Investigation On Microstructure And Properties Of Nano-diamond Particles Reinforced Aluminum Matrix Composite

Aiming at the problems of traditional SiC particles reinforced aluminum matrix composites used in inertial devices,5 wt.%nanodiamond reinforced 2024Al matrix composites（ND/2024Al）were fabricated using nano-diamond（ND）as the reinforcement in this study.The influence of the ball milling process on the microstructure,mechanical properties,thermal conductivity and thermal expansion properties of nano-diamond/2024Al composites were studied.The following research results have been achieved:1.The sintering process affects the microstructure and properties of nano-diamond/2024Al composites.Increasing sintering temperature decreases the deformation ability of 2024Al alloy particles in the hot pressing sintering process,which enhances the plastic fluidity of 2024Al alloy particles and,filling ability to the pores between the particles.Consequently,the porosity of the nano-diamond/2024Al composites decreases and the hardness increases.The nano-diamond/2024Al composites sintered for 2 h at sinter temperature of 500 ^oC and sinter pressure of 60MPa have the highest density and hardness.2.The ball milling process has a significant effect on the microstructure of nano-diamond/2024Al composites.Both increasing ball milling speed and prolonging the ball milling time are beneficial to refine the size of nano-diamond/2024Al particles and improve the distribution of nano-diamond in 2024Al powder,resulting in the improvement of microstructure of sintered nano-diamond/2024Al composite.However,too long milling time or too high milling speed cause the reaggregation of nano-diamond,which reduces the distribution uniformity of nano-diamond inα-Al matrix.The nano-diamond/2024Al composite prepared by ball milling at 300 rpm for 5 h had the best microstructure,in which the distribution of nano diamond inα-Al matrix is the most uniform.3.Nano-diamond significantly increases the hardness and compressive strength of 2024Al.Moderate high-energy ball milling refines the grains of nano-diamond/2024Al composites,decreases the aggregation of nano-diamond reinforcements.It enhances the fine-grain strengthening effect of 2024Al matrix and the dispersion strengthening effect of nano-diamond and thus further increases the hardness and compressive yield strength of the composite.The nano-diamond/2024Al composite prepared by 250rpm-300rpm ball milling for 5 hours maximum compressive yield strength of 300～334MPa,which increases by 85%～108%compared with2024Al alloy（161.2MP）.4.The addition of nano-diamond reduces the thermal conductivity of 2024Al alloy.,Ball milling further decreases the thermal conductivity.The reason is that there exist a large number of nano-diamond/α-Al interfaces in the composites due to the extremely fine particle size of nano-diamond,which reduced the heat conduction.High energy ball milling make the nano-diamond dispersed more evenly in theα-Al matrix and produces more nano-diamond/α-Al interfaces.Hence,the thermal conductivity further decreases with the increase of ball milling energy.5.Addition of nano-diamond and ball milling treatment decreases the thermal expansion coefficient of 2024Al alloy.The nano-diamond/2024Al composites prepared by ball milling at 300 rpm for 9 h has the lowest thermal conductivity and thermal expansion coefficient.The thermal expansion coefficient of 2024Al alloy decreased from 23.7×10^-6/K to 12.3×10^-6/K,a decrease of 48.1%.The reason is that the dispersion strengthening effect of nano-diamond reinforcement improves the plastic deformation resistance ofα-Al matrix.The thermal mismatch stress on the nano-diamond/α-Al interface can only be released through the elastic deformation or slight plastic deformation ofα-Al matrix at the interface,which significantly reduced the thermal expansion coefficient of 2024Al.6.To meet the requirement to the matching between mechanical properties and CTE of dimensional stability of nano-diamond/2024Al composites,the ball milling process of 250-300 rpm ball milling speeds and 5-7 hours ball milling times are worth recommending,which causes an increase by 95-108%in compressive yield strength and a decrease by 30-35%in CTE compared with 2024Al alloy respectively.