Fabrication And Dynamic/Quasi-static Properties Of Lightweight High Entropy Alloy Reinforced Aluminum Matrix Composites

Particle reinforced aluminum matrix composites possess the advantages of high specific strength,high specific stiffness,good corrosion resistance and simple preparation process,so they are widely used in aerospace,electronic packaging and rail transportation.High entropy alloys not only have the advantages of high strength,high hardness and good thermal stability,but also have good wettability with aluminum alloy matrix.As reinforcements,the comprehensive mechanical properties of aluminum matrix composites can be significantly improved.Therefore,in recent years,high entropy alloy particles reinforced aluminum matrix composites have attracted more and more attention of researchers.In this paper,Al_50-xTi_xCr₂₀Mn₂₀Cu₁₀(x=10,15)lightweight high entropy alloy powders and bulks were prepared by mechanical alloying and Spark Plasma Sintering.The microstructure and mechanical properties of the two lightweight high entropy alloys were analyzed.Subsequently,(Al₃₅Ti₁₅Cr₂₀Mn₂₀Cu₁₀)p/6061Al composite was prepared by Spark Plasma Sintering using the optimized Al₃₅Ti₁₅Cr₂₀Mn₂₀Cu₁₀ high entropy alloy as the reinforcement and 6061Al as the matrix.The effects of sintering temperature on the mechanical properties and microstructure of composites were investigated.The effects of volume fraction and strain rate on quasi-static and dynamic compressive mechanical properties of composites were studied.The conclusions are as follows:(1)The Al_50-xTi_xCr₂₀Mn₂₀Cu₁₀(x=10,15)high entropy alloy powders prepared by mechanical alloying method are both single-phase supersaturated BCC structure.the average particle size of Al₃₅Ti₁₅Cr₂₀Mn₂₀Cu₁₀ high entropy alloy powder is 12.04?m,and the grain size is 22 nm.After sintering,the Al₃₅Ti₁₅Cr₂₀Mn₂₀Cu₁₀ high entropy alloy bulk changed from single-phase supersaturated BCC structure to BCC+FCC+Ti(Cu,Al)₂ three-phase structure.The density of the high entropy alloy is 5.31 g/cm³.yield strength,compressive strength and Vickers microhardness were 1892 MPa,2118 MPa and 875 HV,respectively;The specific strength of the high entropy alloy reaches 399 MPa·cm³·g^-1.(2)The sintering temperature produced a significant effect on the interface bonding between the matrix and the reinforcement of 5 vol.%Al₃₅Ti₁₅Cr₂₀Mn₂₀Cu₁₀/6061Al composite.When the sintering temperature is 520?,there was no diffusion layer between the matrix and the reinforcement.When the sintering temperature increases to 540?,a diffusion layer with a thickness of about 0.6?m appears between the matrix and the reinforcement,and the interfacial bonding is dominated by diffusion bonding.When the sintering temperature further increases to560?,due to the emergence of local liquid phase,obvious pores appear near the diffusion layer.When the sintering temperature is 540?,the composite has the best interface bonding state and comprehensive mechanical properties,and the Brinell hardness,tensile strength and yield strength of the composite are 93.2 HB,280 MPa and 194 MPa,respectively.The analysis shows that the diffusion layer can transfer the external load from the matrix to the reinforcement,which plays a bridge role.At the same time,the introduction of Al₃₅Ti₁₅Cr₂₀Mn₂₀Cu₁₀ high entropy alloy reinforcement will cause dislocation density increase and grain refinement,and the strength of the composite is significantly improved under the synergistic effect of these effects.(3)When the sintering temperature is 540?,the quasi-static compressive yield strength of(Al₃₅Ti₁₅Cr₂₀Mn₂₀Cu₁₀)p/6061Al composites with volume fraction of 5%,10%and 15%is 194MPa,289 MPa and 435 MPa,respectively,which is close to the calculated value of Iso-strain model of mixed law.When the volume fraction is 5%and 10%,the composites also show good plasticity,and the compression ratio are 33%and 25%,respectively.As the volume fraction increases to 15%,the plasticity of the composites decreases sharply due to the agglomeration of the reinforcement,and the compression ratio is 8%.(4)The yield strength of(Al₃₅Ti₁₅Cr₂₀Mn₂₀Cu₁₀)p/6061Al composites with volume fraction of 5%and 10%is improved in varying degrees compared with quasi-static compression during dynamic compression.The introduction of reinforcement significantly increased the strain rate sensitivity of the composite,and the strain rate sensitivity factor of the10 vol.%Al₃₅Ti₁₅Cr₂₀Mn₂₀Cu₁₀/6061Al composite reached 0.2,which was about four times that of the 6061Al matrix.The analysis shows that when the strain rate is lower than 2700 s^-1,the strain rate hardening effect plays a leading role,and the flow stress of the two composites increases with the increase of strain rate.When the strain rate exceeds 3000 s^-1,the adiabatic softening effect is more obvious,and the flow stress of the two composites decreases to a certain extent.The failure analysis of composite under dynamic compression shows that when the strain rate is less than 2000 s^-1,the composite specimen is continuously upset during dynamic compression,but there is no crack on the surface.With the further increase of strain rate,10 vol.%Al₃₅Ti₁₅Cr₂₀Mn₂₀Cu₁₀/6061Al composites appear cracks from the edge to the center,and a large number of Al₃₅Ti₁₅Cr₂₀Mn₂₀Cu₁₀ high entropy alloy reinforcements and diffusion layers rupture near the cracks.When the strain rate exceeds 3000 s^-1,fracture occurs at the edge of the composite sample.