High Entropy Alloy Reinforced Aluminum Matrix Composites Produced By Friction Stir Processing

Particle reinforced aluminum matrix composites(PRAMCs)have a bright application prospect in the aerospace,automotive industry and other fields because of their light weight,high specific strength,and good wear resistance.The interface bonding mechanism between reinforcement phase and matrix and its influence on the properties of composites have received extensive attention from researchers.However,the particle-reinforced aluminum-based composite materials that traditionally use ceramic particles as the reinforcement phase has poor interface bonding,which seriously affects the plasticity and toughness of the composite material.Due to the better interfacial wettability and compatibility between metals and metals,hard metal particles are used as the reinforcement phase,which is helpful for the composites to obtain good matching of strength and plasticity.The high entropy alloys (HEAs)have been considered promising candidates for reinforcement phase in recent years due to their high strength,high hardness,wear resistance and thermal stability which attributes to unique solid solution structure.Therefore,the AlCoCrFeNi_2.1 high entropy alloy was selected as the reinforcement phase,and the heat-treatable 6061-T6 aluminum alloy was used as the matrix in this study.In order to reduce the interface reaction,friction stir processing(FSP)as a solid-state processing technique was used to fabricate aluminum matrix composites,and then the composite materials were strengthened by T6 heat treatment.The phase composition,distribution of reinforcement phase,interface bonding and element diffusion in the composites were studied.The effect of the reinforcement phase content and heat treatment on the mechanical properties and tribological performance of the composite materials was analyzed,and the fracture mode and wear mechanism of the composite materials were discussed.The main conclusions obtained are as follows.The results showed that PRAMCs with good surface formation,no internal defects and uniform particle distribution could be obtained under repeated six-pass FSP at a rotation rate of 1200 rpm and a traveling speed of 80 mm/min.In the research of microstructure,it was found that the grain size of the composites was significantly refined due to the friction stir processing and the hindrance of reinforcement.There were three kinds of bonding interfaces in the composites,and the bonding interface was smooth and without defects.It also found that Si element from the matrix was enriched at the interface.When the content of reinforcement phase is 15 Vol%,the grain size of the composite was 3.63?m,which was much smaller than that of the Base(rolling direction?200?m).The degree of elements diffusion between the reinforcing phase and the matrix was different.So,there were three kinds of interface bonding formed in composites.After the heat treatment,it was found that the smaller reinforcing phase particles were partially decomposed.The mechanical properties of composites were studied.The increasing the content of reinforcement phase and aging treatment could improve the hardness and tensile strength of the composites.When the reinforcement phase content was 15Vol%,the hardness and tensile strength of the composites were 72 HV and 222.9 MPa,respectively.Compared with the FSPed-6061 without particles,the hardness and tensile strength of the composites were increased by 28.6%and 25.4%,respectively.After T6 heat treatment,the hardness of 15%-AMC_S-T6 reached 125 HV and the tensile strength was 332.1 MPa.The tribological performance of composites was researched.It was found that the wear resistance of FSPed-6061 was lower than that of the matrix after friction stir processing.The addition of reinforcement phase and T6 heat treatment were helpful to improve the tribological performance of the material.After heat treatment,the wear loss of 15%-AMC_Scomposites was 8.3 mg,which is 37.7%lower than that of matrix.The Base,FSPed-6061 and15%-AMCs occurred plastic deformation during friction and wear.The wear mechanisms were delamination and abrasive wear,severe delamination wear,adhesive and abrasive wear,respectively.The wear mechanism of 15%-AMCs-T6 was dominant by abrasive wear,because its less plastic deformation.