleation, providing more nucleation sites during metal crystallization, ultimately resulting in finer and more uniform grains; a large number of dislocation tangles exist near TiB₂ particles as the second phase particles, effectively hindering dislocation movement during deformation, thereby enhancing the material's strength.

Compared to the matrix alloy, the HCF ultimate strength of TiB₂ particle-reinforced aluminum matrix composites is increased by 22% to 44%, reaching up to 730MPa; fine TiB₂ particles can inhibit fatigue crack initiation, avoiding the tendency for premature fatigue crack initiation due to particle-interface debonding and particle fracture.

Preparation Technology of Aluminum Matrix Composites - Additive Manufacturing Method

Based on additive manufacturing technology, it enables the net-shape forming of complex structural metal components with integrated material-structure, providing a new technological approach for the design and manufacture of high-performance components in aerospace, mainly divided into laser additive manufacturing, arc additive manufacturing, friction stir manufacturing, etc.

Preparation Technology of Aluminum Matrix Composites - Additive Manufacturing Method (Laser Additive)

Under the action of a laser beam, metal powder is melted and rapidly solidified to form a new layer of material. This process is carried out layer by layer until a complete three-dimensional object is constructed; based on the specified reinforcement particles and Al matrix that have been added, induced grain refinement can be achieved.The lower interatomic mismatch between the α-Al matrix and TiB₂ leads to a decrease in the critical nucleation undercooling ΔT, which can repair crack formation in alloys prone to cracking during the L-PBF process.

The addition of second-phase hard particles can significantly refine the microstructure, resulting in higher yield strength due to grain boundary strengthening, as verified in TiB₂-reinforced AlSi10Mg alloys and TiC/TiH₂-reinforced Al2024 alloys. In addition to grain boundary strengthening, the yield strength of the L-PBF TiB₂/AlSi10Mg alloy is increased to approximately 362-407 MPa due to the enhanced resistance to dislocation motion caused by the hard particles.

II. Fabrication Technologies for Aluminum Matrix Composites - Additive Manufacturing (Friction Stir)

Friction stir additive manufacturing (FSAM) involves local plastic deformation of metal materials using a high-speed rotating stirring tool, followed by layer-by-layer accumulation under pressure to achieve the fabrication of highly dense metal structures. The advantages of FSAM include low-temperature processing, energy conservation and environmental protection, applicability to difficult-to-weld materials, and low residual stress. It is mainly used for the compounding of dissimilar materials and the repair of high-value components, suitable for the efficient large-scale forming of materials such as aluminum alloys and magnesium alloys.

The NiTip/Al interface prepared by friction stir additive manufacturing exhibits good bonding without the formation of harmful reaction products. The addition of NiTip forms a fine-grained microstructure with good dispersion, accelerating dynamic recovery by increasing the matrix deformation and promoting dynamic recrystallization through particle-stimulated nucleation. The unique fine-grained microstructure, uniformly dispersed NiTip, and well-bonded NiTip/Al interface significantly enhance strength without adversely affecting ductility.

II. Fabrication Technologies for Aluminum Matrix Composites - Additive Manufacturing (Arc Additive)

Arc additive manufacturing is a directed energy deposition (DED) 3D printing technology based on arc welding principles, constructing parts by depositing metal materials layer by layer.

The grain size of the TiN/Al-Zn-Mg-Cu alloy is refined from 459.3 μm to 104.6 μm, attributed to the formation of Al₃Ti particles acting as nucleating agents, resulting in increased tensile strength in both the horizontal and vertical directions. In the horizontal direction, the tensile strength increases from 207 MPa to 284 MPa.

Forming and Processing of Aluminum Matrix Composites

III. Forming and Processing of Aluminum Matrix Composites - Hot Extrusion

Hot extrusion enables the production of complex cross-sectional profiles, with only compressive and shear stresses applied during the forming process, resulting in good surface finish of the produced parts. Computer simulation can assist process engineers in understanding the metal flow patterns during profile extrusion, predicting defects in advance, optimizing die design, and improving profile quality.

III. Forming and Processing of Aluminum Matrix Composites - Forging

Based on the simulation of material flow behavior, potential deformation defects can be predicted, providing a theoretical basis for formulating process measures to prevent crack formation. By establishing a hot working map based on the dynamic material model, the optimal processing conditions for the material can be accurately predicted.

