Preparation And Properties Of 5052 Aluminum Matrix Composites Reinforced By Al_0.6CoCrFeNi High Entropy Alloy Particles

At present,particle reinforced aluminum matrix composite is one of the most widely used and most important metal matrix composites.However,there is a great difference between the properties of traditional particle reinforcement and aluminum matrix,which makes the composites have some problems that are difficult to solve.As a kind of alloy with good mechanical properties and good wettability with aluminum matrix,high entropy alloy has been used as reinforcement material.In order to investigate the properties of high entropy alloy reinforced aluminum matrix composites,Al_0.6CoCrFeNi/Al composites were prepared by vacuum hot pressing sintering.The effects of different volume fraction and particle size of reinforcements on the microstructure and properties of the composites were investigated,and the composites at different sintering temperatures were studied.Based on the heat treatment scheme of the composites obtained by hot pressing sintering,the microstructure and properties of the composites with heat treatment time of 0h～48h were studied.The results are as follows:Four kinds of particle sizes（<25μm,25-38μm,38-45μm,75-105μm）and three volume fractions（7%,15%,20%）of composite powders were obtained by ball milling,and then aluminum matrix composites were obtained by vacuum hot pressing sintering.It is found that when the reinforcement content is 7%and the particle size is 25-38μm,the microstructure of the composite is the most uniform.There is a new phase in the composite during sintering,which is mainly due to the self-diffusion of high entropy alloy elements and the solid solution precipitation of matrix elements,and there is a positive correlation between the density of the composites and the microstructure of the composites.The existence of critical distribution concentration makes the hardness,yield strength and compressive strength of the composites show different trends under different volume fractions.With the increase of sintering temperature,there is an obvious transition layer in the composites,the elements of the transition layer are mainly elements in high entropy alloy,the thickness of the transition layer increases with the increase of temperature,and the maximum thickness of the transition layer is～6μm,which is related to the solution limit of the matrix.The density,strength and hardness of the composites increased in turn,while the plasticity decreased.The comprehensive mechanical properties of the composites prepared at 650℃were better,and the yield strength was 117.3MPa,the tensile strength was 226.6MPa.When the heat treatment temperature is higher than 500℃,the interface layer of the shell-core structure of the composite is formed,and the thickness and integrity of the interface layer increase with the increase of holding time.Element diffusion occurs in high entropy alloy particles during heat treatment,and no new phase is formed.Due to the different diffusion rates of different elements in Al matrix,the element distribution of high entropy alloy elements in the interface layer is different,and the contents of Fe and Ni elements are higher.The micro-properties of the composites were obtained by nano-indentation,the properties of the interface layer are independent of the heat treatment conditions,and the increase of interface continuity and thickness reduced the hardness and modulus of the matrix by 11.0%and 2.5%.After heat treatment,due to the precipitation of the second phase particles and the formation of the interface layer,the hardness and yield strength of the composites will be enhanced,and the plasticity of the composites will decrease.