Study On Microstructure And Properties Of Microwave-assisted Sintered Ferromagnetic FeCoNi_1.5CrCu_p/Al Matrix Composites

High-entropy alloy particle reinforced aluminum matrix composite is a new type of composite material,which can reduce the material consumption and improve the mechanical properties of the material.In this paper,high-entropy alloy FeCoNi_1.5CrCu particles and Al powder prepared by mechanical ball milling were used as raw materials,and FeCoNi_1.5CrCu_p/Al composites were prepared by powder metallurgy and microwave bidirectional assisted sintering.The effects of particle size and morphology of metal powder on the densification of microwave sintering were investigated.By means of TEM,SEM,EDS,XRD diffraction analysis,nano-indentation,microhardness and compression properties,the effects of microwave sintering temperature and the addition amount of high-entropy alloy FeCoNi_1.5CrCu reinforcing particles on the microstructure,phase evolution and mechanical properties of the composites were characterized.The main conclusions are as follows:(1)After the optimization of milling parameters,the morphology of pure Al powder is flaky,and the powder activity increases with the increase of specific surface area.After ball milling,the particle thickness is less than 5?m,which is close to the microwave skin depth of metal,and the corresponding eddy heating fraction is 96.8%.The temperature rise rate of pure Al powder with smaller particle size is faster,and the sintering temperature can reach higher at the same time.The mechanical alloyed FeCoNi_1.5CrCu high-entropy alloy has FCC structure and particle size is less than 3?m.After ball milling,the powder is evenly distributed around the pure aluminum particles.When the addition amount of HEA particles increases from 20 wt.%to 60wt.%,the coerseity of powder compacts increases from about 23 Oe to nearly 98 Oe,and the hysteresis loss increases accordingly,which improves the total microwave loss of powder compacts,and is beneficial to the densification process of composite powder in microwave sintering.(2)The effects of different microwave sintering temperatures on the properties and microstructure of the composites with 14 wt.%HEA_paddition amount were studied.The results of SEM,XRD and TEM show that with the increase of microwave sintering temperature,the density of the composites increases,and the distribution of the reinforcing particles is more uniform.The microstructure of the composites is the best at 480?.However,when the temperature was up to 500?,particles began to gather,and when the temperature was 520?,EDS found that particles and matrix elements had serious mutual diffusion,the structural stability of the HEA changed from FCC structure to FCC+BCC structure,and hard brittle Al₅Cr₈and other intermetallic compounds appeared at the matrix and interface of the composite.The nano-indentation test showed that the bonding strength between the reinforced particles and the matrix was the best at 480?,and the interfacial microhardness and elastic modulus reached 1245.3 MPa and 66.45 GPa,respectively.At this time,the density and hardness of the composite reached 99.2%and 138.5 HV,both at a high level.At 480?,the compressive strength and yield strength of composites is 405.2 MPa and 276.7 MPa,and the maximum shrinkage rate is 65.5%,and the composites have good strength and toughness.(3)The effects of FeCoNi_1.5CrCu particle addition on the microstructure and mechanical properties of FeCoNi_1.5CrCu_p/Al composites at 480?were investigated.The results show that when the reinforcement content is 15 wt.%,the microstructure of the composites is the best,the pores at the interface are the least,and the distribution of reinforcement phases is relatively uniform.Moreover,only Al and FeCoNi_1.5CrCu crystal phases exist in the composites,which ensures the interface clean.The nano-hardness at the interface of the composite material is 1286.36 MPa,and the elastic modulus is 69.53 GPa,which can achieve a high interface bonding.In addition,when the reinforcement content is 15 wt.%,the hardness of the composite reaches 146.3 HV,and the density of the composite reaches 99.3%.When the reinforcement content is more than 20 wt.%,the density decreases gradually.When the reinforcement content is 15 wt.%,the yield strength and compressive strength of the composites are up to?287.6 MPa and?418.8 MPa,and the maximum expansion rate of the composites is up to 65.2%,and the composite strength and toughness reach a higher level.