A multi-scale thermo-mechanical coupling model for composites was established to simulate the deformation process and microstructure. As a result, SiC/Al forgings with diameters ranging from 1760 to 2500mm were successfully developed in one attempt.

Numerical simulations of the isothermal forging process for blades/housings were conducted using finite element software to obtain strain distribution and load data. Reasonable forging process parameters were then formulated, ultimately resulting in forgings with ideal microstructure and properties.

By combining finite element simulation with hot compression experiments, the influence of deformation process parameters on the damage field, stress-strain field, and temperature field during the forging process of SiCp/Al composites was investigated.

The issue of cracking in heterogeneous and difficult-to-deform composite forging blanks was addressed through a combination of upset forging with a can and two-way forging processes. Large annular forgings of aluminum matrix composites were successfully trial-produced using isothermal precision die forging, with excellent forming quality and significantly refined shape and dimensions.

Forming and Processing of Aluminum Matrix Composites - Rolling

By simulating the residual stress distribution during the rolling process, rolling process parameters can be optimized to reduce residual stress generation, thereby improving the quality and precision of rolled products. During the rolling process, there exists a mechanism of small-sized phase fragmentation and phase transformation, as well as a refinement mechanism where large-sized phases are broken down into smaller ones.

After rolling, the material forms a fibrous microstructure with grains aligned along the rolling direction, resulting in an elongated grain structure. Rolling can be divided into cold rolling and hot rolling. Cold rolling significantly increases strength and hardness due to work hardening effects, but reduces plasticity. Hot rolling results in a more uniform microstructure with lower internal stresses, but lower strength.

By optimizing rolling parameters and process routes, profiles suitable for automotive or aerospace applications can be prepared.

III. Forming and Processing of Aluminum Matrix Composites - Welding

On an A356 aluminum alloy substrate, a gradient structure composite can be manufactured using a brazing layer of SiCp/Al composite with varying contents. The welding area is defect-free, continuous, and free of cracks and pores, with good bonding at the gradient structure interface.

III. Forming and Processing of Aluminum Matrix Composites - Machining

Particle-reinforced aluminum matrix composites: The main parameters affecting the grinding process include grinding wheel speed (vs), table speed (vw), grinding depth (ap), and maximum undeformed chip thickness (hmax). Among these, grinding at high grinding wheel speeds (vs) results in composites with higher surface quality and more ductile deposition zones.

Reducing the undeformed chip thickness (hmax) will decrease the number of effective abrasive grains involved in grinding, thereby controlling the pore size on the composite surface and the thickness of the damaged layer, which is beneficial for reducing the formation of subsurface microcracks and pores.

The main parameters affecting the turning process include spindle speed (n), feed rate (f), nose radius (r0), cutting depth, etc. Low spindle speed and feed rate are conducive to reducing stress concentration in composites, minimizing the collapse, pull-out, and pitting of SiCp.

Whisker-reinforced aluminum matrix composites: The reinforcement phase consists of whiskers with a large aspect ratio, exhibiting anisotropy, making the cutting process more complex.

Applications of Aluminum Matrix Composites

IV. Applications of Aluminum Matrix Composites - Overseas

It introduces the overseas applications of aluminum matrix composites and points out that the development of overseas discontinuous aluminum matrix composites is driven by demand and technological innovation, closely integrating the optimization of preparation processes with multi-domain requirements.

Aerospace: The development of lightweight, high-strength, and high-modulus aluminum matrix composites has made it possible to manufacture lightweight, flexible, and high-performance aircraft and satellites in the modern aerospace industry.

Weaponry: Discontinuous reinforced aluminum matrix composites possess characteristics such as lightweight, high strength, high-temperature resistance, and impact resistance in the weaponry field, significantly enhancing equipment mobility, battlefield survivability, and service life.

3C Electronics: Aluminum matrix composites, particularly SiC-reinforced aluminum matrix composites, are suitable for manufacturing electronic device liners, heat sinks, and other electronic components due to their advantages of low thermal expansion coefficient, low density, and good thermal conductivity.

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