Study On Fabrication And Properties Of High Entropy Alloy Reinforced Aluminum Matrix Composites

As an important material of automobile engine,piston has become a high-tech product with light weight and high performance.ZL109 aluminum alloy is one of the common piston materials,its comprehensive performance does not meet the current technical requirements.As a new type of alloy with excellent comprehensive properties,high entropy alloy has natural interfacial wettability and good interfacial compatibility with aluminum alloy matrix,and has become one of the first materials for reinforcement of aluminum matrix composites.So,the high entropy alloy was selected as reinforcement to improve the comprehensive performance of ZL109.In this paper,AlFeCrCoCu high entropy alloy was prepared by mechanical alloying and AlFeCrCoCu/ZL109 composite was prepared by powder metallurgy.The effects of hot pressing temperature,sintering temperature of the composites and the content of reinforcement on the comprehensive properties of the composites were studied by testing the phase composition,microstructure,mechanical properties and thermal expansion properties of the composites with the scanning electron microscope,X-ray diffraction,microhardness tester and thermal expansion instrument.The main conclusions are as follows:(1)The theoretical calculation of the phase formation of the high entropy alloy and the analysis of the experimental results show that the AlFeCrCoCu high entropy alloy is composed of a large number of solid solutions with simple crystal structure of BCC and a small number of solid solutions with simple crystal structure of FCC.(2)Hot-pressing temperature and enhance the body content had a greater influence on the mechanical properties of composite materials,When sintering temperature at 550??590?,there is a little impact on the mechanical properties of composite materials.When the sintering temperature and the content of reinforcement remain the same,and the hot pressing temperature is 550?,the tensile strength of the composites increases from 168.7 MPa to 326.4 MPa,which is 93.5%higher than that of the composites without hot pressing.The hardness was also increased from 108 HV0.01 to157 HV0.01,increasing by 45.7%.When the sintering temperature and hot pressing temperature remain unchanged and the reinforcement mass fraction is 15%,the tensile strength of the composite reaches the maximum,which is 128.7%higher than that of the ZL109 matrix material.When the reinforcement mass fraction is 20%,the hardness of the composite reaches the maximum,which is increased by 179.9%compared with the matrix material.(3)The thermal expansion coefficient of the composite increases with the rising of hot-pressing temperature,and gradually declines with the increase of reinforcement mass fraction.High entropy alloys reinforcement can effectively reduce the thermal expansion coefficient of ZL109 alloy material.The sintering temperature,at 550??590?,has a little impact on the properties of the thermal expansion of composite materials.(4)The wear resistance of the composites increases first and then decreases with the increase of the content of reinforcement.In the same friction experiment,the wear amount of 15%AlFeCrCoCu/ZL109 composites is less than 1/6 of the matrix wear amount,and the high entropy alloy can effectively improve the wear resistance of the aluminum alloy.(5)The phase composition of AlFeCrCoCu/ZL109 composites will not be changed by hot pressing.The microstructure distribution uniformity of AlFeCrCoCu/ZL109composites can be effectively improved and some microstructure defects can be eliminated at appropriate hot pressing temperature.The phase composition of AlFeCrCoCu/ZL109 composites is basically unchanged at different sintering temperatures,but with the increase of sintering temperature,a small amount of new intermetallic phase Al₁₃Co₄ is formed.With the increase of the mass fraction of reinforcement,the distribution uniformity and directivity of reinforcement in the matrix gradually become worse,and too high content of reinforcement will lead to particle agglomeration,pores and other defects in the microstructure.