| Carbon fiber-reinforced aluminum matrix(Cf/Al)composites have been considered as the advanced lightweight structural materials for space camera due to the low density,high strength and modulus,machinability,high temperature resistance and good machinability.However,one of the major issues is the poor wettability between carbon fiber and aluminum matrix during the fabrication of composites.The poor wettability leads to the difficulty for the infiltration of aluminum melt into the intra-bundle area of carbon fiber.In addition,the unavoidable interface reaction between carbon fiber and aluminum melt may happen in a high preparation temperature environment.The interfacial reaction not only damages the structure of carbon fiber,but also seriously affects the comprehensive properties of the composites.In order to improve the wetting behavior and prevent the chemical reaction between carbon fibers and the aluminum matrix and prepare Cf/Al composites with excellent mechanical properties,some effective methods have been put forward in the present paper.Firstly,conventional electroplating equipment was improved and a new electroplating technique assisted with the ultra-sonic vibration was used to deposit metallic coatings(Ni coating and Cu coating)on the carbon fibers.Then,metal-coated carbon fibers were used to fabricate the composites by the squeeze melt infiltration technique under vacuum condition.The effects of coating types(Ni and Cu coating),the infiltration temperature,coating thickness and the volume fraction of fibers on microstructure and mechanical properties of composites were investigated to realize interface control and optimization of mechanical properties of Cf/Al composites.On this basis,in order to further improve the damping capacities and isotropy of Cf/Al composites,a colloidal dispersion and suction filtration method was developed to fabricate aluminum matrix composites reinforced by SiC particles and short carbon fibers(SiCp/Csf/Al composites).The effects of carbon fibers and SiC particles hybrid reinforcements on the mechanical properties of aluminum matrix composites were analyzed.The main conclusions are listed as follows:(1)The inhomogeneous deposition of coating in the center area of the carbon fiber bundle was effectively avoided by the assistance of the ultrasonic vibration and the pre-oxidation treatment of carbon fibers.The additives in electroplating solution can refine the coating grain and improve the bonding strength between coating and carbon fiber.The effects of electroplating parameters on the quality of coatings were investigated.It was found that when the pH value of the electroplating solution was between 3 and 4,the current density was greater than 0.3 A/dm2,the electroplating time was between 4 min and 12 min and the temperature of plating solution was controlled between 20℃ and 40℃,a homogeneous nickel coating could be deposited on carbon fibers.When the pH value of the electroplating solution was between 0.8 and 1,the current density was between 0.7 A/dm2 and 1.1 A/dm2 and the electroplating time was between 4 min and 16 min,a homogeneous copper coating could be deposited on carbon fibers.(2)The microstructure and mechanical properties of Cu-coated carbon fiber-reinforced aluminum matrix composites and Ni-coated carbon fiber-reinforced aluminum matrix composites were compared and discussed.The results showed that compared with the uncoated fiber reinforced aluminum matrix composite,both Ni and Cu coatings can significantly improve the wettability and inhibit the interface reaction between carbon fibers and aluminum matrix during the process.However,the analysis of mechanical properties revealed the tensile strength of Cu-coated carbon fiber-reinforced aluminum matrix composites is better than that of Nicoated carbon fiber-reinforced aluminum matrix composites.The excellent mechanical properties for Cu-coated carbon fiber reinforced composites were attributed to the better compactness of the matrix and the modest fiber matrix interface bonding,which favor the load transfer ability from matrix to fiber under the loading state.(3)The effects of preparation conditions on the microstructure and mechanical properties of Cu-coated carbon fiber-reinforced aluminum matrix composites were studied.It was found that when the infiltration temperature was over 670℃,the molten aluminum could be fully immersed into the fiber bundle.When the coating thickness was 1.5 μm,the interfacial bonding strength between carbon fiber and aluminum matrix was moderate.When the infiltration temperature was 680℃,the coating thickness was 1.5 μm and the volume of fibers was 16%,the mechanical properties of the Cu-coated carbon fiber-reinforced aluminum matrix composites was excellent.Its tensile strength and elastic modulus were 233 MPa and 93 GPa respectively.Compared with the pure aluminum matrix(tensile strength and elastic modulus were 55 MPa and 70 GPa respectively),the tensile strength and elastic modulus of the Cucoated carbon fiber-reinforced aluminum matrix composites were significantly improved.However,compared with pure aluminum matrix,its damping capacitie is relatively low between 25℃ and 200℃ on the test condition of 5 Hz.(4)Aluminum matrix composites reinforced by SiC particles and short carbon fibers(SiCp/Csf/Al composites)were fabricated successfully by a colloidal dispersion and suction filtration process.The effects of volume fraction of reinforcement on the properties of SiCp/Csf/Al composites were studied.It was found that when the volume fraction of micronSiC particles was 5%and the volume fraction of fiber is 7%,the tensile mechanical properties and damping capacities of SiCp/Csf/Al composites were better.For tensile mechanical properties,its tensile strength and elastic modulus are 207 MPa and 92 GPa respectively.Compared with SiCp/Al composites with SiCp volume fraction of 5%,its tensile strength and elastic modulus are improved by 85%and 15%respectively.For damping capacities,compared with Cf/Al composites with Cf volume fraction of 16%,its damping capacitie is high between 25℃ and 300℃ on the test condition of 5 Hz.The synergistic strengthening effect is attributed to uniform distribution of SiCp and Csf in A1 matrix and the good interface bonding with Al matrix,which can not only improve the tensile mechanical properties of the composite,but also favor its damping capacities.(5)The properties of nano-SiCp/Csf/Al composites were compared with micron-SiCp/Csf/Al composites.The synergistic strengthening effect of nano-SiCp and fibers are more beneficial to improve the mechanical properties of aluminum matrix composites.Nano-SiCp have small size which could produce an Orowan strengthening effect in aluminum matrix composites.Meanwhile,nano-SiCp can be nailed at the interface between carbon fiber and aluminum matrix,which could improve the interface bonding strength between carbon fibers and aluminum matrix,and contribute to the strengthening effect of carbon fibers.In addition,the interface bonding between nano-SiCp and aluminum matrix was relatively weak and nano-SiCp may also refine the grain size of aluminum matrix,which could consume energy and improve the damping capacities of composites. |
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