Study On The Process,Microstructure And Properties Of FeCoNiTi_0.4Cr_0.5Al_0.6 High Entropy Alloy Particles Reinforced 6061 Aluminum Matrix Composites

Aluminum matrix composites?AMCs?have gained considerable attention as potential lightweight materials for structural applications due to their low density,high stiffness and high elastic modulus.Ceramic particles?Al₂O₃,Ti B₂,B₄C and Si C,etc.?,which possess high stiffness,strength and hardness,are usually used as the reinforcements in AMCs.However,owing to poor wettability between the ceramic particles and the matrix,a relatively weak bonding interface is generally formed,giving rise to the nucleation of the crack under loading.Moreover,it is always a problem that the difficult processing characteristics of ceramic particles reinforced aluminum matrix composites.Recently,multi-principal-component high entropy alloys?HEA?attracted our attention.Because of their outstanding performances,such as high strength,high hardness,exceptional thermal stability and good wear resistance.Additionally,the study found that the HEA particles reinforced metal matrix composites can generate good interface bonding,which is essential to mechanical properties of composites.In this work,Co Ni Fe Al_0.4Ti_0.6Cr_0.5 particles were prepared by mechanical alloying,and aluminum matrix composites were successfully prepared by the ball milling-hot pressing-hot extrusion process.Effects of the different volume fractions of HEA particles and ball milling times as well as hot pressing temperature on the microstructure and mechanical properties of aluminum matrix composites were investigated.The main results are as follows:?1?Nanocrystalline Co Ni Fe Al_0.4Ti_0.6Cr_0.5 particles were successfully prepared by mechanical alloying,with an average particle size of?12?m.Co Ni Fe Al_0.4Ti_0.6Cr_0.5 high-entropy alloy particle reinforced 6061 aluminum matrix composites were prepared by ball milling-hot pressing-hot extrusion process.The study found that the hot extrusion process can significantly improve the structure distribution of the composite material,significantly reducing the aggregation of large HEA particles in the hot-pressed sample,and the HEA particles are distributed in a band along the extrusion axis.There is no obvious interface reaction between the reinforcement and the matrix in the as-extruded composites.?2?The addition of HEA particles can significantly improve the strength of the composites in comparison to that of unreinforced 6061Al.As the volume fraction of the HEA particles increases,the tensile yield strength of the composite increases first and then decreases When the volume fraction of HEA particles is 10%,the HEA particle distribution of the composite is the most uniform,which can effectively block the movement of dislocations.Its tensile yield strength reaches 179 MPa,which is 27%higher than that of 6061 aluminum matrix?141 MPa?,and fracture strain is 12.3%.When the volume fraction of HEA particles is 15%and 20%,there are obvious HEA particles agglomeration and pores in the composite,which greatly reduces the mechanical properties of the composite.?3?The milling time has important effects on the distribution of the HEA particles,grain structure and mechanical properties of composites.With the increase of the ball milling time,HEA particles are gradually broken,and small HEA particles increase.And the banding phenomenon and particle clusters become more obvious.When the milling time is 10 h,the best distribution of HEA particles can be achieved.The ultimate strength and fracture strain of the 6061Al-HEA-10h composite are 378 MPa and 8.4%.Increase milling time to 20 h,the mechanical properties show the decreased tendency,as a result of the inhomogeneous HEA particle distribution and the introduction of oxide after a long milling time.However,when the milling time is up to 40 h,the composite presents the highest strength?385 MPa?,and the strain is close to that of the 6061Al-7.5HEA-20h composite,mainly resulting from the formation of obviously heterogeneous grain structure.The increased yield strength is minly ascribed to grain refinement,load transfer effect as well as geometrically necessary dislocations strengthening.Among them,grain refinement makes the most contribution to the yield strength.?4?As the hot pressing temperature increases,the fluidity of the composite powder increases,and the holes gradually decrease.The interface layer gradually thickens.At 510?,the composites has a good interface reaction,resulting in an appropriate interface layer,0.4?m.The tensile yield strength and fracture strain reach 198 MPa,9.5%.