Preparation And Properties Research Of Al-based Composite By Melting Technique

Al-based composite is one of the research hotspots in the field of materials, at present,the main preparation technologies include stir-casting, melt infiltration, powdermetallurgy, spray deposition, in-situ synthesis and so on. The ceramic particlereinforced Al-based composites which combine the advantages of reinforcements andmatrixes have high specific strength and modulus, good thermal conductivity, excellentwear resistance, stable dimension. In addition, the preparation process is simple and thecost is low, so these materials are widely applied in aerospace, automotive. The C/Al orC, Particle/Al composites which make full use of the high thermal conductivity ofcarbon materials are widely applied in electronic components as major cooling material.In this thesis, the two types of Al-based composites were prepared by meltingtechniques, then tested and characterized comprehensively. The materials with highperformance were expected to be obtained through craft innovations based onlegitimately raw-material selection. At first, SiCp/2024Al composites were fabricatedby stir-casting, the effect of particle modification, Ti modification, hot extrusion andsolution&aging, stirring process parameters and particle content on the mechanicalproperties of composites were mainly investigated. Then, SiCp/ADC12compositeswere fabricated by pressureless infiltration, SiC/Gr/ADC12and AlN/Gr/ADC12composites were fabricated by pressure infiltration. The effect of reinforcement contenton the thermal properties of composite was mainly investigated.The results are as follows: in the stir-casting experiment, SiC particle modificationcan significantly improve the wettability between the particles and the matrix. Themechanical properties of matrix and composites are enhanced by increasing Ti content.The SiCp/Al interface bonding is strengthened by hot extrusion, so the performance ofas-extruded materials is much higher than as-cast. The optimal stirring processparameters are760℃,30min,9.5Hz-10.5Hz respectively. The comprehensivemechanical properties of composites attain the best under the condition of3wt.%particle content. The as-extruded tensile strength and brinell hardness reaches311MPaand133HB respectively, which improves by94.4%and84.7%compared with as-cast2024alloy matrix. The friction and wear test shows that the average friction coefficientand wear amount of as-extruded composite is0.6,0.25mg respectively, whichdecreased by25%and39%compared with2024alloy matrix under the same processcondition. After the solution&aging treatment, both the tensile strength and brinell hardness increase by about10%compared to the as-extruded. In the pressurelessinfiltration experiment, both the thermal conductivity and expansion coefficientdecrease with increasing particle content. In the pressure infiltration experiment, thecomposites show anisotropy obviously, in detail, the thermal conductivity in the XYdirection increases gradually with decreasing volume ratio of SiCp/Gr, however, Zdirection is opposite; the thermal expansion coefficient in the XY direction decreasesslowly while the Z direction increases gradually. When the volume ratio of SiCp/Grreaches3:7, the composite has the best thermal properties in the XY direction. Thethermal conductivity is206.4W/(mK),1.7times compared with the ADC12matrix; thethermal expansion coefficient is10.2×10-6/K,42.4%lower than the ADC12matrix. AlNparticles own higher thermal conductivity than SiC particles, when they were addedinstead of SiC, the thermal conductivity under the same condition reaches233.9W/(mK),1.9times compared with the ADC12matrix, further increased13.3%compared with the SiC/Gr/ADC12composite.