Aluminum and aluminum alloys have excellent properties such as low density, high strength, and good ductility, and are widely used in the aerospace and automotive industries. However, it is difficult to further improve the mechanical properties of aluminum and aluminum alloys using traditional methods such as component addition, heat treatment, and plastic deformation. The emergence of graphene and the development of graphene/aluminum composite materials using the addition of graphene have made it possible to improve the mechanical properties of aluminum alloys. Due to the thermodynamic instability of two-dimensional crystals, graphene, whether in a free state or deposited on a substrate, is not completely flat and has intrinsic microscale folds on its surface. This three-dimensional change can cause static electricity, leading to easy agglomeration of single-layer graphene and making it difficult to uniformly disperse in the composite matrix. At present, there are many studies on graphene reinforced polymer based and ceramic based composite materials, and some achievements have been made. In metal matrix composites (MMCs), due to the poor wettability between graphene and the metal matrix, graphene is difficult to disperse uniformly in the matrix, making research on graphene reinforced metal matrix composites challenging.
Aluminum and aluminum alloys have excellent properties such as low density, high strength, and good ductility, and are widely used in the aerospace and automotive industries. However, it is difficult to further improve the mechanical properties of aluminum and aluminum alloys using traditional methods such as component addition, heat treatment, and plastic deformation. The emergence of graphene and the development of graphene/aluminum composite materials using the addition of graphene have made it possible to improve the mechanical properties of aluminum alloys. Similarly, graphene/aluminum composites also face the problem of difficult dispersion of graphene, and in recent years, many researchers have conducted extensive research to address this issue.
This article provides an overview of the research progress in the preparation techniques of liquid and solid graphene/aluminum composites, with a focus on the dispersion methods of graphene in solid-state methods and the forming processes of composite materials.
1、 Preparation of Graphene Reinforced Aluminum Matrix Composite Materials by Liquid state Method
1. The conductive mechanism of graphene conductive ink:
The preparation of graphene/aluminum composite materials by liquid state method refers to adding graphene to a molten aluminum matrix and using traditional casting equipment to cool and solidify to obtain composite materials. This method has simple equipment, high production efficiency, low cost, no restrictions on shape and size, and can achieve large-scale production. These advantages make it have broad prospects for application and development.
However, the graphene/aluminum composite material prepared by this method has many pores, and due to the poor wettability and significant difference in specific gravity between graphene and aluminum, it is difficult to uniformly disperse graphene into the aluminum liquid; Furthermore, C and Al are thermodynamically unstable, especially when aluminum is in a molten state, they form needle shaped Al4C3 phase, which is a brittle phase sensitive to moisture and prone to pulverization in atmospheric environments, leading to poor performance of composite materials
Reduce. In order to prevent the reaction between graphene and liquid aluminum matrix and improve the wettability between graphene and liquid aluminum, it is often necessary to treat graphene to some extent.
The processing method is similar to that for carbon nanotubes and carbon nanofibers in metal matrix composites reinforced with carbon nanotubes and carbon nanofibers, usually using chemical plating (Cu, Au, etc.), physical vapor deposition, and chemical vapor deposition methods. Through continuous improvement of traditional liquid methods, researchers have proposed various liquid preparation methods, mainly including stirring melting casting, stirring friction method, in-situ reaction synthesis method, electrodeposition method, etc.
1.1 Mixing and melting casting method
The stirring melting casting method is a liquid preparation method that introduces reinforcement and evenly distributes it by mechanically stirring the melted metal under gas protection to generate eddy currents. Although the stirring casting method can relatively evenly distribute graphene into the aluminum matrix, there is still a problem of poor wettability between the matrix and the reinforcement.
In response to this, Guan Renguo et al. from Northeastern University conducted copper adsorption treatment on self-made graphene by stirring and mixing oxidized graphene with CuSO4 solution, heating it in a water bath to 98 ℃, and then adding excess hydrazine hydrate for 2 hours. After washing, filtering, and drying, graphene Cu was obtained. Through this treatment, the wettability between graphene and aluminum substrate was improved. Compared with chemical copper or nickel plating methods, this method has relatively lower preparation costs and environmental pollution levels. After copper treatment, the industrial pure aluminum ingot was prepared by mechanical stirring melting method. The ingot was heated and melted to 720 ℃ using an induction furnace and mechanically stirred. Meanwhile, self-made graphene Cu was continuously added. When the temperature of the aluminum liquid dropped to 660 ℃, the stirring resistance increased significantly. The stirrer was removed and the melt was air-cooled to room temperature to prepare graphene aluminum based composite materials. The hardness of the prepared composite material increased by 40% compared to pure aluminum ingots, but this method did not completely disperse graphene, and graphene still underwent severe agglomeration.
1.2 Friction Stir Method
Preparation of graphene reinforced aluminum based composite materials by friction stir method, derived from friction stir welding. The material in the processing zone is softened by the strong heat generated by the friction between the rotating shoulder and the workpiece, and the reinforcing body is uniformly mixed with the substrate by friction stir. The process schematic diagram is shown.
Graphene/aluminum composite materials were prepared using this method, where GO/water colloid was directly introduced onto the surface of the aluminum plate. During the stirring friction process, GO was reduced to graphene, while water was evaporated by frictional heat. By comparing the friction stir treatment of aluminum plate and GO aluminum plate, it was found that the friction stir process and the addition of graphene improved the ductility of the material, while the tensile strength of the material slightly decreased. The thermal conductivity of the graphene/aluminum composite material prepared was 15% higher than that of aluminum, which can be used to prepare inexpensive, lightweight, and high thermal conductivity heat converters. However, this method cannot accurately control the content of graphene during the preparation of composite materials, making it difficult to stably control the properties of the composite materials.
1.3 Electrodeposition method
Electrodeposition is the process of depositing metal or alloy from its compound aqueous solution, non-aqueous solution, or molten salt on the electrode surface under the action of an electric field. Li et al. from Zhengzhou University used electrodeposition to prepare graphene nanoparticles (GNPs)/aluminum composite coatings. Dissolve AlCl3 and LiAlH4 in an organic solvent mixture of anhydrous tetrahydrofuran and benzene with a volume ratio of 6:4, and add an appropriate amount of sonicated GNPs to a concentration of 5 g · L-1 to form an electrolyte. Using aluminum plates polished with sandpaper and treated with acid and alkali as positive and negative electrodes, insert the electrolyte in a parallel manner along the direction perpendicular to the horizontal plane of the electrolyte. The aluminum graphene coating was prepared by electromagnetic stirring of the electrolyte at a speed of 250 r/min at room temperature and electro deposition treatment at a current density of 5 A · dm-2 for 60 minutes. Compared with pure aluminum, the hardness of aluminum graphene coating has increased by 3.8 times; Under dry friction conditions, the friction coefficient decreases from 0.566 to 0.0504.
1.4 In situ reaction synthesis method
The fundamental difference between in-situ reaction synthesis method and the above methods is that the reinforcement is not externally added, but generated in situ through chemical reactions during the preparation process. The basic principle is: in a certain liquid alloy, the high temperature of the alloy liquid is used to cause chemical reactions between the alloy elements or between the alloy elements and compounds, generating one or several reinforcing phases, and then obtaining a metal based composite material reinforced by in-situ reinforcing phases through casting, in order to improve the performance of a single metal alloy. The composite material prepared by this method has small reinforcement particle size, high thermodynamic stability, no surface pollution, good compatibility with the matrix, high interfacial bonding strength, and eliminates the reinforcement pretreatment process, simplifying the preparation process.
2、 Preparation of Graphene Reinforced Aluminum Matrix Composite Materials by Solid State Method
The most commonly used method for preparing graphene/aluminum composites by solid-state method is powder metallurgy, and the typical powder metallurgy process flow is shown in Figure 2. The powder metallurgy method uses mechanical powder mixing to prepare composite powders, and the reinforcing body can be uniformly mixed with the matrix powder, and the content of the reinforcing body can be adjusted arbitrarily and accurately controlled; Due to the preparation temperature being lower than the melting point of aluminum,
It can effectively prevent the formation of harmful Al4C3 phase during the reaction between aluminum and graphene, which can damage the properties of the material; This low-temperature synthesis process can effectively control the interface between graphene and aluminum matrix, and limit the grain size of aluminum matrix. Powder metallurgy mainly consists of two steps: powder mixing and forming process. In order to further improve the density and uniformity of materials, hot deformation processing such as extrusion, hot forging, hot rolling, etc. are often carried out.
2.1 Mixing method
The effective dispersion of graphene in aluminum matrix is the primary challenge to be solved in the preparation of graphene/aluminum composite materials. Simple mechanical mixing of graphene and aluminum powder cannot completely disperse them evenly. In order to reduce the phenomenon of graphene agglomeration, various mixing methods have been proposed in literature, including ultrasonic dispersion, wet mechanical stirring mixing, ball milling, planetary high-energy ball milling, surface modification, and electrostatic adsorption.
2.1.1 Wet mechanical stirring and mixing
The simplest method of powder mixing is to directly mix graphene with the matrix aluminum powder, but the van der Waals forces and electrostatic interactions between graphene layers make it difficult for graphene to disperse, resulting in poor powder mixing effect. In order to improve the dispersibility of graphene and disperse the aggregated graphene, some researchers have proposed a method of mechanically stirring and mixing graphene with aluminum powder in organic solvents.
The self-made graphene nanosheets (GNSs) can be added to a cellulose (EC)/isopropanol (IPA) solution to obtain a dispersion system that can serve as a storage body for GNSs; Then add aluminum powder to the EC/IPA solution to obtain Al/EC/IPA dispersion. Mix the storage body of GNSs with the Al/EC/IPA dispersion and stir magnetically for 48 hours. Filter and dry to obtain GNSs/Al composite powder.
In order to further improve the dispersion uniformity of graphene, it is first dispersed before mixing with aluminum powder. The solvents commonly used for dispersing graphene include ethanol, acetone, or isopropanol. Rashad et al. sonicated graphene nanosheets (GNPs) with ethanol or acetone for 1 hour, then added the resulting GNPs dispersion dropwise to an ethanol/acetone suspension of aluminum powder, mechanically stirred for 1 hour, filtered and dried to obtain Al/GNPs composite powder.
In addition, compared to hydrophobic graphene, amphiphilic graphene oxide (GO) is more easily dispersed in various solvents, so GO is sometimes used as a raw material for graphene reinforced metal based nanocomposites. The dispersion solvent for GO often uses deionized water or ethanol.
2.1.2 Surface modification and charge attraction method
In order to improve the dispersibility of graphene, it is sometimes necessary to perform surface modification treatment on graphene or aluminum powder. By adding surfactants, the dispersibility and solution stability of graphene and aluminum powder can be improved. Surfactants can be divided into two categories: ionic and non-ionic. Ionic surfactants include sodium dodecylbenzenesulfonate (SDBS, anionic), sodium dodecyl sulfate (SDS, anionic), and hexadecyltrimethylammonium bromide (CTMAB, cationic), while nonionic surfactants include polyethylene glycol octylphenyl ether (TritonX-100), all of which can effectively maintain the stability of graphene nanosheets.
|
